SYNTHESIS POLYETHERSULFONE-BASED AMPHIPHILIC BLOCK COPOLYMERS & DEVELOPMENT OF SINGLE-ION CONDUCTORS FOR

LITHIUM ION BATTERIES

By

Hui Zhao

A DISSERTATION

Submitted to Michigan State University

in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Chemistry

2012

 

ABSTRACT

SYNTHESIS POLYETHERSULFONE-BASED AMPHIPHILIC BLOCK COPOLYMERS & DEVELOPMENT OF SINGLE-ION CONDUCTORS FOR

LITHIUM ION BATTERIES

By

Hui Zhao

Polyethersulfone (PES) membranes often foul easily because of their

hydrophobicity, and addition of amphiphilic PES block copolymers to

membrane formulations may help overcome this problem. This dissertation

explores the synthesis and aggregation properties of relevant amphiphilic ABA

block copolymers, where PES is the hydrophobic B block and poly(2-

hydroxyethyl methacrylate) or poly(2-hydroxypropyl methacrylate) are the

hydrophilic A blocks. 1H nuclear magnetic resonance (NMR) spectroscopy,

Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric

analysis (TGA) confirm the block copolymer synthesis, and 1H NMR spectra

and TGA also provide consistent data on copolymer compositions.

Aggregation behavior of the copolymers in solvent/non-solvent mixture is

studied using NMR and dynamic light scattering (DLS).

Lithium ion batteries are now ubiquitous, but concentration polarization is

still a problem in the currently used battery electrolytes, especially in

high-current applications. Immobilizing anions and having lithium cations

contribute to most of the ionic conductivity is a good solution to address this

problem. This work aims to create nanoparticle-containing electrolytes using

silica nanoparticles modified with polyanions that have Li+ as the counterion.

Anion mobility is restricted by the polyanion polymer backbones, which is

further immobilized by the nanoparticles. The polyelectrolyte-grafted

nanoparticles were synthesized by surface atom transfer radical

polymerization (ATRP) of monomers from initiator-grafted silica nanoparticles.

To prepare a lithium-ion conductor, the polyelectrolyte-grafted nanoparticles

were blended with polyethyleneglycol (PEG) oligomer. Because the anions are

immobile, lithium is the only ion that conducts current. AC impedance shows

that the best conductivity is from a Bis(trifluoromethanesulfonyl)imide (TFSI)

analogue monomer around 10-6

S/cm, which is in the same range as a

monolayer-grafted silica nanoparticle system using similar TFSI analogue

structure. A proposed model shows that the multilayer-grafted nanoparticles

only have outermost layer of lithium cations accessible to the solution,

because of the low solubility of polyelectrolytes in the PEG solvent.

Direct modification of PEG via alkyne-azide or thiol-ene click chemistry as

single lithium ion conductor. To make sure 1,2,3-triazole or sulfur structure

from click chemistry is not impeding lithium transport, we synthesize

1,2,3-triazole and sulfur containing PEGs via step growth polymerization.

Conductivity measurement of lithium perchlorate with triazole containing PEG

or sulfur containing PEG shows similar data as the pure PEG, which proves

that click chemistry could be applied in the development of single-ion

conductors for Lithium Ion Batteries.

Copyright by HUI ZHAO

2012

v 

ACKNOWLEDGEMENTS

Dr. Gregory Baker – for his patience, encouragement, advice and intellectual

generosity

Dr. Merlin Bruening – for much appreciated advice and discussions on my

research project

Dr. William Wulff, Dr. Milton Smith and Dr. Babak Borhan– for being my

committee member

Many people, past and present, in the lab, Qin Yuan, Sampa Saha, Tomas

Jurek, Georgina Comiskey, Wen Yuan, Quanxuan Zhang, Heyi Hu, Yiding Ma,

Zhe Jia, Greg Spahlinger, Salinda Wijeratne.

Many people, in the department, in particular, Daniel Holms, Kathryn Severin

for their help on the instruments.

Finally, I would like to thank my family for their love and support.

vi 

TABLE OF CONTENTS  

 

LIST OF TABLES ............................................................................................ viii

LIST OF FIGURES ............................................................................................ x

LIST OF SCHEMES ....................................................................................... xiv

Chapter 1 Introduction ....................................................................................... 1 Part I: Synthesis of Polyethersulfone (PES)-Based Amphiphilic Block Copolymers ..................................................................................................... 1 Part II: Synthesis of Comb-Polyethyleneoxide (PEO) via Click Chemistry- New polymers for Possible Lithium Ion Conductors ....................................... 3 References ..................................................................................................... 8

Chapter 2 Synthesis of Polyethersulfone (PES)-Based Amphiphilic Block Copolymers ...................................................................................................... 13

Introduction ................................................................................................... 10 Polysulfone Materials and Their Application as Water Treatment Membranes ............................................................................................... 10 Block Copolymers ..................................................................................... 13 Polysulfone-Based Amphiphilic Copolymers ............................................ 17 Self-assembly of Block Copolymers ......................................................... 22 Block Copolymers as Phase Inversion Membrane Materials ................... 24 Unique Aspects of Self-assembly of Polysulfone-Based Block Copolymers .................................................................................................................. 27

Results and Discussion ................................................................................ 29 Purification of Hydroxypropyl Methacrylate (HPMA) Isomers .................. 30 Synthesis of PES with Hydroxyl End Groups ........................................... 33 Synthesis of a PES Macroinitiator and Use of a Model Compound to Explore the ATRP Catalytic System ......................................................... 36 Polymerization from a PES Macroinitiator ................................................ 42 GPC Analysis of HEMAn-PESm-HEMAn and HPMAn-PESm-HPMAn Block Copolymers ..................................................................................... 47 Infrared Spectra of the Block Copolymers ............................................... 53 TGA of the Block Copolymers .................................................................. 57 Critical Water Content (CWC) Values of PES and PES-based Block Copolymers ............................................................................................... 63 Aggregation of Block Copolymers in Dilute Solutions-NMR and DLS Studies ...................................................................................................... 72

vii 

Conclusion .................................................................................................... 81 Experimental Section ................................................................................... 82 Appendix A ................................................................................................... 91 References ................................................................................................... 98

Chapter 3 Use of the Nanoparticles and Click Chemistry in the Development of Single-ion Conductors for Lithium Ion Batteries ............................................ 102

Introduction-Ion Conduction in Lithium Ion Batteries ................................. 102 Results and Discussion .............................................................................. 106

Single-ion Conductors Containing Nanoparticles with Immobilized Anions ................................................................................................................ 106 Single-ion Conductors Prepared Using Nanoparticles Modified by Grafting of Polyanions .......................................................................................... 109 Towards Click Chemistry for Synthesizing Single-ion Conductors with a High Density of Lithium Ion PEO ............................................................ 113

Conclusions ................................................................................................ 126 Experimental Section ................................................................................. 127 Appendix B ................................................................................................. 135 References ................................................................................................. 154

 

viii 

LIST OF TABLES  

 

Table 2.1. Different conditions for synthesis of PES and the molecular weights and PDI values of the resulting polymer. ......................................................... 33

Table 2.2. Block Copolymers with their Molecular Weights and PDI Values. ......

......................................................................................................................... 46

Table 2.3. PDIs of various copolymers as determined from GPC data or calculated using equation (2) ........................................................................................... 52

Table 2.4. PolyHEMA Content in Copolymer Samples as Calculated from NMR Spectra and TGA under nitrogen ..................................................................... 60

Table 2.5. PolyHPMA Content in Copolymer Samples as calculated from NMR spectra and TGA. ............................................................................................. 63

Table 2.6. Commercial Polyethersulfones and their Molecular Weights, PDI Values and Terminal Groups. ........................................................................... 64

Table 2.7. Solubility Parameters of Several Solvents and Polymers at 25 oC. ......................................................................................................................... 68

Table 2.8. Evolution of the proton NMR signals from HEMA22-PES34-HEMA22 with increasing of D2O content in the DMSO-d6 solvent. ............................................................................................................. 75

Table 2.9. DLS particle sizes and particle volume percentages for aggregates of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures contained 1 mg/mL HEMA22-PES34-HEMA22. .............................................. 77

Table 2.10. DLS particle sizes and particle volume percentages for aggregates of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures contained 10 mg/mL HEMA22-PES34-HEMA22 ............................................ 79

ix 

Table 2.11. DLS particle sizes and particle volume percentages for aggregates of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures contained 30 mg/mL HEMA22-PES34-HEMA22. ............................................ 80

Table 2.12. Polystyrene standards used to calibrate the results of GPC in DMF. ......................................................................................................................... 84

Table 3.1. Lithium transference numbers for several lithium salts in battery solvents. ......................................................................................................... 105

Table 3.2. Particle weight percentages and O/Li for electrolytes prepared from Si-C5NTfLi dispersed in PEGDME-500. ........................................................ 108

Table 3.3. Particle weight percentages and O/Li ratios for electrolytes prepared from Si-TfMALi dispersed in PEGDME-500. ................................................. 110

 

x 

LIST OF FIGURES  

 

Figure 2.1. Equilibrium morphologies in AB diblock copolymers.. ................... 24

Figure 2.2. Phase inversion membranes made from PSf (upper left: SEM top view, upper right: edge view, NMP solvent), and PES (bottom: SEM edge view DMAc solvent). ................................................................................................. 26

 

Figure 2.3. SEM images of membranes prepared by phase inversion of poly(styrene)-co-poly(4-vinylpyridine). Peinemann’s work. Edge view (left), top view (right). Scale bars correspond to 500 nm.. .............................................. 27

 

Figure 2.4. Proton NMR 500 MHz spectra of an HPMA isomer mixture (bottom) and purified 2-hydroxypropyl methacrylate (top) in deuterated chloroform.. ... 32

 

Figure 2.5. ProtonNMR 500 HMz spectra of bisphenol sulfone (bottom) and BisphenolS-I (top) in deuterated DMSO... ..................................................... 37

 

Figure 2.6. ATRP kinetic plot for polymerization of HEMA using BisphenolS-I as an initiator and CuBr/PMDETA as the catalyst in DMF, the initial monomer concentration was 2 M... .................................................................................. 38

 

Figure 2.7. ATRP kinetic plot for polymerization of HEMA using ethyl bromoisobutyrate as an initiator and CuCl/CuCl2/PMDETA as the catalyst in NMP, the initial monomer concentration was 2 M... ........................................ 40

 

Figure 2.8. ATRP kinetic plot for polymerization of HEMA using ethyl BisphenolS-I as the initiator and CuCl/CuCl2/PMDETA as the catalyst in NMP, the initial monomer concentration was 2 M... .................................................. 41

 

Figure 2.9. ATRP kinetic plot for polymerization of HEMA using a PES macroinitiator and CuCl/CuCl2/PMDETA as the catalyst in NMP, the initial monomer concentration was 1.3 M... .............................................................. 42

 

Figure 2.10. Proton NMR 500 MHz spectra of (a) NMP, (b) HEMA26-PES42- HEMA26 and (c) macroinitiator in DMSO-d6... ............................................... 44

 

Figure 2.11. Gel-permeation chromatograms of (a) PES51 and (b) the copolymer HEMA9-PES51-HEMA9... .............................................................. 47

xi 

 

Figure 2.12. Gel-permeation chromatograms of (a) PES42 (b) copolymer HEMA13-PES42-HEMA13 and (c) HEMA26-PES42-HEMA26... ................... 49

 

Figure 2.13. Gel-permeation chromatograms of (a) PES34 and (b) HEMA22- PES34-HEMA22... ........................................................................................... 50

 

Figure 2.14. An ABA block copolymer with monodisperse A block and polydisperse (PDI=2.0) B blocks... .................................................................. 51

Figure 2.15. Gel-permeation chromatograms of (a) PES42, (b) HPMA12- PES42-HPMA12 and (c) HPMA26-PES42-HPMA26... ................................... 53

Figure 2.16. IR spectra of (a) PES, (b) polyHEMA and (c) HEMA22-PES34- HEMA22... ........................................................................................................ 54

 

Figure 2.17. IR spectra of (a) HEMA9-PES51-HEMA9, (b) HEMA13-PES42- HEMA13, (c) HEMA26-PES42-HEMA26 and (d) HEMA22- PES34-HEMA22....

......................................................................................................................... 55

 

Figure 2.18. IR Spectra of (a) PES, (b) polyHPMA and (c) HPMA12-PES42- HPMA12... ........................................................................................................ 56

 

Figure 2.19. IR spectra of (a)HPMA12-PES42-HPMA12 and (b) HPMA26- PES42-HPMA26... ........................................................................................... 57

 

Figure 2.20. TGA data for PES and several polyHEMA-co-PES-co-polyHEMA samples heated under air (samples were held at 120 oC until the weight was constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b) HEMA9-PES51- HEMA9, (c) HEMA13-PES42-HEMA13, (d) HEMA26-PES42-HEMA26 and (e) HEMA22-PES34-HEMA22... ........................................................................... 58

 

Figure 2.21. TGA data for PES, polyHEMA and polyHEMA-co-PES-co- polyHEMA samples heated under nitrogen (samples were held at 120 oC until weight was constant (~ 3 hours) before heating at 10 oC/min). (a) PES, (b) polyHEMA, (c) HEMA9-PES42-HEMA9, (d) HEMA13-PES42-HEMA13, (e) HEMA26-PES42-HEMA26 and (f) HEMA22-PES34-HEMA22... .................... 59

 

xii 

Figure 2.22. TGA data for PES and polyHPMA-co-PES-co-polyHPMA samples heated under air (samples were held at 120 oC until the weight was constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b) HPMA12-PES42- HPMA12 and (c) HPMA26-PES42-HPMA26... ............................................... 61

 

Figure 2.23. TGA data for PES and polyHPMA-co-PES-co-polyHPMA samples heated under nitrogen (samples were held at 120 oC until weight was constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b) polyHPMA, (c) HPMA12- PES42-HPMA12 and (d) HPMA26-PES42-HPMA26... ................................... 62

 

Figure 2.24. Room-temperature critical water content (CWC) values of different PES materials in four solvents (NMP, DMF, DMSO, DMAc) (a) Ultrason 2020 P from BASF, (b) Ultrason 6020 P from BASF, (c) Veradel 3600 RP from Solvay, (d) Veradel 3000 RP from Solvay and (e) PES synthesized at MSU Mn=10,000, PDI=2.0. (Each data point is an average from three independent samples, and the data points often obscure the error bars.).. ..........   .................................................................................................................................................... 65  

Figure 2.25. Room-temperature CWC values for several PES samples in NMP. (1) Ultrason 6020P, (2) Veradel 3000RP, (3) Ultrason 2020P, (4) Veradel 3600RP and (5) home-made PES. (Each data point is an average from three independent samples, and the data points often obscure the error bars.).. .........   .................................................................................................................................................... 70  

Figure 2.26. Room-temperature CWC values in NMP for (a) PES, (b) HPMA26 -PES42-HPMA26 and (c) HEMA22-PES34-HEMA22. (Each data point is an average from three independent samples, and the data points often obscure the error bars.).. ............................................................................................... 71

 

Figure 2.27. Proton NMR 500 MHz Spectra of HEMA22-PES34-HEMA22 in DMSO-d6/D2O co-solvents with varying amounts of water... ......................... 73

 

Figure 2.28. DLS size distributions for HEMA22-PES34-HEMA22 (1 mg/mL at 25 oC) dissolved in NMP and NMP/water co-solvents with different volume ratios... ............................................................................................................. 76

 

Figure 2.29. DLS size distributions for HEMA22-PES34-HEMA22 (10 mg/mL at 25 oC) dissolved in NMP and NMP/water co-solvents with different volume ratios... ............................................................................................................. 78

 

xiii 

Figure 2.30. DLS size distributions for HEMA22-PES34-HEMA22 (30 mg/mL at 25 oC) dissolved in NMP and NMP/water co-solvents with different volume ratios... ............................................................................................................. 80

 

Figure 3.1. Schematic diagram of a lithium ion battery containing a metal oxide cathode and a graphite anode. The figure also shows redox reaction during discharge... .................................................................................................... 103

 

Figure 3.2. Concentration polarization during discharge of a lithium ion battery... ......................................................................................................... 104

 

Figure 3.3. Temperature-dependent conductivity of electrolytes containing different fractions of Si-C5NTfLi dispersed in PEGDE-500. These results were obtained by Fadi Asfour, and I repeated some of the measurements... ....................................................................................................................... 108

 

Figure 3.4. Temperature-dependent conductivity of electrolytes containing different fractions of Si-TfMALi dispersed in PEGDE-500. The various fractions of particles (see Table 3.3) lead to the different O/Li ratios shown in the figure... ....................................................................................................................... 110

 

Figure 3.5. Temperature-dependent conductivity for (a) Si-C5NTfLi at O/Li 425 and (b) Si-TfMALi at O/Li 32, both samples contain ~19 wt% modified particles... ....................................................................................................... 111

 

Figure 3.6. Kinetics of step-growth polymerization between dipropargyl and diazido tetraethylene glycol... ........................................................................ 122

 

Figure 3.7. Conductivities of mixtures of LiClO4 with pure PEO (black squares) and triazole-containing PEO (red circles) at different ratios of PEO to LiClO4. The O/Li ratios in the mixture were determined from the masses of LiClO4 and PEO added, and these ratios only include the O atoms from PEO. Measurements occurred at 90 oC... ............................................................... 124

 

Figure 3.8. Conductivities of mixtures of LiClO4 with pure PEO (black squares) and thioether-PEO (red circles) at different ratios of PEO to LiClO4. The O/Li ratios in the mixture were determined from the masses of LiClO4 and PEO added, and these ratios only include the O atoms from PEO. Measurements occurred at 90 oC... ........................................................................................ 125

 

 

xiv 

LIST OF SCHEMES  

   

Scheme 1.1. Structure of the ABA amphiphilic block copolymers synthesized in this study... ..................................................................................................... 2

 

Scheme 1.2. Small molecule model (BisphenolS-I) initiator used to explore ATRP catalytic systems for synthesis of block copolymers. This molecule mimics the structure of PES macroinitiators... ................................................... 2

 

Scheme 1.3. Grafting of polyelectrolytes to nanoparticles to create single-ion conductors... ...................................................................................................... 4

 

Scheme 1.4. Monolayer-modified silica nanoparticles for single ion conductors... ...................................................................................................... 6

 

Scheme 2.1. Chemical Structures of Bisphenol A Polysulfone (PSf) and Polyethersulfone (PES)... ................................................................................ 12

 

Scheme 2.2. Reactions invovled in ATRP... ..................................................... 14

 

Scheme 2.3. Possible architectures of copolymers synthesized from two monomers, A and B... ...................................................................................... 16

 

Scheme 2.4. Structure of the block copolymer synthesized by Jo... ............... 18

 

Scheme 2.5. PSf-based amphiphilic block copolymer prepared by Moore et al. for formation of membranes... .......................................................................... 19

 

Scheme 2.6. PSf-based amphiphilic block copolymers synthesized by Wang el al for use as membrane additives... ................................................................. 20

 

Scheme 2.7. PSf-based graft copolymer prepared by Yi... ............................. 21

 

Scheme 2.8. PES-based graft copolymer synthesized by Yi et al... ............... 21

 

Scheme 2.9. Protocol for making phase-inversion membranes... ................... 25

