dendrimers and dendronized polymers - synthesis and - diva

Dendrimers and Dendronized Polymers - Synthesis and Characterization

Andreas Nyström

Doctoral Thesis

Stockholm 2006

Som med tillstånd av Kungliga Tekniska Högskolan i Stockholm framlägges till offentlig granskning för avläggande av teknisk doktorsexamen fredagen den 2 juni 2006, kl 10.00 i sal D2, Lindstedsvägen 5, KTH, Stockholm. Avhandlingen försvaras på engelska.

Contact information: Address: KTH Department of Fiber and Polymer Technology

Coating Technology Royal Institute of Technology Teknikringen 56-58 SE 100 44 Stockholm Sweden

Copyright © Andreas Nyström All rights reserved Paper I © 2004 American Chemical Society. Paper II © 2005 Wiley Periodicals, Inc. Paper III © 2005 Wiley Periodicals, Inc. Printed by Universitetsservice US AB Stockholm, Sweden, 2006 TRITA-FTP-Report 2006:10 ISSN 1652-2443 ISRN KTH/FPT/R-2006/10-SE ISBN 91-7178-333-4

Abstract The goal of this work was to synthesize complex macromolecular architectures such as

dendrimers and dendronized polymers, and evaluate the effect from the dendrons on the material properties of the polymers. The work presented in this doctoral thesis, Dendrimers and Dendronized Polymers - Synthesis and Characterization, is divided into one minor and one major part. The first part deals with the synthesis and characterization of two sets of dendritic porphyrins based on 2,2-bis(methylol)propionic acid (bis-MPA). The second part deals with the synthesis and characterization of dendronized poly(hydroxyl ethyl methacylate), dendronized poly(norbornene), and dendronized triblock copolymers, where the pendant dendrons are based on bis-MPA.

Both free-base and zinc containing dendritic porphyrins were synthesized up to the fifth generation by employing iterative ester coupling utilizing the acetonide protected anhydride of bis-MPA as generic building block.

First and second generation dendron bearing methacrylates based on 2-hydroxyethyl methacrylate were also synthesized by utilizing the acetonide protected anhydride of bis-MPA, and subsequently polymerized by atom transfer radical polymerization. By adopting a divergent “graft-to” approach starting from the first generation dendronized poly(hydroxyl ethyl methacrylate), well-defined dendronized polymers with acetonide, hydroxyl, acetate and hexadecyl surface functionality were obtained.

By utilizing the same divergent iterative esterification, first to fourth generation dendron functionalized norbornenes were synthesized. The monomers were polymerized by ring-opening metathesis polymerization, utilizing either Grubbs´ first or second generation catalyst.

Acrylate functional first to fourth generation monomers were synthesized by the copper(I) catalyzed “click” coupling of azido functional dendrons and propargyl acrylate. The monomers were polymerized to dendronized triblock copolymers by reversible addition-fragmentation chain transfer polymerization, utilizing a difunctional macro chain transfer agent based on poly(methyl methacrylate).

The bulk properties of the dendronized poly(hydroxyl ethyl methacrylate) and poly(norbornene) were investigated by dynamic rheological measurements and differential scanning calorimetry. It was found that all the acetonide functional dendronized polymers had glass transitions temperatures in a similar range. The rheological behaviour showed that for the dendronized polymers having the same backbone length (poly-HEMA) the complex viscosity as a function of functionality was independent of the surface functionality of the polymer. The generation number of the polymer had a profound influence on the complex viscosity, changing form a Newtonian behaviour to a shear thinning behaviour when the generation of the dendrons was increased from two to four. The dendronized poly(norbornene) had increasingly shorter backbone lengths for each generational increase, and for the materials set with comparably lower degree of polymerization, the G’ part of the complex modulus was mostly affected by attaching larger dendrons. In the case of the sample set of higher degree of polymerization, the second, third, and fourth generation samples had similar slopes of the G’ and G” curves, indicating a similar relaxation behaviour.

Keywords: Dendrimers, dendronized polymers, atom transfer radical polymerisation, ring-opening metathesis polymerization, reversible addition-fragmentation chain transfer polymerization, 2,2-bis(methylol)propionic acid, tri-block copolymers, rheology, differential scanning calorimerty, 1H-NMR self-diffusion.