 

xv 

Scheme 2.10. Selective reaction of triphenylmethyl chloride with the primary alcohol in hydroxypropyl methacrylate mixtures and subsequent isolationof 2-hydroxypropyl methacrylate.......................................................................... 30

 

Scheme 2.11. Synthesis of hydroxyl terminated polyethersulfone (PES)... .... 34

 

Scheme 2.12. Mechanism of etherification in synthesis of PES... .................. 35

 

Scheme 2.13. Synthesis of a macroinitiator from OH-terminated PES... ........ 36

 

Scheme 2.14. Synthesis of BisphenolS-I... .................................................... 37

 

Scheme 2.15. Characteristic protons for calculation of copolymer composition from NMR spectra... ......................................................................................... 85

 

Scheme 2.16. Characteristic protons for calculation of copolymer composition from NMR spectra... ......................................................................................... 86

 

Scheme 3.1. Monolayer modified silica nanoparticle Si-C5NTfLi (silica nanoparticle derivatized with lithiated N-pentenyl triflouromethane sulfonimide)... ................................................................................................. 106

 

Scheme 3.2. Method for determining the Li+ content of PEO-based electrolytes... .................................................................................................. 107

 

Scheme 3.3. Silica nanoparticles prepared by grafting lithiated poly (trifluoromethane sulfonic aminoethyl-methacrylate) (Si-TfMALi) from the surface... ........................................................................................................ 109

 

Scheme 3.4. Proposed qualitative conformations of monolayer Si-C5NTfLi (top) and multilayer Si-TfMALi (bottom) at 30 oC and at 80 oC... ........................... 112

 

Scheme 3.5. Proposed single-ion conductors prepared by synthesis of PEO containing alkene or alkyne groups and subsequent attachment of anions to these groups via click chemistry... ................................................................. 114

 

Scheme 3.6. Polysulfone structures synthesized by Bielawski’s et al for proton-conduction... ....................................................................................... 115

 

xvi 

Scheme 3.7. Polyacrylate structures prepared by Martwiset et al. for formation of membranes that exhibit proton conductivity at 200 oC... ........................... 116

 

Scheme 3.8. Poly(ether ether ketone) prepared by Gao et al for reaction with 3-mercaptopropyltrimethoxysilane via click chemistry... ............................... 117

 

Scheme 3.9. The thioether and triazole structures that result from (a) thiol-ene and (b) alkyne-azido click chemistry, respectively... ..................................... 117

 

Scheme 3.10. (a) Scheme of ideal lithium transport in an electrolyte material and (b) scheme of lithium transport if the click functionality (triazole or thioether) impedes Li+ transport... .................................................................................. 118

 

Scheme 3.11. (a) Monomers synthesized to prepare triazole-containing PEO, (b) monomers to that will react to give sulfur-containing PEO... ................... 119

 

Scheme 3.12. Two methods for synthesis of dipropargyl tetraethylene glycol... ....................................................................................................................... 120

 

Scheme 3.13. Synthesis of several step-growth polymerization monomers via the ditosyl derivative... .................................................................................. 121

 

Scheme 3.14. Synthesis of diallyl tetraethylene glycol.. ............................... 121

 

Scheme 3.15. Step-growth polymerization of diazido and dipropargyl tetraethylene glycol... ..................................................................................... 122

 

Scheme 3.16. Step-growth polymerization of dithiol and diallyl tetraethylene glycol... ........................................................................................................... 123

 

 

 

 

1 

Chapter 1. Introduction

There are two parts to this dissertation: chapter 2 describes the synthesis of

polyethersulfone (PES)-based block copolymers that are relevant to

membrane modification, and chapter 3 explores potential single-ion

conductors based on comb-polyethyleneoxide (PEO) materials. Such

conductors are important elements of lithium ion batteries. Below I briefly

summarize the two projects, and each chapter contains a more extensive

introduction.

Part I: Synthesis of Polyethersulfone (PES)-Based Amphiphilic Block

Copolymers

Polyethersulfone (PES) is widely employed in water-treatment membranes

because of its chemical and thermal stability. However, the hydrophobic nature

of PES may cause severe fouling problems.2 The introduction of ABA block

copolymers (Scheme 1.1) into PES membranes sometimes greatly improves

their filtration properties.3 A PES B block facilitates incorporation into the

membrane, and hydrophilic A blocks can create more wettable surfaces that

resist fouling.

2 

O Om

nhydrophobic block

SO O

O

OH

hydrophilic block

polyethersulfone (PEO)

O Om

OH

poly(hydroxylethyl methacrylate)polyHEMA

poly(2-hydroxylpropyl methacrylate)polyHPMA

Scheme 1.1. Structure of the ABA amphiphilic block copolymers synthesized

in this study. (For interpretation of the references to color in this and all other

figures, the reader is referred to the electronic version of this dissertation.)

 

Scheme 1.2. Small molecule model (BisphenolS-I) initiator used to explore

ATRP catalytic systems for synthesis of block copolymers. This molecule

mimics the structure of PES macroinitiators.

Our synthesis of ABA copolymers relies on ATRP from PES macroinitiators.

To explore atom transfer radical polymerization (ATRP) catalyst systems for

polymerization, BisphenolS-I served as a model compound for the PES

macroinitiator (Scheme 1.2). NMR characterization is much simpler with this

3 

small molecule than a polymer. We tested different combinations of metal

catalyst and ligand, and CuCl/CuCl2/N,N,N′,N′,N′′-pentamethyldiethylene

triamine (PMDETA) proved effective for controlled polymerization of

2-hydroxyethyl methacrylate (HEMA) and 2-hydroxypropyl methacrylate

(HPMA). This catalyst system enabled synthesis of polyHEMA-PES-

polyHEMA and polyHPMA-PES-polyHPMA on a 10-20 g scale. Fourier

transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA)

and 1H NMR show successful synthesis of these block copolymers. Dynamic

light scattering studies reveal copolymer aggregates (radii of 60 nm) in 20 vol%

water in N-methylpyrrolidone. These copolymers may prove valuable in

membrane modification, and we have delivered them to Pall Corporation for

their investigation.

Part II: Synthesis of Comb-Polyethyleneoxide (PEO) via Click Chemistry-

New Polymers for Possible Lithium Ion Conductors 

When a lithium ion battery discharges, electrons flow from the anode to the

cathode through the external circuit. Simultaneously, inside the cell lithium

cations formed at the anode migrate and intercalate into the cathode. Ideally,

lithium ions carry all the current within the cell. Typical values of the Li+

transference number (tLi+, the fraction of the current carried by Li+) in

electrolytes range from 0.2-0.3, however, which indicates the anion is the

dominant species in carrying current. Since a low tLi+ limits a battery’s power

density and often affects the chemical stability of electrolytes, development of

4 

electrolytes with near-unity lithium-ion transference numbers is important.

Scheme 1.3. Grafting of polyelectrolytes to nanoparticles to create single-ion

conductors.1

In research for my MS thesis, I investigated several nanoparticle systems

where Li+ is a counterion to anionic groups immobilized on grafted polymers

(Scheme 1.3). Nanoparticle-containing electrolytes were prepared by mixing

the purified particles and low-molecular weight (~500 g/mol) polyethylene

glycol dimethyl ether (PEGDME-500). Movement of the anions was largely

restricted because of the surface-anchored polymer backbones, so Li+

became the only ion conducting current.

The MS thesis explored four different polymer structures (Scheme 1.3) with

the aim of improving the ionic conductivity of the nanoparticles/PEGDME-500

blend. The first grafted polymer, poly(lithium styrene sulfonate) was initially

synthesized from sodium styrene sulfonate monomer, and lithium exchange

5 

gave poly(lithium sulfonate styrene). In a second case, polyethylene glycol

methyl ether methacrylate (PEGMA) was copolymerized with the styrene

sulfonate, to facilitate transport of lithium cations and increase the miscibility of

the particles with PEGDME-500. The third structure used phosphonates, which

have two lithium counterions per monomer, to increase the lithium content.

The room temperature conductivity of these electrolytes was 10-7

S/cm. This is

several orders of magnitude lower than the conductivity of electrolytes

employed in current lithium ion batteries, and one or two orders of magnitude

lower that current single-ion conductors.

To further improve the conductivity, the fourth structure was inspired by

lithium bis(trifluoromethane sulfonyl) imide (LiTFSI). High conductivity

correlates with the dissociation of Li+ from the anion, and therefore anions such

as ClO4-, PF6

- and bis(trifluoromethylsufonyl amide) (TFSI) are commonly used

in electrolytes. We synthesized a polymerizable analogue of TFSI and grew the

corresponding polymers from silica nanoparticles. The maximum conductivity,

10-6

S/cm, occurred at an oxygen to lithium ratio of 32. The O in this ratio

comes exclusively from ether oxygens in PEGDME-500, and Li comes from the

amount of the lithium cations in the electrolytes. The value of O/Li is a common

measure of the lithium concentration in the electrolytes.

6 

Scheme 1.4. Monolayer-modified silica nanoparticles for single ion

conductors.4

We expected much higher conductivity than 10-6

S/cm, because the

polyelectrolyte constitutes 70~90 wt% of the polymer grafted particles. This

high polyelectrolyte content should supply a large amount of free lithium cations

to contribute to a high conductivity. A previous group member, Fadi Asfour,

investigated monolayer-coated silica nanoparticles as single-ion conductors

(Scheme 1.4), and these materials mixed with PEGDME-500 also have a

conductivity of 10-6

S/cm.4 A possible explanations for the low conductivity with

a dense layer of polyelectrolyte on the particle surface is that not all of the

lithium cations have access to the solvent (PEGDME-500). Most of the

polyelectrolytes are buried near the silica surface and do not contribute to

conductivity.

We then planned to directly modify the PEO structure to obtain a single ion

conductor via alkyne-azido or thiol-ene click chemistry. Chapter 3 describes

synthesis of PEO derivatives with click functionalities in the polymer backbone.

The conductivity with these materials mixed with salts is similar to data with

pure PEO, suggesting that using click chemistry in the synthesis of lithium ion

7 

electrolytes is feasible. The triazole and thioether groups do not limit

conductivity.

8 

 

 

 

 

 

 

 

 

 

 

REFERENCES  

 

9 

REFERENCES

1. Zhao, H. Master Thesis, 2011, MSU.

2. Beyer, M.; Lohrengel, B.; Nghiem, L. D., Membrane fouling and chemical cleaning in water recycling applications. Desalination 2010, 250 (3), 977-981.

3. Zhou, H., Brunelle, J., Moore, D., R., Zhang, L., Misner, M., J., Chen, X., Ma, M., Block copolymer membranes and associated methods for making the same. US Patent, 123033 A1, 2011.

4. Asfour, F. Ph.D Dissertation, 2004, MSU.

10 

Chapter 2. Synthesis of Polyethersulfone (PES)-Based Amphiphilic Block Copolymers

1. Introduction

This chapter describes the synthesis of new polysulfone-based block

copolymers and preliminary studies on their solubility and phase-segregation

properties. To put this work in context, in this introduction I first discuss the

importance of polysulfone materials in water-treatment membranes.

Polysulfone block copolymers can serve as additives to make these

membranes more hydrophilic and reduce fouling. Thus, section 1.2 describes

block copolymers in general, and section 1.3 presents specific literature

examples of the synthesis of polysulfone-based block copolymers. In section

1.4, I provide a brief description of the self-assembly of block copolymers, and

section 1.5 of the introduction mentions a specific application of block

copolymer self-assembly, the formation of nanoporous structures. Finally,

section 1.6 discusses challenges in the self-assembly of polysulfone-based

copolymers.

1.1. Polysulfone Materials and Their Application as Water Treatment

Membranes

Polysulfone (PSf) and polyethersulfone (PES) constitute an important class

of engineering thermoplastics that is widely used to manufacture membranes

with relatively high chemical, thermal and mechanical stability. Broadly

speaking, polysulfone refers to all sulfone-containing polymers, so both

bisphenol A polysulfone and polyethersulfone (PES) are polysulfone materials.

11 

In all polysulfones, but especially PES, the aromatic rings in the polymer

backbone are electronically deactivated by the adjacent sulfone (-SO2) groups.

Additionally, the repeating aromatic rings cause steric hindrance to rotation

around the polymer backbone, and both of these factors make PES unusually

stable.

Bisphenol A polysulfone or poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene

oxy-1,4-phenylene(1-ethylethylidene)-1,4-phenylene) (Scheme 2.1) has a

glass transition temperature (Tg) of around 185 oC. Polyethersulfone (PES) or

poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) has an even higher Tg of 220

oC (Scheme 2.1).

1

Because of its high Tg, PES can retain dimensional stability at temperature

as high as 200 oC.

2 As a high-temperature-resistant resin, PES is also flame

retardant, certified for UL94-V0 (burning stops within 10 seconds on a vertical

specimen; drips of particles allowed as long as they are not inflamed).2

 

12 

Scheme 2.1. Chemical Structures of Bisphenol A Polysulfone (PSf) and

Polyethersulfone (PES).

Membranes made of PES show wide pH tolerance (1 to 13); excellent

resistance to oxidants, including chlorine employed in water treatment (i.e., <

50 ppm); and stability at high temperature (operation at 75 oC and limited

exposure to temperature up to 125 oC).

3  Because of this stability, PES is

widely used to create water treatment membranes for applications such as

wastewater purification and seawater desalination (removal of salt and other

minerals from saline water).

PES shows excellent chemical and water resistance, partly because of its

hydrophobicity. However, this means that it also exhibits a low wettability.

Water contact angles on PES range from 53o to 60

o, and these values are

higher than contact angles on both cellulose (36.9o) and aromatic polyamide

(36.9o) membranes.

4 Recent research correlated low surface wettability with

increased non-specific adsorption of naturally occurring organic matter (NOM)

on the membrane.5 Such adsorption is a major cause of chronic fouling of

membranes during water treatment. Fouling causes a significant increase in

hydraulic resistance and leads to a permanent flux decline or a need for higher

transmembrane pressures.5

Blending of hydrophobic PES with hydrophilic polymers should increase

wettability and decrease fouling propensity.6 However, blends suffer from

long-term instability due to migration of the hydrophilic molecules to the

13 

surface. Amphiphilic block copolymers can potentially increase hydrophilicity

and avoid such instability. The next section describes some general methods

for the synthesis of block copolymers, whereas section 1.3 gives specific

examples of the synthesis of polysulfone-based block copolymers.

1.2. Block Copolymers

The synthesis of block copolymers has been studied extensively, and

several authors reviewed this subject.7 Advances in polymer synthetic

chemistry in recent decades, especially in controlled radical polymerization,

have enabled access to a wide range of block copolymer compositions and

architectures.

In a conventional free radical polymerization, decomposition of an initiator

generates a radical that starts the polymerization of a vinyl monomer (e.g.

methylacrylate, methyl methacrylate and styrene). Because of the high

reactivity of radicals with monomers, propagation is very rapid. Since initiation

is not instantaneous, this rapid propagation makes the lengths of polymer

chains inhomogeneous. Additionally, radicals in solution undergo coupling

reactions that terminate chain growth and further broaden the molecular

weight distribution.

Attainment of narrower molecular weight distributions requires slower

propagation rates and termination reactions through controlled or living

polymerization techniques. Three criteria define such techniques: (1) fast

initiation in which the polymer chains start to propagate at the same time; (2)

14 

homogeneous propagation to ensure that the chains grow at the same rate;

and (3) minimal termination. The case of zero termination corresponds to the

definition of a ‘living’ polymerization. In reality, no system is completely

“living”, but many are highly controlled. Atom Transfer Radical Polymerization

(ATRP) is one of the most common controlled radical polymerization

techniques. Scheme 2.2 shows the ATRP mechanism.8

Scheme 2.2. Reactions invovled in ATRP.8

In this scheme, PnX is the initiating alkyl halide/macromolecular species;

kact is the rate constant of activation through radical formation; kdeact is the

rate constant for the reverse reaction, which gives a dormant chain; Mtm

represents the transition metal species in oxidation state m; and L is the

metal-binding ligand. ATRP uses halide derivatives as initiators (bromo or

chloro groups), and Cu(I) is the most widely used catalyst, although other

metal species such as Ru(II), Fe(II), Cr(III), and Os(II) can also catalyze the

polymerization.9,10

Ligands (typically amine derivatives) chelate the Cu(I) to

increase its solubility in organic solvents and tune its catalytic properties.

Oxidation of the Cu(I)/L complex occurs with homo-cleavage of the carbon

halide bond to form carbon radicals, and the radical initiates the polymerization.

However, kact is typically two to four orders smaller than kdeact, so PnX serves

15 

as a reservoir of radical initiators (Scheme 2.2), and the radical concentration

at any given time is low. The propagation rate is kp[Pn*][M] (kp is the

propagation rate constant, [Pn*] is the concentration of radicals, and [M]

concentration of monomers). Equally important, the termination rate is

kt[Pn*][Pn*] (kt is the termination reaction constant). Thus, the propagation rate

is first order with respect to the radical concentration, but the termination rate is

second order. The low radical concentration gives rise to a slow, controlled

first-order propagation reaction, while the second-order termination reaction is

nearly negligible.

16 

Scheme 2.3. Possible architectures of copolymers synthesized from two

monomers, A and B.

Scheme 2.3 shows the common copolymer structures synthesized from two

types of repeating units, A and B. In linear polymers A and B may appear

randomly, in an alternating pattern or in blocks, and the resulting polymers are

17 

termed random, alternating, and block copolymers, respectively. In some

cases, blocks containing a single repeating unit may branch out from the

polymer main chain to give a graft copolymer. If the blocks branch out from a

common location on the main chain, the structure is a star copolymer. Because

ATRP gives polymers with low polydispersity and minimal termination, it is

particularly useful for synthesizing block copolymers by sequential synthesis of

the different blocks.

Amphiphilic block copolymers contain with both hydrophobic and hydrophilic

blocks. Based on different categories of hydrophilic blocks, there are three

kinds of amphiphilic block copolymers: non-ionic copolymers, such as

poly(ethyleneoxide)-poly(propyleneoxide) (PEO-PPO), poly(ethyleneoxide)-

poly(oxybutylene) (PEO-PBO) and polyethyleneoxide-polystyrene (PEO-PS)

diblock or triblock copolymers; ionic copolymers with polyacrylic acid (PAA) or

polymethacrylic acid (PMAA); and copolymers containing monomers with

nitrogen, such as poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine)

(P4VP), which could be quaternized to provide cationic blocks. Block

copolymer materials are attractive for application as surfactants, foam

stabilizers, flocculants, wetting agents, and dispersants. Micellization of the

amphiphilic block copolymers can solublize active drugs to increase solubility

and circulation half life.11

1.3. Polysulfone-Based Amphiphilic Copolymers

A number of studies examined the synthesis of polysulfone-based

18 

copolymers to modify the properties of polysulfone while retaining aspects of

its high stability. Jo et al. prepared a polysulfone-based amphiphilic block

copolymer for potential use in a fuel cell membrane.12

Nafion (DuPont) is the

most common material for polyelectrolyte membranes in proton exchange fuel

cells, but its conductivity and mechanical stability deteriorate at high

temperature (over 100 oC). Due to its excellent thermal stability, polysulfone

might provide an attractive alternative material, although it is less chemically

stable than Nafion.

hydrophobic

hydrophilichydrophilic

CN

SO3H

p r m-r

(p, m and r are independentintegers, and m is greater than r)

m

hydrophobic block

hydrophilic block

n

SO O

OO

O

 

Scheme 2.4. Structure of the block copolymer synthesized by Jo.12

To prepare a polysulfone-based amphiphilic block copolymer, Jo et al.

copolymerized styrene and acrylonitrile from a polysulfone macroinitiator. They

subsequently partially sulfonated the polystyrene to provide the hydrophilic

block (Scheme 2.4). Because of the high thermal stability of polysulfone,

19 

electrolyte membranes prepared from the amphiphilic block copolymer

maintained their conductivity and mechanical stability at 130 oC.

hydrophobic

hydrophilichydrophilic

hydrophobic block

n

SO O

OO

hydrophilic blocks

9

polyHEMA polyPEGMA polyDMAEMA

OO

OH

m

OO

O

m

OO

N

m

Scheme 2.5. PSf-based amphiphilic block copolymer prepared by Moore et al.

for formation of membranes.13

Moore et al. used polysulfone macroinitiators in polymerization of hydrophilic

monomers such as 2-hydroxyethyl methacrylate (HEMA), polyethylene glycol

methacrylate (PEGMA) and N, N-dimethylaminoethyl methacrylate (DMAEMA)

(Scheme 2.5).13

Synthesis occurred on a 100 g scale, and membranes made

of the synthesized copolymers showed improved hydrophilicity and open pores

that give minimum hydraulic resistance while maintaining the mechanical

strength of PES. The membranes also showed reduced fouling.

Wang et al. synthesized polysulfone-based amphiphilic ABA

copolymerS(Scheme 2.6) using the hydrophilic monomers PEGMA and

20 

3-O-methacryloyl-1,2:5,6-di-O-isopropylidene -D-glucofuranose (MAIpG).14

The protected sugar moiety was acidolysized after polymerization to remove

Scheme 2.6. PSf-based amphiphilic block copolymers synthesized by Wang

for use as membrane additives.14

isopropylidenyl groups and provide the hydrophilic block. They used the

amphiphilic block copolymers as additives to improve the hydrophilicity and

resistance to Bovin Serum Albumin (BSA) adsorption of polysulfone

membranes. In another work, Yi et al. chloromethylated polysulfone

(PSf-CH2Cl, Scheme 2.7), and used the chloromethyl groups to initiate

subsequent ATRP of polyethylene glycol methacrylate (PEGMA) and produce

the amphiphilic graft copolymer.15

21 

Scheme 2.7. PSf-based graft copolymer prepared by Yi.15

Scheme 2.8. PES-based graft copolymer synthesized by Yi et al.16

In a similar work, the same group synthesized a polysulfone-based graft

copolymer using Reversible Addition Fragmentation Chain Transfer (RAFT)

polymerization. In the synthesis of the PES backbone, the ratio of bis

(3-amino-4-hydroxyphenyl) sulfone and bisphenol sulfone was 2/3.16

The

amino group in the synthesized PSf was converted to a RAFT chain transfer

22 

agent, which participated in RAFT polymerization with N,

N-dimethylaminoethyl methacrylate (DMAEMA) or N-isopropylacrylamide

(NIPAAm) hydrophilic monomers to give the amphiphilic graft polymers

(Scheme 2.8).

1.4. Self-assembly of Block Copolymers

When dissolved at low levels in selective solvents, block copolymers tend to

self-assemble into micelles. At even lower concentrations, there are not

enough polymers to self-assemble, so the chains adsorb at the air-water or

aqueous-organic solvent interface. When the copolymer concentration

increases, more and more polymer chains adsorb at the interface until the

concentration reaches a point where both solution and interface are saturated

with polymer chains. Upon further addition of polymer chains to the solution,

the copolymer self-assembles into micelles to reduce the free energy of the

system. The selective solvent is good for only one of the blocks in the

copolymer, so the insoluble blocks aggregate to give the core, while the

soluble blocks form the corona of the micelle. Interaction of the soluble

blocks and the solvent stabilizes the micelles.

Equation (1) expresses the free energy of micellization, ∆G,

∆G =∆H - T∆S (1)

where ∆H and ∆S are the enthalpy and the entropy of micellization. In the

micellization of block copolymers in solution, ∆S is typically negative due to

loss of entropy from localization of polymer molecules in the micelle. Moreover,

23 

the solvent incompatible block is confined to the core, the solvent compatible

block is confined to the corona, and the block copolymer junction is confined to

the interfacial region between core and corona of the micelle. For micellization

of copolymer chains to be a thermodynamically favorable process, the free

energy change of the system upon micellization must decrease, i. e. ∆G<0,

and ∆H must be negative. This readily occurs because the interaction of the

nonselective block with the solvent is unfavorable.

In a molten state or in polymer solutions at high concentrations, block

copolymers can self-assemble into domains with sizes ranging from

nanometer to micrometer scales. The size and structure of the self-assembly is

governed by the polymer molecular weight, the block-size ratio and

temperature. Block copolymers may adopt a disordered/homogeneous state at

high temperature, but when the temperature decreases, the incompatibility of

the constituent blocks increases, because the influence of combinatorial

entropy decreases (T∆S decreases). At the order-to-disorder transition

temperature (TODT), block copolymers form ordered mesophase structures.

TODT depends on the volume fraction of one block, the total number of

monomers in each polymer, and the segmental interaction described by the

Flory-Huggins interaction parameter χ.17,18

24 

Figure 2.1. Equilibrium morphologies in AB diblock copolymers.17

(Used from

ref 17 with permission of Copyright 2012 Annual Reviews.)

Self-consistent mean field theory describes the phase behavior of block

copolymers. As the volume fraction of the A block increases, the microdomain

changes from spheres, cylinders, to gyroid, and finally to lamellae (Figure

2.1).12

In recent years the gyroid phase has attracted attention because of its

potential application in ionic conductive materials. While the matrix provides

mechanical support, the bicontinuous gyroid phase can act as an ionically

conductive channel.19 ,20

1.5. Block Copolymers as Phase Inversion Membrane Materials

Phase-inversion has been widely used in the preparation of asymmetric

filtration membranes since the 1960s.21,22,23

(Asymmetric membranes

contain a dense surface layer on a highly porous support of the same material.)

Scheme 2.9 shows a typical phase-inversion process. Polymer materials are

dissolved in a good solvent, such as tetrahydrofuran (THF),

dimethylformamide (DMF), N-methylpyrrolidone (NMP) that is also miscible

25 

with water. The concentration of the polymer is normally in the range of 20 to

35 wt% to maintain a high viscosity. The polymer solution is then cast on a

glass substrate and solvent is allowed to evaporate for a short time (10

seconds to 1 minute). Finally, the substrate is immersed in a nonsolvent bath

(typically water) at a pre-determined temperature. After oven drying, the film is

detached from the substrate.

Scheme 2.9. Protocol for making phase-inversion membranes.

The exchange between solvent and nonsolvent introduces phase separation

in the polymer layer, which leads to an asymmetric porous polymer membrane

structure. Figure 2.2 shows the morphologies of phase-inversion membranes

made from polysulfone materials. Because of the rapid solvent exchange near

the membrane surface, the thin top layer is a structure of closely packed

viscous polymer solution

cast on substrate

allow the solvent topartially evaporate

immerse in a nonsolvent bath

dry the film

26 

polymeric spheres and serves as the functional layer for the separation

process. The much thicker bottom structure with large elongated voids

(macrovoids) provides the mechanical support, but little resistance to flow in

comparison to the skin layer.14

Figure 2.2. Phase inversion membranes made from PSf14

(upper left: SEM

top view, upper right: edge view, NMP solvent), and PES16

(bottom: SEM edge

view DMAc solvent), (used with permission of Elsevier from references 14 and

16, copyright )

When the membrane material is a block copolymer, the above-mentioned

phase-inversion process can lead to structures that contain uniform nanopores

in their interfacial layer. The most successful studies employed poly

(styrene)-block-poly (4-vinylpyridine) (PS-b-P4VP).24,25

This asymmetric

membrane forms in a combination of phase-inversion and block copolymer

self-assembly. In an appropriate solvent, the block copolymer self-assembles

27 

into perpendicularly aligned cylinders at the membrane surface, because this

is the thermodynamic equilibrium structure. When the membrane is immersed

into the nonsolvent coagulation bath, solvent-nonsolvent exchange occurs

immediately at the membrane surface to lock in the thermodynamic equilibrium

structure (perpendicularly aligned cylinder morphology) at the interface. In

contrast, the nonsolvent migrates slowly into the interior of the membrane, and

the delayed solvent-nonsolvent exchange gives a non-equilibrium structure,

similar to that in a conventional phase-inversion membranes. The narrow

surface pore size distribution may lead to relatively sharp molecular weight

cutoffs (Figure 2.3), whereas the minimal thickness of the interfacial layer can

allow extremely high flux. In a recent publication, Peinemann and coworkers

reported a remarkable flux of 890 L m-2

h-1

bar-1

through such membranes.24

Figure 2.3. SEM images of membranes prepared by phase inversion of

poly(styrene)-co-poly(4-vinylpyridine). Peinemann’s work. Edge view (left), top

view (right). 24

(Used with permission from ref 24, Copyright 2007 Nature

Publishing Group.)

1.6. Unique Aspects of Self Assembly of Polysulfone-based Block

Copolymers

28 

We synthesized ABA triblock copolymers where the B block is PES and the

A block is poly(2-hydroxyethyl methacrylate) (polyHEMA) or poly(2-hydroxy

propyl methacrylate) (polyHPMA). We note that these copolymers present

some unique features for self assembly. First, the PES block will have a

relatively broad molecular weight distribution. Most of the previous research in

block copolymer self assembly focused on model compound such as

PPO-PEO and PS-PAA because those polymers are easy to synthesize with a

narrow polydispersity index (PDI). The PDI value is the ratio of weight-average

to number-average molecular weight (Mw/Mn). With polysulfone-based

copolymers, a narrow PDI is difficult to achieve because polysulfones are

obtained via polycondensation chemistry, which leads to a PDI of around 2.

Although ATRP can give relatively monodisperse polyHEMA and polyHPMA,

the condensation polymerization of PES will lead to a more polydisperse

material. However, a recent study shows that narrow dispersity copolymers are

not required for periodic nanoscale assembly. Widin and coworkers examined

the self assembly of poly(styrene)-poly(1,4-butadiene)- poly(styrene) ABA

triblock copolymers similar in structure to those described here.26

Their ABA

triblock copolymers contained a narrow dispersity A block (Mw/Mn ≤ 1.05)

and a variable dispersity B block (Mw/Mn= 1.18−2.00). These copolymers

show the same ordered structures regardless of the polydispersity of the B

block, although the composition window for different ordered structures varies

with PDI. We expect that if the PDI of a synthesized copolymer is below 1.5,

29 

one can still achieve periodic nanoscale self-assembly.

A second unique feature of PES-containing block copolymers is that PES is

more rigid than PS and other well-studied hydrophobic polymer structures in

the literature. The persistence length of this rigid polymer backbone will thus

be larger than common PS and PMMA blocks, which have has a flexible

backbone and coil structure. The extent to which rigidity will alter self-assembly

is unknown.

2. Results and Discussion

This section primarily describes the synthesis of several ABA block

copolymers where PES is the hydrophobic B block and polyHEMA or

polyHPMA serves as the hydrophilic A block. The first section describes

purification of HPMA to obtain a single isomer for formation of polyHPMA

blocks. Subsequent sections present the synthesis of PES and conversion of

PES to a macroinitiator for polymerization of HEMA or HPMA. A model

compound for the PES macroinitiator, BisphenolS-I (see below) is used to

develop an appropriate ATRP catalytic system to synthesize block copolymers.

Finally, we synthesized copolymers with a range of compositions. The new

block copolymers are characterized using nuclear magnetic resonance (NMR)

spectroscopy, gel permeation chromatography (GPC), Fourier transform

infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and dynamic

light scattering (DLS). Measurements of critical water content (CWC), which is

used to study the hydrophilicity of PES and synthesized block copolymers in

30 

solvent/nonsolvent (water) mixtures, clearly show there is an apparent

increase of hydrophilicity for the block copolymer. NMR spectroscopy and DLS

indicate the formation of micellar structures.

2.1. Purification of Hydroxypropyl Methacrylate (HPMA) Isomers

Hydroxypropyl methacrylate (HPMA) was purchased from Acros Organics,

as an approximately 3:1 (2-hydroxypropyl methacrylate/1-hydroxypropan-2-yl

methacrylate) mixture of the primary and secondary alcohols. The secondary

alcohol (2-hydroxypropyl methacrylate) is the major product, and most

commercially available HPMA has a similar composition.

OO

OH

OO

OH

+Ph3CCl

Et3N, 50 oC,

overnight

OO

OCPh3

+O

O

OH

VacuumDistillation

OO

OH

2-hydroxypropylmethacrylate

1-hydroxypropan-2-ylmethacrylate

2-hydroxypropylmethacrylate

Scheme 2.10. Selective reaction of triphenylmethyl chloride with the primary

alcohol in hydroxypropyl methacrylate mixtures and subsequent isolationof

2-hydroxypropyl methacrylate.

31 

Purification of the isomers starts with reaction of the mixture with

triphenylmethyl chloride (Scheme 2.10). The bulky triphenylmethyl group

selectively protects the primary alcohol to allow isolation of 2-hydroxypropyl

methacrylate by vacuum distillation. Triethylamine is a good base for this

reaction, and in a typical purification process, 14.4 g of the isomer mixture

gave 4.2 g of pure monomer.

32 

Figure 2.4. 1H NMR 500 MHz spectra of an HPMA isomer mixture (bottom)

and purified 2-hydroxypropyl methacrylate (top) in CDCl3.

The 1H NMR spectra in Figure 2.4 show that before purification, signals from

protons on both isomers appear. After purification, only signals from

2-hydroxypropyl methacrylate are present. Peaks in the bottom spectrum

33 

around 2.5 and 3.6 ppm correspond to the hydroxyl protons in the two isomers.

The upper spectrum clearly demonstrates disappearance of the signals from

1-hydroxypropan-2-yl methacrylate and the successful purification of

2-hydroxypropyl methacrylate from the isomer mixture.

2.2. Synthesis of PES with Hydroxyl End Groups

ID Monomer (mmol)

Base Solvent Temperature

(oC)

Mn/PDIc

A B C

1 20 / 20 K2CO3 DMF 150 4,500/2.1

2 20 / 20 K2CO3 DMSO 180 5,200/1.9

3 20 / 20 KF DMSO 180 3,800/1.8

4 20 / 20 K2CO3 DMSO/Toluene 160 5,500/2.0

5 20 / 20 K2CO3 Sulfolane 220 4,700/1.8

6 20 / 20 K2CO3 DMAc/Toluene 140 7,800/1.8

7 / 20 20 K2CO3 DMAc/Toluene 140 10,800/2.0d

8 / 20 20 K2CO3 DMAc/Toluene 140~170 14,700/2.1d

aMonomer A: bis(4-chlorophenyl) sulfone B: bis(4-fluorophenyl) sulfone

C: 4,4’-sulfonydiphenol

bReaction time: 24h

cDetermined using GPC with polystyrene samples.

dWe did not consider signals from large aggregates in calculating these

values.

Table 2.1. Different conditions for synthesis of PES and the molecular weights

and PDI values of the resulting polymer.a,b

34 

Table 2.1 shows the different conditions used to synthesize polyethersulfone

(PES). 4,4’-sulfonylbisphenol (bisphenol S, monomer C) is reacted with

bis(4-chlorophenyl) sulfone (monomer A) or bis(4-fluorophenyl) sulfone

(monomer B) in a dipolar aprotic solvent at high temperature (up to 285 oC),

e.g., Scheme 2.11. K2CO3 or Na2CO3 generate phenate salts ‘in situ’. In a

typical poly-condensation, the highest PDI of the final polymer product is

around 2.0, but in most of the commercial products the PDI is as high as 4.0. A

possible explanation for the lower polydispersity in our polymers is that low

molecular weight oligomers are added to improve the rheology and processing

properties in the commercial formulation. Table 2.1 shows that reactions using

bis(4-fluorophenyl) sulfone give higher molecular weights than reactions with

bis(4-chlorophenyl) sulfone.

 

Scheme 2.11. Synthesis of hydroxyl terminated polyethersulfone (PES).

The weight-average molecular weights of the synthesized polymers (Mw)

35 

are 20,000~30,000 and the PDIs are ~2 (Table 2.1). Weight average molecular

weights are always higher than number average values (Mn). Compared to

commercial PES, the synthesized PES has similar molecular weight and a

lower PDI. To ensure that the chains terminate in phenol groups, we reacted

the polymers with excess amount of 4,4’-sulfonydiphenol after chain formation

(Scheme 2.11). In this way we were eventually able to cap both ends with an

ATRP initiator and form ABA block copolymers. An SNAr mechanism is used to

describe the etherification chemistry between bisphenol sulfone and

Nu-

F-+

SO O

FF

SO O

NuF

SO O

FF Nu

Scheme 2.12. Mechanism of etherification in synthesis of PES.

bishalophenyl sulfone. The nucleophile in Scheme 2.12 represents a

bisphenolate that attacks the bishalophenyl sulfone to give an anion

intermediate, which in the final step goes through reductive elimination to yield

the ether product.27

The first step is generally quite slow and is rate

determining, so any structure that facilitates the nucleophilic attack would give

a higher reaction rate. This may explain why reactions using bis(4-fluorophenyl)

sulfone give higher molecular weights than reactions with bis(4-chlorophenyl)

36 

sulfone.

2.3. Synthesis of a PES Macroinitiator and Use of a Model Compound to

Explore the ATRP Catalytic System

 

Scheme 2.13. Synthesis of a macroinitiator from OH-terminated PES.

To synthesize PES macroinitiator (Scheme 2.13), hydroxyl terminal groups

are allowed to react with bromoisobutyryl bromide. The resulting PES

macroinitiator bears the bromoisobutyryl structure, which can initiate

polymerization of HEMA or HPMA. Before moving on to the synthesis of block

copolymers using this macroinitiator, we performed the reaction in Scheme

2.13. The purpose of this reaction is two-fold: first, to confirm that the reaction

conditions for esterification yield an essentially quantitative reaction. In the

synthesis of PES, we used an excess of bisphenol sulfone to ensure a phenol

end group structure at both ends, but we must also convert all of these phenol

end groups to the ester structure to synthesize the ABA block copolymer.

Second, the product of the reaction in Scheme 2.14 (BisphenolS-I) served as

a model compound to explore the chemistry to polymerize HEMA and HPMA

blocks. BisphenolS-I is synthesized with two equivalents of bromoisobutyryl

bromide and one equivalent of bisphenol sulfone in acetone in less than 3

hours, and the yield of this reaction is typically higher than 97%.

Br

OBr

SO O

OHHO

SO O

OO

OBr

OBr

Et3N, Acetone+

BisphenolS-I

Scheme 2.14. Synthesis of BisphenolS-I.

Figure 2.5. 1H NMR 500 HMz spectra of bisphenol sulfone (bottom) and

BisphenolS-I (top) in DMSO-d6. The signal at 2.5 ppm is due to DMSO-d6.