Sammanfattning Syftet med detta arbete har varit att syntetisera komplexa makromolekylära arkitekturer,

såsom dendrimerer och dendroniserade polymerer, samt att undersöka effekten av dendroner på materialens mekaniska egenskaper. Arbetet som presenteras i denna doktorsavhandling, Dendrimerer och Dendroniserade Polymerer – Syntes och Karakterisering, är uppdelat i två delar. Den första mindre delen, behandlar syntes och karakterisering av två uppsättningar av dendritiska porfyriner, där de dendritiska segmenten baseras på 2,2-bis(metylol)propionsyra (bis-MPA). Den andra större delen av denna avhandling behandlar syntes och karakterisering av dendroniserade poly(hydroxyl etyl metakrylater), dendroniserade poly(norbornener) samt dendroniserade triblock sampolymerer, där de pendanta dendronerna i dessa strukturer är uppbyggda av bis-MPA.

Både fri bas- och zink innehållande dendritiska porfyriner upp till den femte generationen framställdes genom en divergent iterativ esterifiering med hjälp av den acetonidskyddade anhydriden av bis-MPA som generisk byggsten.

Första och andra generationens dendron funktionaliserade metakrylater baserade på 2-hydroxyletyl metakrylat (HEMA) framställdes på ett liknande divergent vis med hjälp av den acetonidskyddade anhydriden av bis-MPA. Dessa monomerer polymeriserades sedan med hjälp av atom transfer radical polymerization. Genom att använda en divergent ”graft-to” metod kunde väldefinierade dendroniserade polymerer med acetonid-, hydroxyl-, acetat- och hexadekylfunktionalitet framställas.

Med samma divergenta iterativa esterifieringsmetod framställdes även den första till fjärde generationens dendronbärande norbornener. Dessa monomerer polymeriserades genom ring-opening metathesis polymerization, katalyserad av första eller andra generationens Grubbs katalysatorer.

Akrylatfunktionella första till fjärde genrationens monomerer syntetiserades genom koppar(I) katalyserad “click” koppling mellan en azid funktionell dendron och propargyl akrylat. Monomererna polymeriserades till dendroniserade triblocksampolymerer genom reversible addition-fragmentation chain transfer polymerization, där en difunktionell poly(metylmetakrylat) användes som makrokedjeöverföringsagent.

Materialegenskaperna hos de dendroniserade poly(hydroxyl etyl metakrylaterna) och de dendroniserade poly(norbornenerna) undersöktes med hjälp av dynamiska reologiska mätningar och differential scanning calorimetry (DSC). DSC mätningarna visade att alla acetonidfunktionella dendroniserade polymer uppvisade glastransitionstemperaturer inom samma område. De reologiska mätningarna visade att de dendroniserade polymererna med samma huvudkedjelängd (baserade på HEMA), oberoende av funktionalitet, hade samma komplexa viskositetsbeteende. Däremot visade det sig att generationstalet hos dessa polymerer hade en stark inverkan på den komplexa viskositeten, som ändrades från ett newtonskt till ett skjuvförtunnande beteende när generationen hos dendronen ökades från två till fyra. De dendroniserade poly(norbornenerna) hade minskande huvudkedjelängd med ökande generation. För materialserien med jämförbart kortare huvudkedja visade det sig att G’ delen av den komplexa modulen påverkades mest av ökande dendrongeneration. För materialserien med längre huvudkedja visade sig den andra, tredje och fjärde generationens material ha liknande lutning på G’ och G” kurvorna, viket indikerar att de har ett liknande relaxationsbeteende.