38 

Figure 2.5 shows the 1H NMR spectra of bisphenol sulfone and

BisphenolS-I. Upon reaction with bromoisobutyryl bromide, chemical shifts of

the aromatic protons change from 7.70 ppm (Ha) and 6.90 ppm (Hb) to 8.10

ppm and 7.45 ppm, and a new peak at 2.0 ppm corresponds to the methyl

groups of the bromoisobutyryl end group. This result shows that the conditions

for esterification of the phenol groups are nearly quantitative and should also

work for the polymer. Unfortunately, the large number of repeat units in the

polymer make direct characterization of PES derivatization by NMR difficult.

 

Figure 2.6. ATRP kinetic plot for polymerization of HEMA using BisphenolS-I

39 

as an initiator and CuBr/PMDETA as the catalyst in DMF, the initial monomer

concentration was 2 M.

As an analogue compound for the PES macroinitiator with the

bromoisobutyryl functionality on both sides, BisphenolS-I allowed us to

explore ATRP catalytic systems for HEMA polymerization. Since the PES

macroinitiator is only soluble in polar solvents such as DMF, DMSO, DMAc and

NMP, polymerization must also occur in theses solvents. BisphenolS-I was

used to polymerize HEMA, using CuBr/PMDETA (N,N,N′,N′,N′′-pentamethyl

diethylene triamine) as a catalyst, and NMP as the solvent at 40 °C. Some

prior polymerizations of methacrylate monomers using macroinitiators

occurred at 90-110 °C, but we did not use high temperatures to avoid

auto-polymerization of the monomers. Figure 2.6 shows the polymerization

kinetics for the CuBr/PMDETA/NMP system. Polymerization occurred rapidly

during the first 30 min and then slowed suggesting significant termination of

the propagating chains. The fast polymerization rate at initial stages might be

due to the use of the CuBr catalyst, since C-Br bonds have a lower

dissociation energy than C-Cl bonds and potentially gives a faster and less

controlled ATRP kinetics.28

The low conversion of monomers is also a problem,

especially when using macroinitiators, since we desire the synthesis of block

copolymers with high hydrophilic content.

40 

Figure 2.7. ATRP kinetic plot for polymerization of HEMA using ethyl

bromoisobutyrate as an initiator and CuCl/CuCl2/PMDETA as the catalyst in

NMP, the initial monomer concentration was 2 M.

To further explore ATRP of HEMA, we examined polymerization using a

simple conventional initiator, ethyl bromoisobutyrate (Figure 2.7). We

employed CuCl as a catalyst instead of CuBr, because the higher dissociation

energy of the C-Cl (relative to C-Br) bond could give slower kinetics, as

mentioned above. Additionally, 0.5 equivalents of CuCl2 were added to slow

down and control the reaction. This polymerization was conducted as a

small-scale reaction. The kinetic plot in Figure 2.7 indicates that with the

41 

conventional initiator ATRP of HEMA is controlled with this catalyst system.

The final conversion of the reaction is as high as 97% after 24 hours. With a

controlled ATRP catalytic system in hand, we decide to use the model initiator

BisphenolS-I to further test the controlled character of this polymerization

chemistry. Using BisphenolS-I as the initiator, we employed a Cu(I)/Cu(II)

Figure 2.8. ATRP kinetic plot for polymerization of HEMA using ethyl

BisphenolS-I as the initiator and CuCl/CuCl2/PMDETA as the catalyst in NMP,

the initial monomer concentration was 2 M.

ratio of 1/1 to further decrease the reaction rate, considering that there are two

initiating sites for each BisphenolS-I molecule. The kinetic plot in Figure 2.8

42 

shows that this reaction gives a final conversion of around 96% at 24 hours,

but it may still show a small slope decrease (some termination of

polymerization) at around 100 minutes. Nevertheless, we felt that with the high

conversion and reasonable reaction kinetics, these polymerization conditions

were sufficient to proceed with HEMA polymerization from the macroinitiator.

2.4. Polymerization from a PES Macroinitiator

Figure 2.9. ATRP kinetic plot for polymerization of HEMA using a PES

macroinitiator and CuCl/CuCl2/PMDETA as the catalyst in NMP, the initial

monomer concentration was 1.3 M.

43 

The kinetic plot in Figure 2.9 shows that polymerization kinetics are well

controlled (the plot is linear) when using a macroinitiator. The reaction reaches

92% conversion after 24 hours. Ideally to get a block copolymer with a desired

hydrophilic block content, we could stop the polymerization at the time

(determined from Figure 2.9) required for sufficient conversion of the

hydrophilic monomer. In practice, we employ NMR spectroscopy to monitor the

conversion in each reaction.

(a)

Figure 2.10. 1H NMR 500 MHz spectra of (a) NMP

44 

Figure 2.10 (cont’d)

(b)

(c)

Figure 2.10. 1H NMR 500 MHz spectra of (a) NMP, (b) HEMA26-PES42-

HEMA26 and (c) macroinitiator in DMSO-d6.

Figure 2.10 shows 1H NMR spectra of the polymerization solvent NMP,

45 

HEMA26-PES42-HEMA26 and macroinitiator. The macroinitiator spectrum

(Figure 2.10c) shows a signal from the termini of the initiator structure (Hc), but

this peak is too weak to deduce molecular weight. Comparison of spectra (a)

and (b) shows that the small peaks at 1.9, 2.2, 2.7 and 3.3 ppm in the

copolymer spectrum correspond to residual NMP solvent. This high-boiling-

point solvent is nearly impossible to remove from theses amphiphilic

copolymers. Nevertheless, the spectrum of the copolymer (Figure 2.10b)

contains the expected characteristic signals from both PES and polyHEMA

blocks. The Ha and Hb signals stem from the aromatic protons in PES,

whereas the He peak results from the methyl groups in the polymerized

methacrylate structure These three sets of peaks are separated from other

peaks in the spectrum and allow us to quantify the block copolymer

composition. The ratio of polyHEMA repeat units to PES repeat units is simply

1/3 the area for the He peak divided by 1/4 the areas of the Ha or Hb peak. We

then used the Mn value of the PES block (determined from GPC) to calculate

an approximate composition of the copolymer.

46 

Polymer Samples Scale (g)Mn of the

starting PES (GPC)

Mn

(NMR)

Mn

(GPC)

PDI (GPC)

HEMA9-PES51-HEMA9 10 11,900 14,300 19,800 1.7

HEMA13-PES42-HEMA13 14 9,650 13,000 19,600 1.6

HEMA26-PES42-HEMA26 18 9,650 16,300 23,100 1.4

HEMA22-PES34-HEMA22 15 7,800 13,600 19,200 1.4

HPMA12-PES42-HPMA12 18 9,650 13,000 21,900 1.4

HPMA26-PES42-HPMA26 12 9,650 17,100 24,900 1.5

*End group signals were too weak to determine the PES Mn value from NMR

spectra. The NMR Mn values assume that the PES molecular weight is that

determined from GPC.

Table 2.2. Block Copolymers with their Molecular Weights and PDI Values.

Table 2.2 shows all the PES-based ABA block copolymer samples

synthesized in this work, including 4 samples of polyHEMA-co-PES-co-

polyHEMA and 2 samples of polyHPMA-co-PES-co-polyHPMA. By optimizing

the ATRP catalytic system in the previous section, we synthesized the

copolymer on a scale of 10~20 g. To clarify the nomenclature of the

copolymers, PES indicates the middle block (B block) is composed of

polyethersulfone and HPMA or HEMA means that the A block is composed of

47 

either polyHPMA or polyHEMA. The number after PES is number of PES

repeating units in the B block, determined from GPC analysis of the

synthesized PES samples; the number after HPMA or HEMA indicates the

repeating units in theses blocks as determined from the NMR integration data

for the copolymer. Appendices 1 to 6 contain the NMR spectra for all the block

copolymers.

2.5. GPC Analysis of HEMAn-PESm-HEMAn and HPMAn-PESm-HPMAn

Block Copolymers

Figure 2.11. Gel-permeation chromatograms of (a) PES51 and (b) the

copolymer HEMA9-PES51-HEMA9.

Figure 2.11 shows gel-permeation chromatograms curves of PES and

HEMA9-PES51-HEMA9. Curve a, which is the chromatogram of the PES

48 

precursor used to synthesize HEMA9-PES51-HEMA9, shows a major peak

corresponding to Mn of 11,900. The small peak at around 5.5 min suggests a

Mn of 1,000,000, which corresponds to a small amount of aggregation of PES

polymers in DMF. Curve b, the chromatogram of HEMA9-PES51-HEMA9,

exhibits a major peak corresponding to an Mn of 19,800. Thus the Mn of the

polymer increased from 11,900 to 19,800 upon addition of the HEMA blocks.

This suggests that the molecular weight of each polyHEMA block is 3,450, but

9 units of HEMA have a molecular weight of only 1170. We used DMF as the

GPC solvent and polystyrene chains as standards, and previous studies

suggest that the molecular weights of poly-methacrylate polymers are

exaggerated by a factor of two in this GPC condition.29

This along with

possible differences in PES and HEMA9-PES51-HEMA9 aggregation may

account for the difference between the calculated GPC and NMR values for

the length of the polyHEMA blocks.

49 

Figure 2.12. Gel-permeation chromatograms of (a) PES42 (b) copolymer

HEMA13-PES42-HEMA13 and (c) HEMA26-PES42-HEMA26.

HEMA13-PES42-HEMA13 and HEMA26-PES42-HEMA26 were synthesized

from the same PES precursor, which exhibits an Mn value of 9,650 based on

the GPC peak centered around 7.6 min (Figure 2.12a). This precursor polymer

also shows an aggregation peak at around 5 min in the chromatogram, and we

did not use this peak in calculating the molecular weight. The major peaks from

the unaggregated copolymers (Figure 2.12b and 2.12c) appear at smaller

elution times than for the precursor, consistent with the expected increases in

molecular weight. The copolymers also show large aggregation peaks at

smaller elution times, and surprisingly the size of the aggregation peaks

increases with the amount of HEMA in the polymer. Thus, with an increase in

the hydrophilic content, more aggregation occurs. Mn values calculated based

on the unaggregated peaks in Figure 2.12 increase from 9,650 for the PES

50 

precursor to 13,000 and 16,300 for HEMA13-PES42-HEMA13 and

HEMA26-PES42-HEMA26, respectively. As mentioned above, these values

likely grossly overestimate the amount of HEMA in the polymer.

Figure 2.13. Gel-permeation chromatograms of (a). PES34 and (b). HEMA22-

PES34-HEMA22.

HEMA22-PES34-HEMA22 was synthesized from the PES with a molecular

weight of 7,800 (PES34), and has the highest hydrophilic content of any of the

polyHEMA-containing copolymer, 46.2 wt% polyHEMA. Figure 2.13 shows that

the major GPC peak for this copolymer shifts to a smaller elution time relative

to the precursor, indicating a molecular weight increase from 7,800 to 13,600.

Despite the high hydrophilic content of this copolymer, we did not observe

significant aggregate peaks, probably because of the relatively low molecular

weight of the PES.

51 

Step-growth polymerizations, such as the synthesis of PES, typically yield

PDI values around 2.0. As expected, the overall PDI decreased after formation

of the copolymer (Table 2.2) because polyHEMA grown by ATRP has PDI

values near 1.0. Also, increasing the polyHEMA content lowers the PDI of the

final copolymer. 1.7 for HEMA9-PES51-HEMA9, 1.6 for HEMA13-PES42-

HEMA13, 1.4 for HEMA26-PES42-HEMA26 and 1.3 for HEMA22-PES34-

HEMA22. Equation (2) was used to correlate the PDIs of each block, with the

PDI of the entire block copolymer. 30   

PDIAB=ωA2(PDIA-1)+ωB

2(PDIB-1) + 1 (2)

In this equation, PDIAB is the PDI of the copolymer, ωA and PDIA are the

weight fraction and PDI of the A block, and ωB and PDIB are the weight

fraction and PDI of the B block.

Figure 2.14. An ABA block copolymer with monodisperse A block and

polydisperse (PDI=2.0) B blocks.

52 

Polymer Sample PDI from GPCCalculated PDI

via equation (3)

HEMA9-PES51-HEMA9 1.7 1.79

HEMA13-PES42-HEMA13 1.6 1.69

HEMA26-PES42-HEMA26 1.4 1.49

HEMA22-PES34-HEMA22 1.4 1.41

Table 2.3. PDIs of various copolymers as determined from GPC data or

calculated using equation (2).

Using equation (2), and assuming the polyHEMA blocks are monodisperse

(PDIA=1.0), we calculated the PDIs of the four polyHEMA-co-PES-co-

polyHEMA samples (Table 2.3). In the calculation, we used PDI values from

GPC for the PES block. The calculated and experimental results match very

well for each sample.

53 

Figure 2.15. Gel-permeation chromatograms of (a) PES42, (b) HPMA12-

PES42-HPMA12 and (c) HPMA26-PES42-HPMA26.

Similar to copolymers with HEMA, Figure 2.15 shows that the

HPMA12-PES42-HPMA12 and HPMA26-PES42-HPMA26 copolymers have

increased molecular weights compared to PES, with the major peak shifted to

smaller elution times. Aggregation peaks also appear for these copolymers.

As mentioned above, GPC with polystyrene standards gives much higher

molecular weights than NMR analysis.

2.6. Infrared Spectra of the Block Copolymers

54 

Figure 2.16. IR spectra of (a) PES, (b) polyHEMA and (c) HEMA22-

PES34-HEMA22.

Figure 2.176 shows IR spectra of PES, polyHEMA and the copolymer

HEMA22-PES34-HEMA22. In the spectrum of PES, sulfone groups (SO2) give

rise to strong antisymmetric (1369-1290 cm-1

) and symmetric (1170-1120 cm-1

)

stretching modes. The PES backbone contains para--substituted benzene

structures that show an absorption maximum around 817 cm-1

due to the

out-of-plane CH bending. Although the PES we prepared has phenol end

groups, there are not corresponding OH stretching bands between 3500 and

3200 cm-1

. Because the phenol only exists at the chain terminus, the small

amount of phenol groups does not give a strong signal in the IR spectrum.

In the IR spectrum of polyHEMA, the hydrogen-bonded OH stretching mode

of the hydroxyl group in HEMA repeating units gives rise to a strong broad

55 

band between 3500 and 3200 cm-1

; the CH2 antisymmetric stretch appears

between 2940 and 2915 cm-1

; the strong C=O stretching band shows up near

1750 cm-1

, and the symmetric C-O-C stretch at low frequency absorbs

between 1160 and 1000 cm-1

. The IR spectrum of HEMA22-PES34-HEMA22 is

essentially a sum of the PES and polyHEMA spectra.

Figure 2.17. IR spectra of (a) HEMA9-PES51-HEMA9, (b) HEMA13-PES42-

HEMA13, (c) HEMA26-PES42-HEMA26 and (d) HEMA22-PES34-HEMA22.

Figure 2.17 shows IR spectra of the four polyHEMA-co-PES-co-polyHEMA

copolymer samples synthesized in this work. The fraction of polyHEMA in the

copolymer increases from a to d. In each sample, the spectrum contains

characteristic signal s from both PES (1369-1290 cm-1

and 1170-1120 cm-1

from sulfone groups, 817 cm-1 from para-substituted benzene structures) and

polyHEMA (strong broad band between 3500 and 3200 cm-1 from hydroxyl

56 

groups, 1750 cm-1

from C=O carbonyl groups) blocks. The four spectra were

normalized using the peak at 817 cm-1

, which corresponds to the out-of-plane

CH bending on the para-substituted benzene structure in the PES block. On

going from spectrum a to d, that intensity of the broad peak between 3500 and

3200 cm-1

(OH strectch of HEMA), and the absorbance at 1750 cm-1

(C=O

stretch in HEMA) increase, reflecting increasing polyHEMA content.

Figure 2.18. IR Spectra of (a). PES, (b). polyHPMA and (c). HPMA12-PES42-

HPMA12.

Figure 2.18 presents the IR spectra of PES, polyHPMA and

HPMA12-PES42-HPMA12. Similar to polyHEMA, In the IR spectrum of

polyHPMA, the hydroxyl group gIves rise to a strong broad band between

3500 and 3200 cm-1

; the CH2 antisymmetric stretch leads to a band between

2940 and 2915 cm-1

; the C=O stretching band appears near 1750 cm-1

, and

the symmetric C-O-C stretch at low frequency absorbs between 1160 and

57 

1000 cm-1

. The IR spectrum of HEMA12-PES42-HEMA12 is essentially a sum

of the PES and polyHPMA spectra as expected.

 

Figure 2.19. IR spectra of (a)HPMA12-PES42-HPMA12 and (b) HPMA26-

PES42-HPMA26.  

Figure 2.19 shows IR spectra of the two polyHPMA-co-PES-co-polyHPMA

copolymer samples synthesized in this work. As with polyHEMA-co-PES-co-

polyHEMA, the two spectra were normalized using the peak at 817 cm-1

,

which corresponds to out-of-plane CH bending on the para-substituted

benzenes in the PES block. The intensity of the broad peak between 3500 and

3200 cm-1

(hydroxyl group in HPMA) and the C-O stretch (1750 cm-1

) are

larger for the copolymer containing more HPMA, consistent with the NMR

characterization.

2.7. TGA of the Block Copolymers

58 

Figure 2.20. TGA data for PES and several polyHEMA-co-PES-co-polyHEMA

samples heated under air (samples were held at 120 oC until the weight was

constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b). HEMA9-PES51-

HEMA9, (c) HEMA13-PES42-HEMA13, (d) HEMA26-PES42-HEMA26 and (e)

HEMA22-PES34-HEMA22.

Figure 2.20 shows TGA of PES and the five polyHEMA-co-PES-co-

polyHEMA copolymers heated under air. In each case, the sample was held at

120 oC for around 3 hours before starting the heating. All polyHEMA containing

copolymers, show a three-stage weight loss. The weight loss before 250 oC

probably corresponds partly to loss of the NMP, which could not be removed

from the copolymer. In the second stage, the weight loss between 250 and 500

oC corresponds to degradation of the polyHEMA block. The final stage of

weight loss between 500 and 700 oC results from degradation of the PES block,

as the PES sample (curve a) shows major degradation only in this temperature

59 

region. In all samples, the weight loss curve ends at zero weight retention,

which indicates that there is almost no residual metal catalyst (copper) in the

copolymer. The fraction of polyHEMA in the copolymers increases from b

through e, so the fraction of the weight loss that occurs from 500 to 700 oC

decreases from b through e because of the lower PES content when samples

contain more polyHEMA.

 

Figure 2.21. TGA data for PES, polyHEMA and polyHEMA-co-PES-co-

polyHEMA samples heated under N2 (samples were held at 120 oC until

weight was constant (~ 3 hours) before heating at 10 oC/min). (a) PES, (b)

polyHEMA, (c) HEMA9-PES42-HEMA9, (d) HEMA13-PES42-HEMA13, (e)

HEMA26-PES42-HEMA26 and (f) HEMA22-PES34- HEMA22.

Figure 2.21 shows TGA of the five polyHEMA-co-PES-co-polyHEMA

copolymers and PES heated under N2. In each case, the sample was held at

60 

120 oC for around 3 hours before starting the heating scan. Curve a is the

weight loss of pure PES, which eventually carbonizes under nitrogen and has

a final weight retention of around 40 wt%. This PES sample was synthesized in

the lab and has a Mn of 10,000 and a PDI of 2.0. TGA of of pure polyHEMA

(curve b) shows a complete weight loss before 550 oC, and the major

degradation occurs between 350 and 550 oC. The polyHEMA sample was

synthesized via free radical polymerization, and GPC analysis shows Mn =

57,400 and PDI = 3.6. For the polyHEMA-co-PES-co-polyHEMA copolymers,

based on the TGA of pure PES and polyHEMA, all of the polyHEMA in the

copolymer should be gone at the end of the analysis, and the PES content

should have 40% weight retention. Accordingly, the PES content should be the

final weight retention divided by 0.4, and polyHEMA and residual solvent

should make up the rest of the polymer.

Sample polyHEMA content from

NMR polyHEMA content from

TGA*

HEMA9-PES51-HEMA9 11.0 wt% 15.4 wt%

HEMA13-PES42-HPMA13 17.0 wt% 16.7 wt%

HEMA26-PES42-HEMA26 30.0 wt% 33.3 wt%

HEMA22-PES34-HEMA22 46.2 wt% 53.0 wt%

*Calculations are described in experimental section.

Table 2.4. PolyHEMA Content in Copolymer Samples as Calculated from NMR

61 

Spectra and TGA under N2.

Table 2.4 shows the compositions of the four polyHEMA-co-PES-co-

polyHEMA samples as calculated from both NMR and TGA. The results from

the two characterization techniques are quite consistent.

 

Figure 2.22. TGA data for PES and polyHPMA-co-PES-co-polyHPMA

samples heated under air (samples were held at 120 oC until the weight was

constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b) HPMA12-

PES42-HPMA12 and (c) HPMA26-PES42-HPMA26.

Figure 2.22 shows TGA curves of the two polyHPMA-co-PES-co-polyHPMA

copolymers and PES heated under air. As mentioned above, curve a shows a

two-stage degradation of PES. The two polyHPMA-containing copolymers

show a similar 3-stage weight loss pattern to polyHEMA-co-PES-co-

polyHEMA. In all samples, the TGA curve ends at zero weight retention, again

indicating that there is little residual metal catalyst (copper) in the copolymer

62 

sample. The fraction of polyHPMA in the copolymers increases from b to c, so

the fraction of the weight loss that occurs from 500 to 700 oC decreases from b

to c because of the lower PES content when samples contain more

polyHPMA.

Figure 2.23. TGA data for PES and polyHPMA-co-PES-co-polyHPMA

samples heated under N2 (samples were held at 120 oC until weight was

constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b) polyHPMA, (c)

HPMA12-PES42-HPMA12 and (d) HPMA26-PES42-HPMA26.

Figure 2.23 shows TGA of PES, polyHPMA and polyHPMA-co-PES-co-

polyHPMA with heating under N2. Curve b shows that the weight loss of pure

polyHPMA is complete before 550 oC. The polyHPMA sample was synthesized

via free radical polymerization, and GPC analysis shows Mn = 34,646 and PDI

= 1.8. As mentioned above, PES retains 40% of its weight, presumably due to

carbonization. Thus, similar to polyHEMA-co-PES-co-polyHEMA, we can

63 

determine the fraction of polyHPMA in the copolymers from the final weight

retention in the TGA.

Sample polyHPMA content from

NMR polyHPMA content from

TGA

HPMA12-PES42-HPMA12 26.3 wt% 33.5 wt%

HPMA26-PES42-HPMA26 43.3 wt% 43.0 wt%

*Calculations are described in experimental section.

Table 2.5. PolyHPMA Content in Copolymer Samples as calculated from NMR

spectra and TGA.

Table 2.5 shows the calculated compositions of the two polyHPMA-co-

PES-co-polyHPMA samples, as determined from NMR and TGA data. Again,

the results from the two characterization techniques are reasonably consistent.

2.8. Critical Water Content (CWC) Values of PES and PES-based Block

Copolymers

In one process to prepare micelles using amphiphilic block copolymers, the

copolymers are first dissolved in a good solvent for both blocks, for example N,

N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), N, N-dimethyl

acetamide (DMAc) or methylpyrrolidone (NMP). In a subsequent step,

deionized water is added slowly and the quality of the resulting co-solvent for

the PES block gradually decreases. At a certain level of water, the PES blocks

start to associate/aggregate to form micelles in the solution and the solution

becomes visually turbid. This transition is abrupt, and I further stirred the

64 

mixture for another 30 min to make sure the turbidity maintains. The fraction of

deionized water at which the micellization process starts is defined as the

critical water content (CWC).25,26

Sample Source Mwa PDI

Terminal

Structureb

Ultrason 2020P BASF 27,000-37,000 2.5-3.0 OMe, Cl

Ultrason 6020P BASF 46,000-55,000 3.0-4.0 OMe, Cl

Ultrason E 2020P

SR Micro BASF 45,000 3.0 OH, Cl

Veradel 3600 RP

Solvay 21,000 3.0 OH, Cl

Veradel 3000 RP

Solvay 43,000-50,000 3.0 OH, Cl

aValues from GPC characterization

bCharacterized using titration by

suppliers

Table 2.6. Commercial Polyethersulfones and their Molecular Weights, PDI

Values and Terminal Groups.

Although CWC is characteristic micellization for the block copolymers, for

pure PES, the CWC corresponds to the point where the polymer separates

from the mixture. The CWC of the hydrophobic block (PES) plays a major role

in the block copolymer micellization process. Figure 2.24 shows the

room-temperature (20 oC) CWC data for five different PES materials: Ultrason

2020P, Ultrason 6020P, Veradel 3600RP, Veradel 3000RP and home-made

PES in four different solvents (NMP, DMF, DMSO, DMAc). Table 2.6 presents

the composition of the commercial polymers, and the PES we synthesized has

65 

terminal hydroxyl groups, a molecular weight (Mn) of 10,000 and a PDI of 2.0.

(a). (1) DMSO, (2) DMF, (3) DMAc, (4) NMP.

(b) (1) DMSO, (2) DMF, (3) DMAc, (4) NMP.

Figure 2.24. Room-temperature critical water content (CWC) values of

different PES materials in four solvents (NMP, DMF, DMSO, DMAc).

66 

Figure 2.24 (cont’d)

(c) (1) DMSO, (2) DMF, (3) DMAc, (4) NMP.

(d) (1) DMSO, (2) DMF, (3) DMAc, (4) NMP.

67 

Figure 2.24 (cont’d)

(e) (1) DMSO, (2) DMF, (3) DMAc, (4) NMP.

As Figure 2.24 shows, there is a linear relation between CWC data and the

logarithm of the polymer concentration, which can be written as equation (3)

CWC = -Alogc0 + B (3)

where c0 is the initial copolymer concentration and A and B are constants for a

specific copolymer. At the critical water content, the value of the copolymer

concentration is the critical micelle concentration if micellization occurs. Figure

2.24 shows that in each polymer sample, the order of CWC values in different

organic solvents is NMP>DMAc>DMF>DMSO. This could be explained by the

solubility parameters in Table 2.7. The solubility parameter (δ) gives a

numerical estimate of the degree of interaction between materials and is a

good indicator of solubility. Materials with similar values of δ are more likely to

be miscible.

68 

Solvent δd (MPa

1/2) δ

p (MPa

1/2) δ

h (MPa1/2

) δ (MPa1/2

)

NMPa 18.0 12.3 7.2 22.9

DMFa 17.4 13.7 11.3 24.8

DMSOa 18.4 16.4 10.2 26.6

DMAca 16.8 11.5 10.2 22.7

Watera 15.5 16.0 42.4 47.9

PSu (Udel)a 19.3 0 7.0 20.3

PESb 19.6 10.8 9.2 24.2

polyHEMAc 15.1±0.7 11.9±0.3 18.8±0.4 26.9±0.5

a. Brandrup, J.; Immergut, E. H.; Grulke, E. A. Polymer Handbook, 4th

ed.,

vol. 3. New York: Wiley-Interscience; 1999.

b. Hansen, C. M. Hansen Solubility Parameters: A User’s Handbook, 2nd

ed., Boca Raton, Fla: CRC Press; 2007.

c. Caykara, T.; Ozyurek, C.; Kantoglu, O.; Guven, O. J. Polym. Sci. B:

Polym. Phy. 2002, 40, 1995-2003.

Table 2.7. Solubility Parameters of Several Solvents and Polymers at 25 oC.

There are three components that contribute to a total solubility parameter: a

dispersion force component (δd), a hydrogen bonding component (δh) and a

polar component (δp). The square of the overall solubility parameter (δ) is the

sum of the squares of the component solubility parameters.

δ2 = δd

2 + δh2 + δp

2

Table 2.7 shows the solubility parameters of solvents and polymers used in

69 

this study. Both NMP (δ=22.9 MPa1/2

) and DMAc (δ=22.7 MPa1/2

) have lower

solubility parameter than PES (δ=24.2 MPa1/2

). Initially, addition of water

(δ=47.9 MPa1/2

) will increase the co-solvent solubility parameter, making it

closer to that of PES and increasing solubility of PES in the co-solvent.

However, further addition of the water will increase the solubility parameter of

the co-solvent beyond that of PES to decrease PES solubility. DMF (24.8

MPa1/2

) has a solubility parameter that is very close to PES (24.4 MPa1/2

), so

addition of water only decreases the PES solubility in DMF; DMSO (26.6

MPa1/2

) has a larger solubility parameter than PES and thus this solvent

requires the least amount of water to precipitate PES.

Figure 2.25. Room-temperature CWC values for several PES samples in NMP.

(1) Ultrason 6020P, (2) Veradel 3000RP, (3) Ultrason 2020P, (4) Veradel

3600RP and (5) home-made PES. (Each data point is an average from three

70 

independent samples, and the data points often obscure the error bars.)

Figure 2.25 compares CWC values of different polymers in NMP. The CWC

values decrease in the order home-made PES>Veradel 3600RP>Ultrason

2020P>Veradel 3000RP>Ultrason 6020P. CWC depends on temperature, the

nature of the organic solvent, and polymer concentration and molecular weight.

Veradel 3600RP and Ultrason 2020P have similar molecular weights that are

smaller than those of Veradel 3000RP and Ultrason 6020P, so Veradel

3600RP and Ultrason 2020P have larger CWC values than Veradel 3000RP

and Ultrason 6020P. Most of the termini in Veradel polymers are OH, whereas

Ultrason polymers have OMe and Cl terminal groups. The larger portion of OH

end groups increase the CWC of Veradel polymers relative to Ultrason when

molecular weights are equal. Our synthesized PES has a low PDI (~2) relative

to the commercial available materials (PDI=3~4). The broad molecular weight

distribution in the commercial polymers means that a portion of the sample has

very high molecular weight and this fraction of the polymer chains should

precipitate most readily from water/organic co-solvents. Thus the CWC value

is smaller for the commercial polymers than for our PES.

71 

Figure 2.26. Room-temperature CWC values in NMP for (a) PES, (b)

HPMA26-PES42-HPMA26 and (c). HEMA22-PES34-HEMA22. (Each data point

is an average from three independent samples, and the data points often

obscure the error bars.)

Figure 2.26 shows room-temperature CWC data for the pure PES,

HPMA26-PES42-HPMA26 and HEMA22-PES34-HEMA22 in NMP. Both

copolymers have higher CWC values than PES, due to the higher

hydrophilicity of the copolymers. Although HPMA26-PES42-HPMA26 has a

similar hydrophilic polymer content (43.3 wt% polyHPMA) to HEMA22-PES34-

HEMA22 (46.2 wt% polyHEMA), it has smaller CWC values than HEMA22-

PES34-HEMA22. HPMA and HEMA differ only by a methyl group, but HEMA is

a more hydrophilic monomer than HPMA.

2.9. Aggregation of Block Copolymers in Dilute Solutions—NMR and DLS

Studies

72 

The previous sections show that we can successfully synthesize

polyHEMA-co-PES-co-polyHEMA and polyHPMA-co-PES-co-polyHPMA ABA

block copolymers on scales of 10-20 g. Moreover, the block copolymers

precipitate or form micelles upon addition of water to organic solvents. In the

following discussion, we use HEMA22-PES34-HEMA22 to study the copolymer

aggregation behavior in solvents that are selective for one of the blocks.

Initially, a good solvent (DMSO-d6 in NMR studies, NMP in DLS studies) for

both hydrophobic and hydrophilic blocks is dissolves the polymer, and then we

add water to induce aggregation of the block copolymer. Since PES is the

hydrophobic block, water/DMSO or water/NMP co-solvents will selectively

dissolve the polyHEMA block.

1H NMR spectroscopy can conveniently reveal aggregation. Because the

PES block aggregates while the polyHEMA remains dissolved, signals from

PES should decrease with increasing water content while signals from

polyHEMA should remain relatively constant.

73 

 

Chemical Structure of HEMA22-PES34-HEMA22

 

DMSO-d6   

 

DMSO-d6/D2O 19:1 (volume ratio)

Figure 2.27. 1H NMR 500 MHz Spectra of HEMA22-PES34-HEMA22 in

DMSO-d6/D2O co-solvents with varying amounts of water.

74 

Figure 2.27 (cont’d)

 

DMSO-d6/D2O 9:1 (volume ratio) 

 

DMSO-d6/D2O 4:1 (volume ratio)

Figure 2.27 shows the NMR spectra of HEMA22-PES34-HEMA22 in

DMSO-d6 or mixtures of DMSO-d6 and D2O with different volume ratios. The

peaks between 0.7 and 0.9 ppm (He) are the characteristic signals of methyl

groups in polymerized methacrylate monomers, so all of the four spectra are

normalized using this peak whose integral is set to 3.0. The two peaks at

75 

7.2-7.5 ppm (Hb) and 7.8-8.1 ppm (Ha) stem from the aromatic protons in the

PES block, and each of the these peaks should correspond to 4 protons per

repeat unit.

Solvent (v/v) Integral of He

(polyHEMA)

Integral of Hb

(PES)

Integral of Ha

(PES)

DMSO-d6 3.0 2.71 2.62

DMSO-d6/D2O (19/1) 3.0 2.16 2.26

DMSO-d6/D2O (9/1) 3.0 0.75 0.84

DMSO-d6/D2O (4/1) 3.0 0.30 0.40

Table 2.8. Evolution of the 1H NMR signals from HEMA22-PES34-HEMA22

with increasing of D2O content in the DMSO-d6 solvent. See the structure in

Figure 2.27 for proton assignments. Signals were normalized to that of He.

Table 2.8 shows integrals of three sets of peaks obtained with co-solvents at

different ratios. Clearly, as the D2O content in the solvent increases, NMR

signals corresponding to the PES block decrease, presumably because the

PES block aggregates to form the core of a micelle. The semi-solid state

micelle core loses its NMR sensitivity due to magnetic gradients, dipolar

broadening, and slow relaxation in the micelle core. The hydrophilic polyHEMA

block, on the other hand, form the corona part of the micelle and stays mostly

solvated. The signal to noise ratios in the NMR spectra are similar in pure

DMSO-d6, DMSO-d6/D2O (19:1) and DMSO-d6/D2O (9:1), because the

76 

copolymer is quite soluble in these three different co-solvents. However, when

the D2O content increases to 20% by volume, the copolymer become insoluble

and the signal to noise ratio in the spectrum declines. Visually the NMR

solution in the tube also becomes turbid.

DLS provides values for the sizes of aggregates in solution. Because of the

high CWC values (Figure 2.24), we selected NMP/water co-solvents to study

the aggregation behavior over a wide range of water contents.

HEMA22-PES34-HEMA22 was first dissolved in NMP, and deionized water was

added dropwise to reach desired NMP/water ratio. The solution was further

stirred for 30 min before DLS characterization.

Figure 2.28. DLS size distributions for HEMA22-PES34-HEMA22 (1 mg/mL at

25 oC) dissolved in NMP and NMP/water co-solvents with different volume

ratios.

77 

Solvent

(v/v)

Radii at

Peak 1 (nm)

Volume % of aggregates

In Peak 1

Radii at

Peak 2

(nm)

Volume % of aggregates

In Peak 2

NMP 3.7 99.8% X X

NMP/water (19/1)

4.9 99.8% X X

NMP/water (9/1)

7.1 96.5% X X

NMP/water (4/1)

59.6 34.7% 2,581 65.3%

Table 2.9. DLS particle sizes and particle volume percentages for aggregates

of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures

contained 1 mg/mL HEMA22-PES34-HEMA22.

Figure 2.28 and Table 2.9 show the particle size distributions that form in

mixtures containing 1 mg/mL of HEMA22-PES34-HEMA22 in NMP/water

co-solvents. The particle size distribution in pure NMP (curve a, Figure 2.28)

shows a single peak centered around 3.7 nm. This corresponds to a fully

dissolved polymers, since NMP is a good solvent for both PES and polyHEMA

blocks. Curve b shows the size distribution when the polymer is dissolved in

NMP/water (with a 19/1 volume ratio). With this small amount of water, the

solvent mixture is still a good solvent for the copolymer, so the DLS

measurement shows a fully dissolved state with monomodal radii centered

around 4.9 nm. At a water content of 10 % by volume (curve c, Figure 2.28),

the copolymer remains solvated, but the most common particle radii increases

to 7.1 nm. As the solvent becomes poorer and some molecules begin

78 

interacting, the dissolved molecule sizes increases by a factor of two on going

from pure NMP to NMP with at 10 vol% water. Below 10 vol% water, a few

aggregates with radii of 1,000-2,000 nm also exist, but they constitute less

than 5 vol% of the total aggregates. Finally when the water content reaches 20

vol% (curve d, Figure 2.28), all of the copolymer form micelles with a bimodal

size distribution. Aggregates with radii centered around 59.6 nm and 2,000 nm

account for 34.7 vol% and 65.3 vol% of the particles, respectively.

Figure 2.29. DLS size distributions for HEMA22-PES34-HEMA22 (10 mg/mL at

25 oC) dissolved in NMP and NMP/water co-solvents with different volume

ratios.

79 

Solvent

(v/v)

Radii at

Peak 1 (nm)

Volume % of aggregates

In Peak 1

Radii at

Peak 2 (nm)

Volume % of aggregates

In Peak 2

NMP 3.6 99.8% X X

NMP/water (19/1)

4.0 100% X X

NMP/water (9/1)

5.9 96.3% X X

NMP/water (4/1)

56.3 100% X X

Table 2.10. DLS particle sizes and particle volume percentages for aggregates

of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures

contained 10 mg/mL HEMA22-PES34-HEMA22.

Figure 2.29 and Table 2.10 show the particle size distributions that form in

mixtures containing 10 mg/mL of HEMA22-PES34-HEMA22 in NMP/water

co-solvents with different volume ratios. Even at this polymer concentration,

the copolymer is fully dissolved in pure NMP solvent and NMP with 5 vol% and

10 vol% water. The particle sizes are essentially the same as in mixtures with 1

mg/mL HEMA22-PES34-HEMA22 (compare Tables 2.9 and 2.10). Finally when

the water content reaches 20 vol% (curve d, Figure 2.29), the particle radii

center around 56 nm. We are not sure why the higher polymer concentration

leads to a monomodal size distribution while the 1 mg/mL solution shows a

bimodal size distribution in 20 vol% water. The higher polymer concentration

may lead to a higher concentration of micelles, which overwhelms the signals

from a few large aggregates.

80 

Figure 2.30. DLS size distributions for HEMA22-PES34-HEMA22 (30 mg/mL at

25 oC) dissolved in NMP and NMP/water co-solvents with different volume

ratios.