List of papers This thesis is a summary based on the following papers; I. “Porphyrin Cored Bis-MPA Dendrimers”, R. Vestberg, A. Nyström, M. Lindgren, E. Malmström, A. Hult, Chemistry of Materials, 2004, 16, 2794-2804. II. ”Dendronized Polymers with Tailored Surface Groups”, A. Nyström, A. Hult, Journal of Polymer Science Part A: Polymer Chemistry, 2005, 43, 3852-3867. III. “Bulk Properties of Dendronized Polymers with Tailored End-groups emanating from the same Backbone”, A. Nyström, I. Furó, A. Hult, Journal of Polymer Science Part A: Polymer Chemistry, 2005, 43, 4495-4503. IV. “Characterization of Poly(norbornene) Dendronized Polymers Prepared by Ring-Opening Metathesis Polymerization of Dendron Bearing Monomers”, A. Nyström, M. Malkoch, I. Furó, D. Nyström, K. Unal, P. Antoni, G. Vamvounis, C. Hawker, K. Wooley, E. Malmström, A. Hult, Manuscript, 2006. V. “Dendronized ABA Triblock copolymers by Reversible Addition-Fragmentation Transfer Polymerization”, A. Nyström, M. Malkoch, E. Malmström, A. Hult, Submitted to Macromolecules, 2006. VI. “Solution Properties of Dendronized Poly(Hydroxy Ethyl Methacrylate) Polymers” S. Hietala, A. Nyström, H. Tenhu, A. Hult, Accepted for publication in Journal of Polymer Science Part A: Polymer Chemistry, 2006. My contribution to the appended papers: Paper I. Synthesized 50 % of the materials presented in the paper and wrote half of the experimental part. Paper II. Performed all the experimental work except the SEC characterization and wrote the paper. Paper III. Performed all the experimental work except the diffusion NMR measurements and wrote all parts of the paper except the section on diffusion NMR. Paper IV. Performed 90 % of the experimental work and wrote all parts of the paper except the sections on AFM, and porous membranes. Paper V. Performed all the experimental work except the SEC characterization and wrote the paper. Paper VI. Synthesized the materials used in the study, performed the dn/dc and SEC characterization.

1 Purpose of the Study .............................................................................................. 1

2 Introduction............................................................................................................ 2

2.1 General background ..................................................................................... 2

2.2 Dendrimers .................................................................................................... 2

2.3 Porphyrins ..................................................................................................... 3

2.4 Controlled polymerization techniques........................................................ 4 2.4.1 Atom Transfer Radical Polymerization (ATRP) ........................................ 4 2.4.2 Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT).................................................................................................................... 6 2.4.3 Ring-Opening Metathesis Polymerization (ROMP)................................... 7

2.5 Dendronized Polymers ................................................................................. 8 2.5.1 Synthesis of Dendronized Polymers ........................................................... 8

3 Experimental ........................................................................................................ 10

3.1 Instrumentation .......................................................................................... 10

3.2 Materials ...................................................................................................... 12

4 Results and Discussion ........................................................................................ 13

4.1 Synthesis of Dendritic Porphyrins (Paper I) ............................................ 13 4.1.1 Porphyrin Synthesis .................................................................................. 13 4.1.2 Characterization of the Dendritic Porphyrins ........................................... 15

4.2 Dendronized Poly(hydroxyl ethyl methacrylate) (Paper II)................... 18 4.2.1 Synthesis of the macromonomers ............................................................. 18 4.2.2 Polymerization of the macromonomers via ATRP................................... 18 4.2.3 Characterization by Size Exclusion Chromatography.............................. 21

4.3 Dendronized Poly(hydroxyl ethyl methacrylate) via the ‘Graft-onto’ Route (Paper II) ...................................................................................................... 23

4.3.1 Acetonide, Acetate and Hydroxyl Functional Dendronized Polymers..... 23 4.3.2 Aliphatic Hexadecyl Functional Dendronized Polymers ......................... 24 4.3.3 Characterization by Size Exclusion Chromatography.............................. 25

4.4 Dendronized Poly(norbornene) (Paper IV).............................................. 26 4.4.1 Synthesis of the dendron bearing monomers............................................ 26 4.4.2 Polymerization of the norbornenyl macromonomers ............................... 26

4.5 Dendronized Triblock Copolymers (Paper V) ......................................... 29 4.5.1 Synthesis of the dendron bearing acrylates............................................... 29

4.5.2 Polymerization of the acrylate functional macromonomers..................... 30

4.6 Bulk Properties of the Dendronized Polymers (Papers III, and IV)...... 33 4.6.1 Differential Scanning Calorimery – Dendronized Poly(hydroxyl ethyl methacrylate)......................................................................................................... 33 4.6.2 Differential Scanning Calorimery – Dendronized Poly(norbornene)....... 35 4.6.3 Rheological Characterization - Dendronized Poly(hydroxyl ethyl methacrylate)......................................................................................................... 36 4.6.4 Rheological Characterization - Dendronized Poly(norbornene) .............. 38

1H-NMR Diffusion and Relaxation studies (Papers III and VI)......................... 41 4.6.5 Dendronized Poly(hydroxyl ethyl methacrylate)...................................... 41

4.7 Birefringent Fibers Dendronized Poly(norbornene) (Paper IV)............ 43

5 Conclusions .......................................................................................................... 45

6 Future Work......................................................................................................... 46