Solvent

(v/v)

Radii at

Peak 1 (nm)

Volume % of aggregates

In Peak 1

Radii at

Peak 2 (nm)

Volume % of aggregates

In Peak 2

NMP 2.9 100% X X

NMP/water (19/1)

2.8 100% X X

NMP/water (9/1)

5.8 94.5% X X

NMP/water (4/1)

61.3 100% X X

Table 2.11. DLS particle sizes and particle volume percentages for aggregates

of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures

contained 30 mg/mL HEMA22-PES34-HEMA22.

Figure 2.30 and Table 2.11 show the particle size distribution in mixtures

81 

containing 30 mg/mL of HEMA22-PES34-HEMA22 in NMP/water co-solvents

with different volume ratios. The size distributions are essentially the same as

those with 10 mg/mL HEMA22-PES34-HEMA22, although the radii are a little

smaller with 5 vol% water. Most notably, regardless of the copolymer

concentrations (1 mg/mL, 10 mg/mL or 30 mg/mL), the aggregated state with

20 vol% water content contains micelles with a radii around 60 nm.

3. Conclusion

ABA block copolymer samples were synthesized on of 10~20 g scale,

including 4 samples of polyHEMA-co-PES-co-polyHEMA and 2 samples of

polyHPMA-co-PES-co-polyHPMA. Using a model compound 4,4'-sulfonylbis

(4,1-phenylene) bis(2-bromo-2-methyl-propanoate) as initiator, we selected

CuCl/CuCl2/PMDETA in NMP as the catalytic system for the polymerization of

HEMA and HPMA monomers from PES macroinitiators. FT-IR spectra, TGA

and 1H NMR spectra show successful synthesis of these block copolymers.

Critical Water Content (CWC) studies demonstrate that the hydrophilicity of

synthesized copolymers increases with the amount of polyHEMA or polyHPMA

in the block copolymers as expected. Both DLS and 1H NMR studies show that

addition of non-solvent (water) to the copolymer solution causes aggregation

of the block copolymer, particularly the PES block. DLS indicates that with 20

vol% water micellar the aggregates have radii of 60 nm, regardless of the

copolymer concentration. Such copolymers may prove useful in modification of

polysulfone membranes.

82 

4. Experimental Section

4.1. Materials

Phthalimide, potassium derivative (500 g, 99%, Acros Organics),

triethylamine (J. T. Baker), N, N, N’, N’, N’’-pentamethyldiethylenetri amine

(PMDETA, Aldrich, 99%), 4-fluorophenyl sulfone (100 g, 99%, Acros Organics),

4, 4’-sulfonyldiphenol (500 g, 98%, Aldrich), bis(4-chlorophenyl) sulfone (500 g,

98%, Aldrich), α-bromoisobutyryl bromide (500 g, 98%, Aldrich), N,

N-dimethylacetamide (2.5 L, 99%, Alfa Aesar), 1-methyl-2-pyrrolidinone (4 L,

ACS grade, 99.0+%, Alfa Aesar), postassium carbonate (500 g, ACP

Chemicals), 4-(dimethylamino) pyridine (100 g, 99% prilled, Aldrich), sulfolane

(500 mL, Kodak) and pyridine (500 mL, ACS grade ≥99%, CCI Chemical) were

used as received. Cu(I)Br (99.999%, Aldrich) was purified using a saturated

aqueous NaBr solution. Hydroxypropyl methacrylate (1 kg, 97+%, mixture of

isomers, stabilized, Acros Organics), 2-Hydroxyethyl methacrylate (500 mL,

200-220 ppm monomethyl ether hydroquinone as inhibitor, Aldrich, 97%) were

passed through a basic alumina column before use. ULTRASON E 6020P

(100 g), E 2020 P (100 g) and 2020P SR Micro (100 g) were received as free

samples from BASF. Veradel 3000 RP and Veradel 3600 RP were received as

free samples from Solvay Specialty Polymers. Aluminum oxide (1 kg, activated,

basic, ~150 mesh, 58 Å, Aldrich) was heated in an oven overnight at 120 oC for

activation.

4.2. Characterization

83 

1H NMR and

13C NMR spectra were collected using a Varian UnityPlus-500

spectrometer using the residual proton signals from the solvent as the

chemical shift standard. Thermogravimetric analysis (TGA) were carried out in

air or under N2 using a Perkin-Elmer TGA 7 instrument at a heating rate of 10

oC/min. Samples were held at 120

oC until the weight stabilized (~3 h) before

starting the heating process. FTIR spectra were collected with a Mattson

Galaxy 300 spectrometer. FTIR samples were made by mixing the polymer

with KBr and forming pellets. DLS studies were carried out on a Malvern

Zetasizer Nanoseries ZEN3600 instrument at 30 oC.

Standards and Conditions of Gel Permeation Chromatography (GPC)

Analysis

This GPC instrument contains Water 1515 Isocratic HPLC Pump, Water 717

Plus Autosampler, Waters 2414 Refractive Index Detector and Water 2487

Dual λ Absorbance Detector. This instrument uses DMF as solvent and PLgel

10 μm mixed-B as column, 70 oC at column and 50

oC at RI detector. DMF

was used as the eluting solvent at a flow rate 1 mL/min, and monodisperse

polystyrene standards were used to calibrate the molecular weights. The

concentration of the polymer solutions used for GPC measurements was 1

mg/mL.

84 

Standard

PSI

Elution time (min) 6.3 7.1 7.7 8.4

Molecular weight (Mn) 401,340 45,730 12,860 2,727

PSII

Elution time (min) 5.9 6.8 7.4 8.3

Molecular weight (Mn) 931,780 95,800 24,150 3,680

Table 2.12. Polystyrene standards used to calibrate the results of GPC in

DMF.

The molecular weight and PDI of each polymer sample were determined

by GPC. Two sets of polymer standards, PSI and PSII, were employed and

results are shown in Table 2.12. The effective calibration range for GPC

analysis is between 5.9 min (Mn of 931,780) and 8.4 min (Mn of 2,727).

Calculation of polyHEMA content in Copolymers Using TGA and NMR

Data

The polyHEMA content from TGA was calculated using Equation (4),

(4)

where W120~300 is the weight loss between 120 and 300 oC (we assume this

mostly corresponds to the unremoved solvent in the copolymer sample) and

Wretention is the final weight retention of the sample. The value of Wretention

should exclusively come from the PES block, since pure PES has a weight

retention of around 40%, whereas polyHEMA and polyHPMA show no weight

85 

retention at the end of TGA.

Based on integration of the proton peaks in NMR, we obtained polyHEMA or

polyHPMA and PES contents in the copolymer.

 

Scheme 2.15. Characteristic protons for calculation of copolymer composition

from NMR spectra.  

As shown in Scheme 2.15, to calculate polyHEMA content from 1H NMR, we

compared signals from protons in the methyl groups from methacrylate (Ha, 3

protons per repeating units, 0.7~0.9 ppm), with signals from the aromatic

protons at the ortho position to sulfone group (Hb, 4 protons per repeating unit,

7.4~7.5 ppm). Based on integrations of these two sets of peaks, polyHEMA

content could be calculated according to equation (5).

                                                    (5)

Where IHa is the integral of NMR peaks at 0.7-0.9 ppm (the molecular weight of

the HEMA repeating unit is 130 g/mol) and IHb is the integral of the NMR peak

at 7.4-7.5 ppm (the molecular weight of the PES repeating unit is 232 g/mol).

Calculation of polyHPMA content in Copolymers Using TGA and NMR

Data

86 

The polyHPMA content from TGA was calculated using Equation (4). Similar

to polyHEMA-containing copolymers, NMR could also be used to obtain the

polyHPMA content.

 

Scheme 2.16 Characteristic protons for calculation of copolymer composition

from NMR spectra.

As shown in Scheme 2.16, polyHPMA gives signals from methyl groups (Ha)

from methacrylate at 0.7-0.9 ppm, as well as from the side-chain methyl group

(Ha’) at 0.9-1.2 ppm. The integration of the combined peaks corresponds to 6

protons. We compared this integral with that for the aromatic protons at the

ortho position (Hb) to the sulfone group (4 protons per repeating unit, 7.4-7.5

ppm). Based on integrations of these sets of peaks, we calculated the

polyHPMA content according to equation (6).

                                                        (6)

IHa+Ha’ is the integral of the NMR peaks from 0.7-1.1 ppm (the molecular

weight of the HPMA repeating unit is 144 g/mol) and IHb is the integral of the

NMR peak at 7.4-7.5 ppm (the molecular weight of the PES repeating unit is

232 g/mol).

87 

Synthesis of PES with Hydroxyl End Groups. Bisphenol sulfone (26.00 g,

0.104 mol) and bisfluorophenyl sulfone (26.92 g, 0.104 mol 1:1 molar ratio)

were added to a 500 mL 3-neck flask charged with N, N-dimethylacetamide

(240 mL) and toluene (100 mL). Potassium carbonate (2 equivalents, 0.21 mol)

was added, and then the solution was purged with nitrogen for 30 min. The

reaction was heated to 145 °C, and a Dean-Stark trap attached to the flask

removed residual water from the reactor. After 12 hours at 145 °C, bisphenol

sulfone (1 g, 4 mmol) was added to the solution to cap the polymer with

phenolic groups, and after an additional hour the polymer was precipitated by

addition into 4M HCl. The white precipitate was dispersed in boiling methanol

(350 mL) for 4 hours to extract residual monomer and salts from the polymer.

The polymer was recovered by filtration, and the extraction was repeated with

fresh methanol. After drying under vacuum at 60 °C overnight, the product was

a white fine powder, and 48 g of product was isolated (99% yield).

Synthesis of the PES Macroinitiator. Polyethersulfone (50 g, 5 mmol end

groups, calculated using molecular weight from GPC assuming hydroxyl end

groups) was dissolved in a mixture of DMF/DMSO (400 mL, 1:1 volume). After

the polymer was dissolved, 20 equivalents of triethylamine (10.1 g, 0.1 mol)

and bromoisobutyryl bromide (22.9 g, 0.1 mol) were added at 0 °C. The

solution was heated to 60 °C and stirred with a mechanical stirrer for 24 hours.

Upon addition to 4 M aqueous HCl, the macroinitiator precipitated as a gel.

After poring off the solvent, the product was immersed in 300 mL boiling

88 

methanol (sometimes more than once), and after 4h, the gel-like material

solidified. The solid material was broken into small particles, and methanol

extraction was performed two times using a Soxhlet extraction setup. After

the final wash, the product was a fine light yellow powder. The product was

dispersed in 400 mL deionized water at 60 °C and vigorously stirred for 1 h

before filtration, this dispersion-filtration process was repeated twice before the

solid was dried under vacuum at 60 °C overnight.

Synthesis of 4,4'-sulfonylbis(4,1-phenylene) bis(2-bromo-2-methyl-

propanoate) (BisphenolS-I). In a 100 mL round bottom flask, 2.55 g

bisphenol sulfone (0.01 mol) and 2.1 g triethylamine (0.021 mol) were added to

50 mL dry acetone. The flask was put on an ice bath to give a solution

temperature of around 0 °C. Bromoisobutyryl bromide (2.7 mL, 0.022 mol) was

added to the solution slowly through a septum (typical addition time is around 5

min). Large amounts of white/light yellow salts formed in the course of addition.

After the addition, the ice bath was removed and the solution was allowed to

warm to room temperature. After 2 h at room temperature, 50 mL of

deionized water was added to dilute the reaction solution, and the product was

extracted with dichloromethane (3 x 40 mL). The combined dichloromethane

layer was washed with deionized water (3 x 30 mL), dried with magnesium

sulfate, and the solvent was removed using rotary evaporation. The white solid

was dried in vacuum to give 5.2 g (96% yield).

Purification of 2-Hydroxypropyl Methacrylate. A 200-mL round bottom flask

89 

was charged with 14.4 g commercial hydroxypropyl methacrylate isomer

mixture (0.1 mol), 27.8 g trityl chloride (0.1 mol), 10.1 g triethylamine (0.1 mol)

and 300 mL acetone. The solution was heated to 50 °C in an oil bath and

allowed to react overnight. Solvent and residual triethylamine were removed

by rotary evaporation, and vacuum distillation at 90 °C at 80 mtorr gave the

unreacted secondary alcohol isomer (4.2 g, yield 29.2%).

Synthesis of ABA block copolymers: polyHEMA-co-PES-co-polyHEMA.

In a 250 mL Schlenk flask, the PES macroinitiator (15 g, 1.5 mmol), HEMA (20

g, 0.154 mol) and PMDETA (0.60 mL, 2.9 mmol) were dissolved in NMP (120

mL). (The stirred mixture occasionally required heating to obtain a

homogeneous solution.) After two freeze-pump-thaw cycles, the flask was

refilled with nitrogen, CuCl2 (0.108 g, 0.8 mmol) was added and the solution

was stirred until the Cu species dissolved. After two freeze-pump-thaw

cycles, the flask was refilled with nitrogen and CuCl (0.078 g, 0.8 mmol) was

added to the flask under N2. The flask was heated in a 40 °C oil bath. The

reaction was monitored by 1H NMR and when the polymerization reached the

desired HEMA conversion, the solution was opened to the air to quench

polymerization reaction. The polymer was precipitated by addition of the

solution into 300 mL of saturated disodium ethylenediaminetetraacetate (EDTA)

solution, and the copolymer was recovered as a fine powder. Suction filtration

required 5-6 hours to recover the product. The air-dried product was dissolved

in DMSO, precipitated in water, and after a second precipitation from DMSO,

90 

the polymer was dried under vacuum at 90 °C for 24 h. Synthesis of

polyHPMA-co-PES-co-polyHPMA occurred similarly.

Free Radical Polymerization of Hydroxyethyl Methacrylate (HEMA). A

Schlenk flask was charge with 15 mL dry THF, 4 g of HEMA (0.031 mol) and

0.43 g azobisisobutyronitrile (2.6 mmol). After one freeze-pump-thaw cyle, the

flask was put onto a 70 °C oil bath. After an overnight reaction, NMR

spectroscopy of the reaction solution showed that the conversion was 100%,

and the flask was opened to air to quench the reaction. PolyHEMA precipitated

onto the bottom of the flask, and the solid product was dried under vacuum at

70 °C. 3.56 g product was recovered (90% yield).

 

 

 

 

 

 

 

 

91 

 

 

 

 

 

 

 

 

 

 

APPENDIX A  

 

92 

 

 

 

Appendix A1. 1H NMR 500 MHz spectrum of HEMA9-PES51-HEMA9 in

DMSO-d6.

93 

 

Appendix A2. 1H NMR 500 MHz spectrum of HEMA13-PES42-HEMA13 in

DMSO-d6.

94 

 

Appendix A3. 1H NMR 500 MHz spectrum of HEMA26-PES42-HEMA26 in

DMSO-d6.

95 

 

Appendix A4. 1H NMR 500 MHz spectrum of HEMA22-PES34-HEMA22 in

DMSO-d6.

96 

 

Appendix A5. 1H NMR 500 MHz spectrum of HPMA12-PES42-HPMA12 in

DMSO-d6.

97 

Appendix A6. 1H NMR 500 MHz spectrum of HPMA26-PES42-HPMA26 in

DMSO-d6.

98 

 

 

 

 

 

 

 

 

 

 

 

REFERENCES  

99 

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radical polymerization. Progress in Polymer Science 2010, 35 (8), 959-1021. 11. Owen, S. C.; Chan, D. P. Y.; Shoichet, M. S., Polymeric micelle stability. Nano Today 2012, 7 (1), 53-65. 12. Jo, W. H. K., T.; Hwang, I. C.; Kwon, N. H. Novel amphiphilic block copolymer, method for manufacturing the same and polymer electrolyte membrane using the same. 2010. 13. Zhou, H., Brunelle, Daniel, J., Moore, D., R., Zhang, L., Misner, M., J., Chen, X., Ma, M., Block copolymer membranes and associated methods for making the same. US Patent, 123033 A1, 2011. 14. Wang, J. Y.; Xu, Y. Y.; Zhu, L. P.; Li, J. H.; Zhu, B. K., Amphiphilic ABA copolymers used for surface modification of polysulfone membranes, Part 1: Molecular design, synthesis, and characterization. Polymer 2008, 49 (15), 3256-3264. 15. Yi, Z. A.; Zhu, L. P.; Xu, Y. Y.; Zhao, Y. F.; Ma, X. T.; Zhu, B. K., Polysulfone-based amphiphilic polymer for hydrophilicity and fouling-resistant modification of polyethersulfone membranes. Journal of Membrane Science 2010, 365 (1-2), 25-33. 16. Yi, Z.; Zhu, L. P.; Cheng, L.; Zhu, B. K.; Xu, Y. Y., A readily modified polyethersulfone with amino-substituted groups: Its amphiphilic copolymer synthesis and membrane application. Polymer 2012, 53 (2), 350-358. 17. Bates, F. S.; Fredrickson, G. H., Block copolymer thermodynamics - theory and experiment. Annual Review of Physical Chemistry 1990, 41, 525-557. 18. Fredrickson, G. H.; Bates, F. S., Dynamics of block copolymers: theory and experiment. Annual Review of Materials Science 1996, 26, 501-550. 19. Kim, J. K.; Yang, S. Y.; Lee, Y.; Kim, Y., Functional nanomaterials based on block copolymer self-assembly. Progress in Polymer Science 2010, 35 (11), 1325-1349. 20. Ichikawa, T.; Yoshio, M.; Hamasaki, A.; Kagimoto, J.; Ohno, H.; Kato, T., 3D Interconnected ionic nano-channels formed in polymer films: self-Organization and polymerization of thermotropic bicontinuous cubic liquid crystals. Journal of the American Chemical Society 2011, 133 (7), 2163-2169. 21. Nunes, S. P., Recent advances in the controlled formation of pores in membranes. Trends in Polymer Science 1997, 5 (6), 187-192.

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22. Smolders, C. A.; Reuvers, A. J.; Boom, R. M.; Wienk, I. M., Microstructures in phase-inversion membranes .1. formation of macrovoids. Journal of Membrane Science 1992, 73 (2-3), 259-275. 23. Amirilargani, M.; Mohammadi, T., Synthesis and characterization of asymmetric polyethersulfone membranes: effects of concentration and polarity of nonsolvent additives on morphology and performance of the membranes. Polymers for Advanced Technologies 2011, 22 (6), 962-972. 24. Peinemann, K. V.; Abetz, V.; Simon, P. F. W., Asymmetric superstructure formed in a block copolymer via phase separation. Nature Materials 2007, 6 (12), 992-996. 25. Nunes, S. P.; Sougrat, R.; Hooghan, B.; Anjum, D. H.; Behzad, A. R.; Zhao, L.; Pradeep, N.; Pinnau, I.; Vainio, U.; Peinemann, K. V., Ultraporous films with uniform nanochannels by block copolymer micelles assembly. Macromolecules 2010, 43 (19), 8079-8085. 26. Widin, J. M.; Schmitt, A. K.; Schmitt, A. L.; Im, K.; Mahanthappa, M. K., Unexpected Consequences of block polydispersity on the self-Assembly of ABA triblock copolymers. Journal of the American Chemical Society 2012, 134 (8), 3834-3844. 27. Percec, V.; Clough, R. S.; Grigoras, M.; Rinaldi, P. L.; Litman, V. E., Reductive dehalogenation versus substitution in the polyetherification of 4,4'-dihalodiphenyl sulfones with bisphenolates. Macromolecules 1993, 26 (14), 3650-3662. 28. Tang, W.; Kwak, Y.; Braunecker, W.; Tsarevsky, N. V.; Coote, M. L.; Matyjaszewski, K., Understanding Atom transfer radical polymerization: Effect of ligand and initiator structures on the equilibrium constants. Journal of the American Chemical Society 2008, 130 (32), 10702-10713. 29. Xia, J.; Matyjaszewski, K., Controlled/“living” radical polymerization. atom transfer radical polymerization using multidentate amine ligands. Macromolecules 1997, 30 (25), 7697-7700. 30. Lynd, N. A.; Meuler, A. J.; Hillmyer, M. A., Polydispersity and block copolymer self-assembly. Progress in Polymer Science 2008, 33 (9), 875-893.  