7 Acknowledgements............................................................................................... 47

8 References ............................................................................................................ 49

9 Appendix I. Structures of the synthesized monomers and polymers ................. 54

Purpose of the Study

1 Purpose of the Study There is a rapidly growing need for organic materials with tailored properties. Under the

last decade various hyperbranched polymers have been commercialized and are now being used in a number of high performance applications. Dendrimers and dendronized polymers represent polymeric materials with complex macromolecular architectures where the material properties can be tailored for specific advanced applications. In order to tailor these materials for future applications such as degradable drug carriers and optical power limiting materials, new and versatile synthetic tools must be developed. Further, the structure-property relationship of these materials must be further understood.

The main goal of this work is to develop versatile tools for the synthesis of dendrimers and dendronized polymers, and with these materials at hand evaluate the effect of architecture and functionality on the material properties.

To achieve these macromolecular architectures, dendrimer chemistry has been combined with both atom transfer radical polymerization, ring-opening metathesis polymerization, and reversible addition-fragmentation chain transfer polymerization.

This work is divided into two parts, the first minor parts deals with the synthesis and characterization of a set of dendritic porphyrins. The second major part of this work is devoted to the synthesis and characterization of three sets of different dendronized polymers. The dendritic porphyrins and the dendronized polymers are aliphatic polymers based on 2,2-bis(methylol)propionic acid (bis-MPA) which can serve as a scaffold for a variety of functionalities.

1

Introduction

2

2 Introduction

2.1 General background By the development of synthetic macromolecules with more complex architectures,

polymers with new properties can be attained. Elucidating the structure-property relationship of such materials is important in order to meet the demands for well characterized materials in emerging research areas such as nanotechnology and medicine. This chapter aims to give a brief introduction to the areas of dendrimers, dendronized polymers, and controlled polymerization techniques.

2.2 Dendrimers Since the discovery of dendrimers in the late 70´s,1-3 the research interest for developing

new synthetic routes as well as finding new applications for dendrimers are ever increasing.4-9 In contrast to ordinary synthetic polymers, dendrimers are virtually monodisperse highly branched molecules.8 A dendrimer is built up of layers of ABx repeating units around a central core. Each layer of ABx monomers builds up one generation. One wedge of a dendrimer is called a dendron. Because of the branching of the repeating unit, the numbers of end-groups increase with each generation, resulting in a large number of terminal units at high generations. Figure 1 displays a schematic representation of a bis-MPA dendron and dendrimer.

Figure 1. General representation of a dendron and dendrimer.

There are two main synthetic routes for dendrimers, the convergent (A) and the divergent route (B).8 In the convergent route, the synthesis start at the end-groups and grow towards the core. Each step involves the coupling of the focal point of the dendron to the ABx monomer and finally to the core molecule, forming the dendrimer in the last step.10 In the divergent

Introduction

3

route, the chemistry starts off at the core, and the generations are added sequentially to the end-groups of the dendrimer.3 Figure 2 displays an example of the divergent and convergent routes.

Figure 2. Convergent route (A), divergent route (B).

At higher generations the dendrimers will adopt a more globular structure due to their

branched structure.11 The highly branched structure in combination with the large number of end-groups give rise to a number of unique dendritic properties for example, high solubility,12,13 unusual rheological behavior,14 and site isolation phenomena.8,15,16 Because of the highly branched structure of the dendrimer, properties such as solubility, glass transition temperature, and size can be altered by varying the generation number, the type of repeating unit, and the functionality of the end-groups. Because of the high number of end-groups, most dendritic properties are strongly end-group dependent and by end-group tailoring, properties such as hydrophilicity/hydrophobicity can be introduced.

2.3 Porphyrins Porphyrins are strongly colored conjugated cyclic compounds that are abundant in

nature.17 Metal complexes of porphyrins act as active sites in a number of enzymes, and porphyrins bear structural similarities to the heme group in hemoglobin and chlorophyll.17 A number of applications for synthetic porphyrins have been studied for example, as light emitting diodes (LED),18,19 and as photosensitizes for photodynamic therapy.20,21 Figure 3 shows a commonly studied porphyrin, tetraphenylporphyrin (TPP) in its free base state. The core of the porphyrin ring can be used to complex a number of metal ions by exchanging the hydrogens in the center. If large ions are inserted into the core, the otherwise planar porphyrin ring will change its conformation. The spectral properties of porphyrins can be altered to a wide extent by changing the substitution of the porphyrin ring as well as by the choice of metal-ion complex. Dendron functionalized metal containing porphyrins have also been used to synthesize dendronized polymers. Zimmermann et. al.22 used metal containing porphyrins

Introduction

4

that were stacked and bridged by succinate ligands. The pendant dendrons carried functional groups that could be further used to covalently crosslink the surface of the dendronized polymer by ring-opening methathesis polymerization.

Figure 3. Tetraphenylporphyrin (TPP).

Since dendrimers can offer increased solubility and allow for site isolation around a core

moiety, a large number of studies have been devoted to synthesizing porphyrins with dendritic units. Examples include bis-MPA dendrimers,11,15 benzyl ether type dendrimers,11,15,23-25 and glutamic dendrimers.26,27

2.4 Controlled polymerization techniques True living/controlled polymerizations occur without termination or transfer reactions and

proceed to full conversions with very low polydispersity (PDI). There are a number of controlled polymerization techniques such as living anionic-, cationic-, group-transfer and ring-opening polymerization. They all suffer from the drawback of being sensitive to impurities such as oxygen and water, as well as being demanding in craftsmanship. Therefore, a number of controlled radical polymerization techniques have been developed. They combine synthetic versatility with good control over molecular weight and PDI. Atom transfer radical polymerization (ATRP),28-31 nitroxide mediated free radical polymerization (NMP),32-

34 and reversible addition-fragmentation chain transfer (RAFT)35-38 are examples of CRP techniques. They are all based on the same principle of keeping the propagating radical concentration low in order to suppress unwanted side-reactions. This is achieved by creating a dynamic equilibrium between active (radical) and dormant species that is strongly shifted towards the dormant species.

2.4.1 Atom Transfer Radical Polymerization (ATRP) One of the controlled radical polymerization techniques is Atom Transfer Radical

Polymerization (ATRP).31 ATRP offers the possibility to polymerize a range of vinyl monomers such as acrylates, methacrylates, and styrenes among others, with good control over molecular weight and PDI.31

The typical initiators used in ATRP are alkyl halides (bromine, iodine or chlorine). Figure 4 (top) depicts two commonly used initiators. These halides allow for fast and selective migration between the propagating chain and the transition metal complex. This is necessary in order to obtain well defined polymer with low PDI. If the initiation reaction is fast and side-reactions and termination are negligible, the number of growing chains will be constant and equal to the initial initiator concentration.31

Introduction

5

A great variety of ligands have been employed in ATRP, and they are mostly nitrogen based31,39 but phosphorus and iron based ligands have also been used.31 Figure 4 (bottom) depicts two common nitrogen based ligands. The ligand plays several important roles in the ATRP process. Firstly, the ligand determines the position of the dynamic equilibrium of the ATRP process and thereby also the rate of polymerization and as a consequence the PDI. Secondly, the ligand facilitates the solution of the transition metal in the reaction mixture.31

O

O

BrO

O

Br

N N

N Figure 4. Common initators (top), and ligands (bottom) for ATRP.

The most commonly used transition metals are copper based because of their synthetic versatility and low cost.31

A schematic representation of the mechanism of ATRP is displayed in Figure 5.31 The active species is formed by the homolytical cleavage of the alkyl-halide bond of the initiator. This reversible redox reaction is catalyzed by a metal complex and forms a carbon centered radical on the alkyl while the abstracted halogen oxidizes the transition metal. The radical will then either propagate or shift to the dormant species. The equilibrium of the activation/deactivation must be shifted towards the dormant species otherwise the polymerization will proceed in an uncontrolled fashion.

R-X Cu[I]X/Ligand R X-Cu[II]X/Ligand

monomer P1

Pn-X

Keq

Pn

Pn Pn+1

Rkp

kp

Pn+m

X=Cl, Br

Cu[I]X/LigandKeq

X-Cu[II]X/Ligand

monomer

Pn Pm

+

+

+

+

+

+

+

kt

Initiation

Propagation

Termination

Figure 5. The mechanism of ATRP.