 

 

102 

Chapter 3. Use of Nanoparticles and Click Chemistry in the Development of Single-ion Conductors for Lithium Ion Batteries

This chapter describes research aimed at developing single-ion conductors

for lithium ion batteries. The introduction first discusses why single-ion

conductors are important for decreasing concentration polarization and related

voltage losses during battery discharge. Subsequently, I first present work on

nanoparticles coated with immobilized anions as part of single-ion conductors.

This work follows up previous studies by Fadi Asfour and shows that

nanoparticles with grafted polyanions have a higher lithium conterion weight

fraction than nanoparticles coated with only monolayers of anion. However,

because the conductivity of these nanoparticle-PEO electrolytes is not high

enough for battery applications, subsequent work aims toward using click

chemistry to modify PEO directly and create single-ion conductors. These

studies show that the presence of triazole or thioether groups does not limit

conductivity. Thus, click chemistry may provide a useful method for introducing

immobile anions in PEO to create single-ion conductors.

1. Introduction- Ion Conduction in Lithium Ion Batteries

In discharge of a lithium ion battery, electrons flow from the anode to the

cathode through the external circuit, while inside the cell, lithium cations

formed at the anode migrate to the cathode and intercalate into the cathode

material with reduction at the cathode (Figure 3.1). The electrolyte usually

contains a lithium salt dissolved in a solvent, and ideally Li+ ions are the only

current carriers in this region. When anions carry a significant fraction of the

103 

current, concentration polarization occurs, and the battery loses voltage.1

Figure 3.1. Schematic diagram of a lithium ion battery containing a metal

oxide cathode and a graphite anode. The figure also shows redox reaction

during discharge.

Figure 3.2 illustrates the concentration polarization. At the anode, only part

of the Li+ formed by oxidation migrates away to carry current, so Li

+

accumulates. Additionally, anions migrate toward the anode and collect there.

At the cathode, more Li+ is intercalated with reduction than can migrate to the

cathode due to current, so Li+ is depleted. Anions migrate away from the

cathode and are also depleted in this region. These accumulation and

depletion zones decrease the potential drop at the cathode-solution interface

104 

and increase the potential drop at the anode-solution interface to decrease the

battery voltage. If the discharge is slow enough, diffusion will help dissipate the

concentration polarization, but at fast discharge, concentration polarization is a

serious problem. Moreover, the low conductivity in the depleted region near the

cathode increases the ohmic potential drop, which leads to heating and an

additional loss of battery voltage. The effective voltage during discharge is V

(cell voltage) - Vp (polarization voltage), and the voltage needed to charge the

cell is V+Vp. Of course, power output is directly proportional to discharge

voltage.

Figure 3.2. Concentration polarization during discharge of a lithium ion battery. 

The lithium ion transference number (tLi+) is the fraction of current in solution

carried by Li+. For electrolytes with only one cation and one anion, the sum of

the cation and anion transference numbers must equal 1. Typical Li+

transference numbers in PEO-based electrolytes range from 0.2 to 0.4 (Table

3.1), showing that the anion is the dominant current-carrying species. Thus,

concentration polarization during discharge may be severe as more Li+ ions

105 

form at the anode than can migrate away, and more Li+ enters the cathode

than migrates there. Electrolytes with Li+ transference numbers close to 1 are

highly desirable for decreasing concentration polarization.

Lithium Salt Polyether

(or solvent)O/Li ratio

dTemperature

(oC)

tLi+

LiClO4 PEO1000a 20 30 0.23

LiCF3SO3 PEO1000a 24 30 0.21

LiBF4 PEO500b 20 70 0.32

LiPF6 PC/EC/DMCc 1 M 25 0.38±0.04

aPoly(ethyleneoxide) with Mn of 1,000.

bPoly(ethyleneoxide) with Mn of 500.

cPC, propylene carbonate; EC, ethylene carbonate; DMC, dimethyl

carbonate; 1:1:1 is volume ratio.

donly the ether oxygens in PEO are considered.

Table 3.1. Lithium transference numbers for several lithium salts in battery

solvents.1

One way to obtain single-ion (Li+) electrolytes is to attach anions to

polymers through covalent bonds, so the Li+ counterion is the only mobile ion.

As long as all anions are tethered to the polymer and immobile, tLi+ should be

unity.2,3,4 Another method for immobilizing anions involves grafting to

nanoparticles. In this work I began following up on our previous studies with

nanoparticles coated with monolayers of anions. To increase the amount of Li+

106 

per nanoparticles, I grafted polyanions to the particles. Unfortunately, the

conductivity of polyelectrolytes containing these modified particles was

impractically low, so I also began examining methods to introduce anions

directly into PEG.

2. Results and Discussion

2.1. Single-ion Conductors Containing Nanoparticles with Immobilized

Anions.

 

Scheme 3.1. Monolayer modified silica nanoparticle Si-C5NTfLi (silica

nanoparticle derivatized with lithiated N-pentenyl triflouromethane

sulfonamide).5

Scheme 3.1 shows the monolayer-modified nanoparticles (Si-C5NTfLi) that

our group mixes with PEO to create single-ion conductors. Fadi Asfour initially

developed and studied these particles.5 We employ silica nanoparticles with

diameters of around 12, and a 5-carbon spacer separates the trifluoromethane

sulfonamide from the nanoparticle surface.5 To prepare electrolytes, we

disperse the nanoparticles in polyethylene oxide dimethylether (Mw=500 g/mol)

(PEGDME-500). Since the nanoparticles and hence the anions are immobile,

Li+ is the only species that conducts current.

107 

Scheme 3.2. Method for determining the Li+ content of PEO-based

electrolytes.

In following up on previous studies of these conductors, I first determined

the amount of Li in the modified nanoparticles. Quantitative analysis of the

metal content in the TGA residue by using inductively coupled plasma optical

emission spectrometry (ICP-OES) gives an estimate of the number of anions

bound to the nanoparticles. The lithium in the residue should be Li2O or

Li2CO3, and both are water soluble. The TGA residue was stirred in deionized

water for 12 h, and filtered prior to the ICO-OES analysis. The combined

TGA/ICP-OES analysis of the modified particle shows a lithium content of 1.2 x

10-3

g Li/g particles. We prepared electrolytes with various O/Li ratios by

dispersing the Si-C5NTfLi in PEGDME-500, and Table 3.2 presents the O/Li

ratio in the electrolytes.

108 

O/Li ratioa 425 320 230 185

Particle Content (wt%) 18.5 23.6 30.0 35.0

Conductivity at 30 oC (S/cm) 1.3x10

-68.4x10

-71.2x10

-6 5.3x10

-7

aThe O/Li ratio does not include any O from the Si-C5NTfLi particles.

Table 3.2. Particle weight percentages and O/Li for electrolytes prepared from

Si-C5NTfLi dispersed in PEGDME-500.

 

Figure 3.3. Temperature-dependent conductivity of electrolytes containing

different fractions of Si-C5NTfLi dispersed in PEGDE-500. These results were

obtained by Fadi Asfour, and I repeated some of the measurements.5

Figure 3.3 shows the temperature-dependent conductivities of electrolytes

with different particle contents. The conductivities at 30 oC (1000/T=3.3) are

around 10-6

S/cm, and conductivity increases by less than an order of

109 

magnitude on gong from 30 oC (1000/T=3.3) to 80

oC (1000/T=2.83). These

low conductivities may stem from the low lithium content in the electrolyte

materials. As Table 3.2 shows, the O/Li ratio is between 200 and 400 for all the

electrolytes. Increasing the particle content adds Li+ to the electrolyte, but

does not change the conductivity by more than a factor of 3. At high particles

contents, the lack of ionic conductivity through the interior of the nanoparticles

may decrease the overall conductivity. Thus improvements in conductivity will

require increases in the amount of Li per g of particle.

2.2. Single-ion Conductors Prepared Using Nanoparticles Modified by

Grafting of Polyanions

 

Scheme 3.3. Silica nanoparticles prepared by grafting lithiated poly

(trifluoromethane sulfonic aminoethyl-methacrylate) (Si-TfMALi) from the

surface.1

Scheme 3.3 shows our strategy to increase the Li content in modified

silica nanoparticles. Growth of a poly(trifluoromethane sulfonimide aminoethyl-

methacrylate) (TfMALi) from the particles yields many sites for Li+ counterions.

(I describe the synthesis of these particles in my MS thesis.1) TGA-ICP

characterization of the grafted particles shows a lithium content of 2.0 x 10-2

g

Li/g Si-TfMALi particles. Compared to the 1.2 x 10-3

g Li/g Si-C5NTfLi,

110 

Si-TfMALi contains an order of magnitude more Li per g of particles. Mixing

Si-TfMALi particles with PEGDME-500 thus yields high O/Li ratios compared

to those in dispersions of Si-C5NTfLi (compare Tables 3.2 and 3.3).1

O/Li ratioa 16 32 64 96

Particle Content (wt%) 33.2 19.9 11.1 7.7

Conductivity at 30 oC (S/cm) 7.5x10

-73.2x10

-62.1x10

-6 3.1x10

-7

aThe O/Li ratio does not include any O from the Si-TfMALi particles.

Table 3.3. Particle weight percentages and O/Li ratios for electrolytes

prepared from Si-TfMALi dispersed in PEGDME-500.

Figure 3.4. Temperature-dependent conductivity of electrolytes containing

different fractions of Si-TfMALi dispersed in PEGDE-500. The various fractions

of particles (see Table 3.3) lead to the different O/Li ratios shown in the figure.1

111 

Figure 3.4 shows the temperature-dependent conductivities for

dispersions of Si-TfMALi in PEGDME-500 as a function of the O/Li ratios in the

dispersions. The conductivities, which are extracted from impedance

spectroscopy data, are roughly linear with 1/T, consistent with thermally

activated transport. Conductivities at 30 oC are on the order of 10

-6 S/cm,

similar to values with Si-C5NTfLi/PEGDEM-500.

Figure 3.5. Temperature-dependent conductivity for (a) Si-C5NTfLi at O/Li 425

and (b) Si-TfMALi at O/Li 32, both samples contain ~19 wt% modified particles.

Figure 3.5 compares temperature-dependent conductivities for

Si-C5NTfLi/PEGDME-500 (O/Li=425) and Si-TfMALi/PEGDME-500 (O/Li=32)

dispersions. Both composite electrolytes have particle fractions of around 19

wt%, but the polyelectrolyte-modified particles contain much more Li. The

system with a monolayer of anions on the particles (Si-C5NTfLi/PEGDME-500)

112 

exhibits a 2-fold increase in conductivity on going from 30 to 80 °C. At 30 °C

the polyectrolyte system, Si-TfMALi/PEGDME-500, has a conductivity similar

to that of Si-C5NTfLi/PEGDME-500 (a difference of about 0.5 log units), but at

80 °C, the conductivity of Si-TfMALi/PEGDME-500 is a full order of magnitude

higher. Scheme 3.4 presents a proposed explaination for these results.

Li+Li+

Li+Li+

Li+

Li+Li+ Li+

Li+

Li+

Li+ Li+

Li+

Li+Li+Li+

Li+

Li+Li+

N SO

OCF3

1.3 x 10-6 S/cm at 30 oC 2.8 x 10-6 S/cm at 80 oC

3.2 x 10-6 S/cm at 30 oC 2.9 x 10-5 S/cm at 80 oC

Li+Li+

Li+Li+

Li+

Li+Li+ Li+

Li+

Monolayer

Grafted polymer

Li+

Li+

Li+

Li+Li+

Li+

Li+Li+

=

Scheme 3.4. Proposed qualitative conformations of monolayer Si-C5NTfLi

(top) and multilayer Si-TfMALi (bottom) at 30 oC and at 80

oC.

The conformation of the monolayer does not change significantly with

increasing temperature, so the conductivity of Si-C5NTfLi/PEGDME-500

increases marginally on going from 30 to 80 °C. At 80 °C, the polyTfMALi

chains are not highly soluble in PEGDME-500, so only the exterior lithium ions

113 

are accessible to the PEGDME-500 matrix for conductivity. Increasing the

temperature increases the solubility or mobility of the polyelectrolyte in

PEGDME-500, and more Li+ becomes available to the matrix for conductivity.

Thus at 80 oC, the conductivity of Si-TfMALi/PEGDME-500 reaches 3x10

-5

S/cm. The conductivity of this system is an order of magnitude lower than the

values of typical electrolytes used in Li ion batteries,6 but the increase in

conductivity at high temperature suggests that if more Li+ is accessible to

PEGDME-500, we may be able to create competitive single-ion conductors.

2.3. Towards Click Chemistry for Synthesizing Single-ion Conductors

with a High Density of Li+ in PEO

To increase the concentration of Li+ in poly(ethyleneoxide) (PEO) while still

maintaining single-ion conductivity, we aim to eventually graft anionic groups

directly to the PEO backbone (Scheme 3.5). The anionic groups should be

immobile, and most of the Li+ will be available for carrying current. Below I

describe some previous studies of anion insertion via click chemistry and then

present studies aimed at determining whether the triazole or thioether linkers

alter Li+ conductivity.

114 

Scheme 3.5. Proposed single-ion conductors prepared by synthesis of PEO

containing alkene or alkyne groups and subsequent attachment of anions to

these groups via click chemistry.

2.3.1. Prior Use of Click Chemistry for Creating Proton-Conducting

Membranes.

To the best of my knowledge, no studies reported using click chemistry to

prepare Li+ electrolytes. However, several groups employed click chemistry to

synthesize proton-conducting materials. Since proton and Li+ conduction are

similar, in the following section I first review the used of click chemistry

(alkyne-azide7 or thiol-ene

8) for post-functionalization of polymers to create

proton-conductive membranes.

115 

O O SO

ONN

N

O

NaO3S

n

OOSO

ON

NN

O

NaO3S

NN

N

NNN

n

 

Scheme 3.6. Polysulfone structures synthesized by Bielawski’s et al for

proton-conduction.9

Especially relevant to this work, Bielawski et al. synthesized

polysulfone-based polyanions for proton-conductive membranes in methanol

fuel cells.9 Scheme 3.6 shows the structure of these polymers, in which

azide-containing polysulfone was partially functionalized with sulfonate side

chains via alkyne-azide click chemistry; the rest of the azide groups served as

crosslinking points to prepare a gel-like material. The performance of fuel cells

containing click-functionalized polysulfone membranes was comparable to that

116 

with cells containing Nafion-based membranes, with a maximum power output

of 130 mW/cm.2

 

Scheme 3.7. Polyacrylate structures prepared by Martwiset et al. for formation

of membranes that exhibit proton conductivity at 200 oC.

10

Martwiset et al. synthesized polyacrylates containing different numbers of

1H-1,2,3-triazole groups (Scheme 3.7).10

They did not use click chemistry for

post-functionalization of the polymers, but the 1H-1,2,3-triazole groups served

as proton donors (Scheme 3.7) in proton-conducting membrane. In an

anhydrous environment at 200 oC, such membranes exhibited a maximum

conductivity of 17.5 µS/cm, which is comparable to the conductivity of Nafion

under these conditions.

117 

Scheme 3.8. Poly(ether ether ketone) prepared by Gao et al for reaction with

3-mercaptopropyltrimethoxysilane via click chemistry.11

Gao et al. used thiol-ene chemistry to attach the mercaptopropyl

trimethoxysilane to a poly(ether ether ketone) derivative (Scheme 3.8).11

Subsequent crosslinking catalyzed by hydrochloric acid gave a polymer/silica

hybrid material with high dimensional and oxidative stabilities. Although the

proton conductivity of this material is lower than that of the original sulfonated

poly(ether ether ketone), presumably due to cross-linking, the material

maintained relatively high conductivity (10-2

S/cm at room temperature), 5%

and 10% weight loss temperature of the membrane are higher than 280 oC,

these properties made this series of membranes a good alternative for proton

exchange membranes in fuel cell application.

2.3.2. Synthesis of PEO-Containing Click Functionalities

 

Scheme 3.9. The thioether and triazole structures that result from (a) thiol-ene

and (b) alkyne-azido click chemistry, respectively.

The above examples of the use of click chemistry to prepare

118 

proton-conductive polymer electrolyteS suggest that the resulting structures

(either thiol-ethers or 1,2,3-triazoles, Scheme 3.9) are not obstacles to proton

transport. However, I found no previous studies that employed click

chemistry to functionalize polymers for Li+ conduction.

(a)   

 

(b)

Scheme 3.10. (a) Scheme of ideal lithium transport in an electrolyte material

and (b) scheme of lithium transport if the click functionality (triazole or thioether)

impedes Li+ transport.

Scheme 3.10 illustrates a possible challenge of the click structure to Li+

conductivity. The X-axis represents the lithium transport path, and the Y-axis

shows energy barriers for lithium transport. If the click structure has little or no

effect on lithium transport, lithium will encounter no additional barriers to

migration, as shown in Scheme 3.10 (a). The 1,2,3-triazole and sulfide

119 

structures that result from click chemistry, could potentially associate with Li+

to decrease mobility. Click structures, particularly triazole, may make the

polymer back bone more rigid and give a high Tg that could reduce chain

mobility and decrease Li+ conductivity.

12 In these cases, high energy barrier

will appear across the whole lithium transport path, as shown in Scheme 3.10

(b). Finally, the solubility of Li+ in the polymer may decrease because of

unfavorable association with the click functionality.13 Before applying click

chemistry in this field, we decided to examine the influence of the click

structure on Li+ transport in PEO, and this required synthesis of PEO

containing triazoles and thioethers. Dipropargyl and diazido tetraethylene

glycol (Scheme 3.11a) will react to give triazole-containing PEO, and diallyl

and dithiol tetraethylene glycol (Scheme 3.11b) will form sulfur-containing

PEO, so we synthesized these reactants.

 

Scheme 3.11. (a) Monomers synthesized to prepare triazole-containing PEO,

(b) monomers to that will react to give sulfur-containing PEO.

120 

TsCl/KOHr. t.

Scheme 3.12. Two methods for synthesis of dipropargyl tetraethylene glycol.

Reaction of propargyl bromide and tetraethylene glycol successfully gives

dipropargyl tetraethylene glycol in one step (Route 1, Scheme 3.12), but the

propargyl bromide starting material is relatively expensive ($58 for 50 g of an

80 wt% solution in toluene). More importantly this material is potentially

explosive and quite hazardous. To enable large scale synthesis while avoiding

use of the hazardous starting material, we developed Route 2 (Scheme 3.12),

which uses ditosyl tetraethylene glycol as an intermediate and reaction with

propargyl alcohol. We synthesized the target molecule using Route 2 at a

similar yield to Route 1, around 60%.