Introduction

6

2.4.2 Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT)

Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT) is one of the most versatile controlled radical polymerization techniques, but suffers from the drawback that the chain transfer agents employed often are tedious to synthesize.38 RAFT have been utilized to polymerize monomers such as; styrenics, acrylates, methacrylates, acrylamides, methacrylamides, and vinylacetates among other monomers.38 Advanced polymeric architectures such as block, stars, and dendronized polymers have also been prepared by RAFT.38

The RAFT process is based on the concept of introducing a small amount of dithioester chain transfer agent in conventional free radical system (monomer + initiator).38 Common chain transfer agents are dithioesters, xanthates, trithiocarbonates, dithiocarbamates, and general examples of these structures are given in Figure 6.38 The reactivity of these chain transfer agents is greatly affected by the nature of the R and Z group.38

S

SR

S

O SRR'

S

S SRR'

S

N SRR'

"R

Dithioester Xanthate Trithiocarbonate Dithiocarbamate

S

Z SR

General structure

Figure 6. Common chain transfer agents.

The mechanism of the RAFT process is depicted in Figure 7, and can be described as follows.38 The radical species formed from the decomposition of the initiator reacts with the monomer (step 1 Figure 7). The growing polymer chain Pn

• adds to the reactive C=S bond of the chain transfer agent (step 2). The intermediate can reversibly release either the reinitiating group R•, or the initial growing chain Pn

•. The R group can then reinitiate the polymerization by reacting with the monomer, forming Pm

• (step 3) or react back with the chain transfer agent (step 2). When the initial chain transfer agent has been consumed the macro chain transfer agent is the only species present, and the polymerization is considered to be in its main equilibrium (step 4). The fast exchange active and dormant chains controls the polymerization and hence the PDI.

Introduction

7

Ini2 Ini*1/2 Monomer Pn*1) +

Z

S

S R Z

S

S R

Pn

Z

S

S

Pn

Pn*2) +*

+ R*

3) R* Monomer Pm*+

Z

S

S

Pn

Z

S

S

Pn

Pm Z

S

S Pm

4) Pm*

Monomer

+

*

Pn*

Monomer

+

5) Pn*Pm* +

P1

β

ktc Pn+m

Pn=

ktd

ki

kadd

k-add

k

βk-

kre-in kp

PmH

Figure 7. The mechanism of RAFT.

The Z group strongly affects the stability of the thiocarbonyl–thioradical intermediate,

strong stabilizing groups favors the formation of the intermediate resulting in higher activity towards radical addition.38 Z groups that form very stable intermediates are unfavorable since they disfavor fragmentation (release of the reinitiating species R•).38 In general, benzyl Z groups offers the best balance between intermediate formation and release of R• group for most common monomers.38 The R group should be a better leaving group compared to the growing polymer chain and be a good reinitiating species towards the monomer used (step 3 in Figure 7).38

2.4.3 Ring-Opening Metathesis Polymerization (ROMP) Ring-opening Methathesis Polymerization (ROMP) is a versatile tool for the synthesis of

well defined polymers from various strained monomers such as norbornenes and cyclobutenes.40-42 In the ROMP polymerization, cyclic olefins are converted to unsaturated polyalkenes, with the driving force for the polymerization being the release of ring-strain.42 Block copolymers, comb polymers, Janus-type polymers, liquid crystalline polymers and dendronized polymers are examples of advanced macromolecular architectures synthesized via ROMP.40,41 The mechanism of ROMP are presented in Figure 8, and involves the reversible cycloaddition of a metal-carbene or metal-alkylidene to a C=C double bond. This step is then followed by a cycloreversion and an additional insertion of a strained monomer.40,41

Mn

M CHRM

R MR

R

Figure 8. Mechanism for the Ring-Opening Metathesis Polymerization (ROMP).

Introduction

8

Catalysts used in ROMP are usually based on titanium, tungsten, molybdenum, or ruthenium.41 Of these transition metals, ruthenium is among the most commonly used metals for catalysts for olefin methathesis reactions since they have the highest functional group tolerance, and the lowest sensitivity towards moisture and oxygen.42,43 Figure 9 depicts two of the commercially available ruthenium catalysts developed by Grubbs et al.42

RuCl

Cl

PCy3

PCy3Ph

NN

RuCl

Cl PCy3Ph

Figure 9. Grubbs´ first generation catalyst (left), second generation catalyst (right).

2.5 Dendronized Polymers Dendronized polymers are formally a sub-group of comb polymers, where the linear

chains of the grafts have been replaced by dendrons as depicted in Figure 10.44-46 The properties of these kinds of polymers are believed to depend on a number of factors, such as type of dendron, attachment density along the backbone, end-group functionality, and degree of polymerization.47,48 Because of the large number of properties that can be tailored independently in this type of architecture, several novel applications have been proposed, for example building blocks for nanometer sized construction,49,50 efficient light emitting materials,51 isolating conducting polymers,52 complexation agents for DNA,53 degradable drug carriers,54-56 and as support for catalysts.57,58 If spatially demanding dendrons are attached to a polymeric backbone, the polymer can be forced from a random-coil conformation to a stretched cylindrical.44,46 The multifunctional surface of these dendronized cylinders can be addressed and because of the potentially high bending modulus of these materials,44 dendronized polymers can be envisioned as molecular reinforcements in, for example, coating applications.

2.5.1 Synthesis of Dendronized Polymers The first synthetic route to dendronized polymers was described in 1987 in a patent by

Tomalia et al.59 and since then considerable synthetic effort has been devoted to developing new and efficient routs for these novel materials. Figure 10 displays the two main routes to attaining dendronized polymers.

Introduction

9

Figure 10. The macromonomer route (left), and the graft-onto route (right) to dendronized polymers.

In the macromonomer route, dendrons are linked to monomers that contain a polymerizable group either by a convergent or divergent methodology. The macromonomers are then polymerized, forming a dendronized polymer.44-46 The benefits of this approach are that the dendrons are accurately placed along the backbone. Several polymerization methods have been employed in the macromonomer route for example radical polymerization,47,60-64 reversible addition-fragmentation chain transfer (RAFT) polymerization,65 ring-opening metathesis polymerization (ROMP),66-68 ring-opening polymerization (ROP),55 Suzuki polycondensation,69-77 insertion polymerization,78 Stille coupling,79 Heck coupling,80 polycondensation,81 and atom transfer radical polymerisation (ATRP).82-86

The drawback of the macromonomer route is that larger dendrons may shield the polymerizable group and thereby inhibit the polymerization, resulting in either low molecular weight polymers or no reaction at all. Studies have addressed this problem, and propose that by increasing the distance between dendron and polymerizable group, the availability of the reactive group will increase. However, recent studies indicate that the problem of inhibition may be related only to the concentration of the monomer, if the concentration of monomer is kept high enough, high degrees of polymerization can be reached.87

In the ‘graft-onto’ route preformed dendrons are attached to a polymeric backbone. Both convergent and divergent approaches have been employed.44,46 The ‘graft-onto’ route may suffer the drawback of incomplete coupling steps due to steric crowding of the dendrons.44,46,88 To circumvent this problem, large excesses of coupling agent and long reaction times must be employed. The large excesses may lead to purification problems of the product. Divergent approaches to dendronized polymers utilizing either benzylidene-2,2-bis(methoxy) propanoic anhydride or acetonide-2,2-bis(methoxy) propanoic anhydride allow for purification of large excesses of coupling agent by simple extractions. 55,89-92 The benefit of combining the ‘graft-onto’ route with a controlled polymerization technique is that narrowly distributed dendronized polymers emanating from the same backbone can be produced with ease.

Experimental

3 Experimental

3.1 Instrumentation COSY-, HMQC-, DEPTH-, 1H- and 13C-NMR spectra were recorded on a Bruker AM 400

using DMSO-d6, CDCl3, MeOD, and Acetone-d6 as solvents. The solvent signal was used as internal standard.

Size exclusion chromatography (SEC) using THF (1.0 ml min-1) as mobile phase was performed at 35 °C using a Viscotek TDA Model 301 equipped with a GMHHR-M column with TSK-gel from Toshop Biosep, a Viscotek VE 5200 SEC Autosampler, a Viscotek V 1121 SEC Solvent pump and a Viscotek VE 5710 SEC Degasser. A universal calibration method was created using broad and narrow linear polystyrene standards.93 Correction for the flow rate fluctuation was made by using THF as an internal standard. Viscotek Trisec 2000 version 1.0.2 software was used to process data.

Molecular weights and polydispersity were determined by SEC on a Waters 6000A pump, a PL-EMD 960 light scattering evaporate detector, two PL gel 10 um mixed B columns (300 x 7.5 mm) from Polymer Labs and one Ultrahydrogel linear column (300 x 7.8 mm) from Waters. DMF was used as solvent at a flow rate of 1.0 ml min-1, preheated to 70 °C. Linear polyethylene oxides, ranging from 620 to 760 000 g mol-1 were used for calibration.