The tosylate derivative is a very useful and convenient intermediate to

covert hydroxyl groups to other functionalities.14

Conversion of the hydroxyl

group to tosylate using tosyl chloride is quantitative for many substrates, the

reaction condition is mild, and extraction purification usually gives pure product.

In fact, we synthesized three of the four compounds for click reactions using

the tosylate intermediate (Scheme 3.13). The only drawback to this method is

that tosyl chloride is toxic.

121 

Scheme 3.13. Synthesis of several step-growth polymerization monomers via

the ditosyl derivative.

Scheme 3.14. Synthesis of diallyl tetraethylene glycol.

In principle, the method to synthesize dipropargyl tetraethylene glycol in

Scheme 3.13 could be further modified to obtain diallyl tetraethylene glycol.

However, allyl bromide is a relatively cheap commercial material ($35 for 250

mL, Aldrich) and is not hazardous, so we synthesized diallyl tetraethylene

glycol directly from tetraethylene glycol in the one step reaction shown in

Scheme 3.14.

122 

 

Figure 3.6. Kinetics of step-growth polymerization between dipropargyl and

diazido tetraethylene glycol.

 

Scheme 3.15. Step-growth polymerization of diazido and dipropargyl

tetraethylene glycol.

Step-growth polymerization of diazido and dipropargyl tetraethylene

glycol (Scheme 3.15) was conducted using pre-synthesized Cu(PPh3)Br

catalyst. Figure 3.6 shows that after 4 h the reaction conversion plateaus

around 80%. Polymer was isolated by precipitation after adding the reaction

123 

solution into ether, and GPC analysis of the polymer product gave Mw=8.1x104

and PDI=3.0.

 

Scheme 3.16. Step-growth polymerization of dithiol and diallyl tetraethylene

glycol.

Step-growth polymerization of dithio and diallyl tetraethylene glycol was

conducted via a thermally activated process (Scheme 3.16). GPC analysis of

the polymer product gave Mw=7,400 and PDI=1.1.

2.3.3. Comparison of the Conductivity of Li Salts in PEO and PEO with

Click Functionalities.

To determine if the triazole functionality affects the conductivity of Li salts in

PEO, we compared the conductivity of LiClO4 dissolved in a commercially

available polyethylene oxide (PEO, MV=105), with the conductivity of the

polymer obtained from polymerization of diazido and dipropargyl

tetraethylene glycol (Mw=8.1 x 104). Mv is calculated from the viscosity of a

polymer solution. Because polymer chains with higher molecular weights make

solutions much more viscous than chains with smaller molecular weights, Mv >

124 

Mw, which is greater than Mn.

Figure 3.7. Conductivities of mixtures of LiClO4 with pure PEO (black squares)

and triazole-containing PEO (red circles) at different ratios of PEO to LiClO4.

The O/Li ratios in the mixture were determined from the masses of LiClO4 and

PEO added, and these ratios only include the O atoms from PEO.

Measurements occurred at 90 oC.

PEO with this large molecular weight is a solid with crystalline regions.

Previous studies show that the majority of current conduction occurs through

amorphous regions, so we determined conductivity with liquid polymers at 90

oC. The melting point of PEO is around 60 o

C. Figure 3.5 compares the

conductivity of electrolytes prepared with pure PEO and with PEO containing

triazole groups. In the pure PEO material (Mv=105), as the O/Li ratios

decreases from 128 to 64, conductivity increases due to more Li+ and ClO4

-

125 

species in the mixture. The conductivity reaches a peak value of 0.039 S/cm.

Further increases in the LiClO4 concentration (O/Li ratios between 64 and 16)

do not increase conductivity. Previous work shows that at high salt

concentrations ions pair or aggregate, reducing the number and overall

mobility of the ions.15,16

Most importantly, electrolytes made with pure PEO

and PEO containing the triazole structure have similar conductivities. Thus, the

triazole groups that result from alkyne-azido click chemistry do not greatly

impede Li+ transport.

Figure 3.8. Conductivities of mixtures of LiClO4 with pure PEO (black squares)

and thioether-PEO (red circles) at different ratios of PEO to LiClO4. The O/Li

ratios in the mixture were determined from the masses of LiClO4 and PEO

added, and these ratios only include the O atoms from PEO. Measurement

occurred at 90 oC.

126 

Figure 3.8 compares the conductivities of electrolytes made from pure PEO

and PEO containing thioether groups. A commercial poly(ethyleneoxide) (PEO)

with a molecular weight (Mw= 8,000) similar to that of the thioether PEO

served as the control polymer for these experiments. In this case, conductivity

generally increases with increasing concentrations of LiClO4 (decreasing O/Li

ratios). Comparison of Figures 3.7 and 3.8 suggests that the conductivities

are generally a factor of 2 or so higher in the lower molecular weight PEO

(Figure 3.6). The conductivities with pure PEO are about the same as in the

PEO prepared with thiol-ene click chemistry, suggesting that the thioethers do

not impede Li+ transport.

At a specific temperature, ionic conductivity is proportional to the number

of carriers, the charge of the carriers and their mobility. Both cations and

anions contribute to the ionic conductivity data measured by AC impedance

spectroscopy. Thus, the data in Figure 3.7 and 3.8 reflect the mobility of both

lithium cations and perchlorate anions. Previous studies show that with LiClO4

in PEO, 70% - 80% of the conductivity is due to perchlorate anions. It might be

possible that the triazole of thioether species disrupts conductivity from Li+ and

not from ClO4-, but since Li

+ contributes only 20% - 30% of the conductivity, we

do not detect it. However, given that the data show no evidence of a trend in

lower conductivity with triazole or thioethers, any effect would likely be small.

3. Conclusions

The conductivities of single-ion conductors based on nanoparticles with

127 

grafted polyanions and nanoparticles with mono-layers of anions are similar,

despite the larger number of lithium counterions accompanying the polyanions.

This suggests that most of the lithium counterions in the polyanion-grafted

particles do not conduct current, probably due to the low solubility of

polyelectrolyte in PEO. However, electrolytes with polyanion-modified

nanoparticles show relatively large increases in conductivity as temperature

increases, suggesting that more Li+ may be available at high temperature due

to conformational changes.

To create single-ion conductors with higher conductivity, we are

considering grafting anions to PEO using click chemistry. This will avoid

problems with anion solubility in PEO. However, the triazole or thioether

groups in click linkers might impede conductivity. To examine this, we

polymerized tetraethylene oxides using click chemistry and determined the

conductivity of mixtures of LiClO4 with these polymers. Triazole and

thioether-containing PEO were synthesized with one triazole or thioether for

every tetraethylene oxide repeating unit. Conductivities were essentially the

same for LiClO4 mixed with pure PEO and with the new polymers, suggesting

that triazole and thioether groups do not impede Li+ transport.

4. Experimental Section

4.1. Materials

Sodium azide (500 g, Alfa Aesar, 99%), propargyl bromide (125 g, 80 wt%

solution in toluene, Aldrich), potassium carbonate (500 g, ACP Chemicals),

128 

p-toluenesulfonyl chloride (500 g, ACP Chemicals), thiourea (1 kg, Aldrich),

allyl bromide (1 L, reagent grade 97%, Aldrich), poly(ethyleneoxide) (250 g,

Mv=100,000, Aldrich), poly (ethyleneoxide) (500 g, Mn=8,000, Aldrich), sodium

hydride (100 g, 60% dispersion in mineral oil, Aldrich), tetraethylene glycol (1

kg, 99%, Aldrich), lithium perchlorate (100 g, ≥99%, Aldrich) and triethylene

glycol (1 kg, 99%, Aldrich) were used as received. Cu(I)Br (99.999%, Aldrich)

was purified using saturated aqueous NaBr solution. THF was distilled over

sodium metal and benzophenone.

4.2. Characterization

1H and

13C NMR spectra were collected using a Varian UnityPlus-500

spectrometer in CDCl3 with the residual proton signals from the solvent

serving as the chemical shift standard. Conductivity data were collected from

an HP 4192A LF Impedance Analyzer scanning from 5 Hz to 13 MHz with an

applied voltage of 10 mV. The sample cell contains two steel disks that serve

as symmetric electrodes separated by a Teflon collar containing electrolyte

with a radius of 0.61 cm and a thickness of 0.0175 cm. Electrolytes were

equilibrated at a pre-determined temperature for at least 10 minutes before

measurement. The molecular weights of polymers were determined by gel

permeation chromatography (GPC) using two PL-gel 20 m Mixed A columns

and a Waters R401 Differential Refractometer detector at room temperature.

THF served as the eluting solvent at a flow rate of 1 mL/min, and

mono-disperse polystyrene standards were used to calibrate the molecular

129 

weights. The concentration of the polymer solutions used for GPC

measurements was 1 mg/mL. FT-IR spectra were collected in a Mattson

Galaxy 300 spectrometer. FT-IR samples were made by mixing with KBr,

grounded and pressed to pellets. Liquid materials were spread on a KBr pellet

and directly characterized in the instrument.

Quantitative Li analysis was performed using a Varian 710-ES ICP Optical

Emission Spectrometer. Six standard solutions (LiCl concentration of 0, 0.05,

0.5, 1, 2 and 4.5 ppm in 2 wt% HNO3) were used to prepare calibration curves.

Concentrations determined using emission at wavelengths of 460.289 nm,

670.783 nm, 610.365 nm were essentially the same

4.3. Synthesis

Synthesis of Tris (triphenylphosphine) copper(I) bromide Cu(PPh3)3Br: 6

g of triphenylphosphine (23 mmol) was dissolved in 100 mL boiling methanol in

a 250 mL flask. After addition of 1.43 g CuBr2 (10 mmol), the product formed

as a white precipitate, which was collected by filtration and dried under

vacuum at 90 oC overnight. The reaction gave 4.2 g product (62.3% yield )

with a melting point of 169 oC.

17

Synthesis of ditosyl tetraethylene glycol: Tetraethylene glycol (5.1 g, 0.05

mol) was dissolved in 60 mL of THF in a 250 mL round bottom flask. Twenty g

of tosyl chloride (0.105 mol) was added and the mixture was cooled in an ice

bath. In a separate Erlenmeyer flask, 25 g of KOH was dissolved in 30 mL of

deionized water. This KOH solution was transferred to an addition funnel and

130 

slowly added into the 250 mL flask over 20 min. After the addition, the ice bath

was removed, and the reaction was allowed to proceed at room temperature

overnight. Most of THF was removed by rotary evaporation, and the product

was extracted from the residual solution with dichloromethane (3 x 100 mL).

The organic layer was washed with deionized water (4 x 200 mL) and dried

over MgSO4. The solvent was removed by rotary evaporation, and the product

was dried under vacuum to give 23.8 g of product as a viscous liquid (94%

yield). See Appendix 1 for the 1H NMR spectrum.

Synthesis of diazido tetraethylene glycol: Ditosyl tetraethylene glycol

(10.04 g, 0.02 mol), sodium azide (3.9 g, 0.06 mol) and 150 mL DMF were

mixed in a 500 mL flask at 90 oC overnight. After vacuum distillation to remove

DMF, the residual mixture was dissolved in 70 mL deionized water and the

product was extracted into dichloromethane (3 x 100 mL). The organic layer

was washed three times with 200 mL of deionized water and dried over

MgSO4. After rotary evaporation of solvent, the product was purified by silica

column chromatography (hexane/EtOAc=1:1), to give 3 g of product as a light

orange oil (61.5% yield). See Appendix 4 for the 1H NMR spectrum.

Synthesis of dipropargyl tetraethylene glycol:

Route 1 (using tetraethylene glycol and propargyl bromide): In a 250 mL

3-neck flask under N2, 5.68 g tetraethylene glycol (28.4 mmol) was dissolved

in 60 mL dry THF prior to gradual addition of 5.68 g sodium hydride (0.142 mol)

while stirring. After 20 minutes, the 3-neck flask was placed in an ice bath, and

131 

a solution containing 12.52 g of propargyl bromide (91 mmol) and 0.022 g

18-crown-6 (0.08 mmol) in 30 mL dry THF was slowly added to the flask

through an addition funnel over 10 minutes. The ice bath was then removed,

and the reaction was allowed to proceed at room temperature overnight.

Subsequently, 30 mL of deionized water was added, and the mixture was

stirred for 40 minutes to quench the reaction. Most of the THF was removed

by rotary evaporation, and the product was extracted from the residual solution

with dichloromethane (3 x 150 mL). The combined organic layer was dried

over MgSO4 and column chromatography (silica, hexane/ethyl acetate 1/4)

gave 3.3 g pure product (12.8 mmol, 45.2% yield).

Route 2 (using ditosyl tetraethylene glycol and propargyl alcohol): In a

300 mL beaker 7.5 g NaH in mineral oil (0.1875 mol) was added to 150 mL

pentane and stirred with a magnetic bar for 10 min. The NaH in the suspension

was allowed to settle, and a 50 mL syringe was used to carefully remove the

supernatant. The above process was repeated to give purified NaH. Next, 10.5

g propargyl alcohol (0.1875 mol) was dissolved in 200 mL dry THF in a 500 mL

round bottom flask, and 7.5 g of NaH was slowly transferred into this flask

under N2. After 30 min of stirring at room temperature, 20 g ditosyl

tetraethylene glycol was added, and the flask was heated at 60 oC overnight.

Fifty mL of deionized water was added to the flask, and after 10 min, most of

the THF was removed by rotary evaporation. The product was extracted in

dichloromethane (3 x 100 mL) and washed with deionized water (4 x 200 mL)

132 

before drying over MgSO4. The solvent was removed by rotary evaporation,

and the product was purified by silica column chromatography

(hexane/EtOAc=1:1) to give 7 g of product (65% yield) as a light yellow oil. See

Appendix 7 for the 1H NMR spectrum.

Alkyn-azido Step growth polymerization: 1.318 g of diazido tetraethyleen

glycol (5.4 mmol), 1.458 g of diacetylene tetraethylene glycol (5.4 mmol) and

0.05 g Cu(PPh3)3Br (0.01 equiv.) were dissolved in 20 mL of chloroform in a

100 mL Schlenk flask and allowed to react at 60 oC for 24 h, After cooling to

room temperature, this solution was added dropwise to 200 mL diethyl ether

with strong stirring. Product was precipitated as a light brown viscous oil, which

was dissolved in chloroform and precipitated in ether again. The product was

dried under vacuum (1.2 g, 43% yield). GPC (THF solvent, PS standard)

showed Mn=2.73 x 104, Mw=8.11 x 10

4, PDI=3.0. See Appendix 15 for the

1H

NMR spectrum.

Synthesis of dithiol tetraethylene glycol: In a 250 mL round bottom flask,

20.1 g ditosyl tetraethylene glycol (0.04 mol), 40 mL of ethanol, and 6.1 g of

thiourea (0.08 mol) were added to 30 mL of deionized water. The solution was

purged with nitrogen for 15 minutes, and the flask was fitted with a condenser.

After reflux for 15 h, a solution of 4 g NaOH (0.1 mol) in 40 mL deionized water

was added, and after another 2 h of reflux, the flask was placed in an ice bath.

Fifteen mL of concentrated HCl solution was added to neutralize the solution,

and the product was then extracted in dichloromethane (3 x 50 mL). The

133 

combined dichloromethane solution was dried over MgSO4, solvent was

removed by rotary evaporation, and vacuum distillation gave 4 g of dithiol

tetraethylene glycol (0.025 mol, 62%) as colorless oil. See Appendix 12 for the

1H NMR spectrum.

Synthesis of diallyl tetraethylene glycol: In a 500 mL round bottom flask,

11.6 g of dihydroxyl tetraethylene glycol (0.06 mol) and 14 g of powderized

KOH (0.25 mol) were dissolve in 200 mL of acetone. After placing the flask in

an ice bath, 10 mL of allyl bromide (0.12 mol) was slowly added over 10

minutes. The ice bath was then removed, and the mixture was allowed to react

at room temperature overnight. Acetone was removed using rotary

evaporation, and the product was dissolved in 300 mL dichloromethane.

Deionized water was used to wash the dichloromethane solution (3 x 80 mL),

the organic layer was dried using MgSO4, and solvent was removed by rotary

evaporation. Silica column chromatography (hexane/ethyl acetate 9/1) gave

10.84 g (0.042 mol, 70% yield) of product. See Appendix 10 for the 1H NMR

spectrum.

Thiol-ene Step growth polymerization: 6.46 g diallyl tetraethylene glycol

(0.024 mol), 5.36 g dithiol tetraethylene glycol (0.024 mol) were dissolved with

100 mL dichloromethane in a 250 mL round bottom flask. The solution was

purged with nitrogen for 30 minutes and was done in a 50 oC oil bath for 24 h.

To work up the reaction, the mixture was put under rotovac to remove residual

solvent. The product was dissolved in 100 mL chloroform and added dropwise

134 

to 200 mL diethyl ether with strong stirring. Product was obtained as a light

yellow viscous oil, which was dissolved in chloroform and precipitated in ether

again. Polymer product was dried under vacuum as viscous oil (11.5 g, 97.3%).

GPC: Mn=6,700, Mw=7,400, PDI=1.1. See Appendix 14 for the 1H NMR

spectrum.

 

 

 

 

 

 

135 

 

 

 

 

 

 

 

 

 

APPENDIX B  

 

136 

Appendix B1. 1H NMR spectrum of ditosyl tetraethyleneglycol in CDCl3.

137 

 

Appendix B2. 13

C NMR spectrum of ditosyl tetraethyleneglycol in CDCl3.

138 

Appendix B3. FT-IR spectrum of ditosyl tetraethyleneglycol.

139 

 

Appendix B4. 1H NMR spectrum of diazido tetraethyleneglycol in CDCl3.

140 

 

Appendix B5. 13

C NMR spectrum of diazido tetraethyleneglycol in CDCl3.

141 

 

Appendix B6. FT-IR spectrum of diazido tetraethyleneglycol.

142 

 

Appendix B7. 1H NMR spectrum of dipropargyl tetraethyleneglycol in CDCl3.

143 

 

Appendix B8. 13

C NMR spectrum of dipropargyl tetraethyleneglycol in CDCl3.

144 

 

Appendix B9. FT-IR spectrum of dipropargyl tetraethyleneglycol.

145 

 

Appendix B10. 1H NMR spectrum of diallyl tetraethyleneglycol in CDCl3.

146 

 

Appendix B11. FT-IR spectrum of diallyl tetraethyleneglycol.

147 

 

Appendix B12. 1H NMR spectrum of dithiol tetraethyleneglycol in CDCl3.

148 

 

Appendix B13. 13

C NMR spectrum of dithiol tetraethyleneglycol in CDCl3.

149 

Appendix B14. 1H NMR spectrum of dithiol tetraethyleneglycol in CDCl3.

150 

 

Appendix B15. FT-IR spectrum of dithiol tetraethyleneglycol.

151 

Appendix B16. FT-IR spectrum of thioether-PEO.

152 

 

Appendix B17. 1H NMR spectrum of triazole-PEO in CDCl3.

153 

 

Appendix B18. FT-IR spectrum of triazole-PEO.

154 

 

 

 

 

 

 

 

 

 

 

 

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