SEC was conducted in H2O (0.5 ml min-1, 0.1 M NaNO3) at 25 °C using a Rheodyne manual injector (200 µL loop), a Waters HPLC pump equipped with a in-line (elutant) filter (Millipore 25 mm DuraporeTM 0.1 µm), a DAWNTM DSP MALLS detector (laser operating at 633 nm), a Wyatt Technology OptilabTM DSP differential refractometer (laser operating at 633 nm, p10 cell) concentration detector, and five UltrahydrogelTM linear 7.8*300 mm columns. ASTRA software was used for evaluation.

The rheological measurements were performed on an ARES Rheometer from TA Instruments, DE, USA. The tests were performed in dynamic mode using a parallel plate configuration. The plates had a diameter of 8 mm. The sample was first molten between the plates at 120 °C, to ensure good contact between the plates and sample and also to ensure a uniform thickness. The sample was held at this temperature for 10 min and then cooled to 80 °C where the sample was let to equilibrate. The thickness of the samples were between 0.3-0.6 mm. Dynamic frequency sweep tests were performed between 0.1 rad s-1 and 200 rad s-1 at 80 °C, using a strain between 1 and 4 %, staring from the high frequency range. Strain sweep tests were conducted to ensure that the measurements were conducted in the linear viscoelastic region.

Differential scanning calorimetry studies were performed on a Mettler Toledo DSC820 equipped with a Mettler Toledo Sample Robot TSO801RO calibrated using standard procedures. The heating and cooling rates were 10 °C min-1. The Tg and Tm were determined during the second heating run.

1H-NMR self-diffusion measurements were performed on a Bruker DMX200 spectrometer equipped with a Bruker pulsed-field-gradient diffusion probe with a maximum gradient field of 9.6 T/m. The 90° pulse length for the 5 mm i. d. probe was 4.5 µs and the temperature was set to and controlled at 22 °C. The longitudinal relaxation experiments were carried out by the conventional inversion recovery experiment with 16 delay times, yielding data with an estimated accuracy of 5 %. The diffusion experiments were performed by the conventional stimulated echo sequence with 16 equidistant gradient steps up to 4 T/m. Fitting the conventional Stejskal-Tanner expression to the diffusional decays provided us with nominal diffusion coefficients that were calibrated to their corrects values by diffusion data obtained in water samples under identical conditions.

10

Experimental

Diffusion NMR measurements were also performed on a Varian UNITYINOVA spectrometer operating at 300 MHz for protons and equipped with a pulsed-field-gradient probe. The temperature was set and controlled at 22 °C. Self-diffusion measurements were carried out with a stimulated echo sequence using a delay time of 20 or 200 ms and 30 linearly incremented gradient strengths. The self-diffusion coefficients were calculated by plotting the signal intensities against the gradient strength, calibrated with a water sample at 22 °C.

Absorption measurements were performed at room temperature with a WPA S2000 Lightwave UV/Vis diode-array spectrophotometer.

MALDI analysis was performed using a Bruker Reflex III MALDI-MS instrument, equipped with a N2-laser, 337 nm (Bruker Daltonik GmbH, Bremen, Germany). All mass spectra have been obtained in reflectron mode. The ion optics was optimized to give good resolution for the molecular weight region of interest. Calibration was performed in order to secure good mass accuracy. As for the samples, solutions of 2-5 mM in THF were prepared. The matrices utilized were either trans-3-indoleacrylic acid (t3iA) or 2,5-dihydroxybenzoic acid (DHB). Matrix solutions were prepared as 0.1 M solutions in THF. The samples were prepared both as sample-matrix solutions and as sample-matrix-NaTFA- or LiTFA solutions, employing a 0.1 M of either NaTFA- or LiTFA solution in THF. The preparation protocol included mixing of 0.5-1.0 µL of sample with 10 µL of matrix and/or 0.5-1.0 µL of the cationization agent. Then 0.2-0.4 µL of the mixture was spotted on the MALDI target and was left to crystallize in room temperature. Normally 50 pulses were acquired for each sample. In order to achieve good mass accuracy and resolution the analysis was performed at the laser threshold of each individual matrix/sample combination. The sample molecules were also analyzed with the above stated instrumental parameters in laser desorption mode (without any matrix being present in the preparation).

MALDI analysis was also performed on a Bruker UltraFlex MALDI-TOF MS with SCOUT-MTP Ion Source (Bruker Daltonics, Bremen) equipped with a N2-laser (337 nm), a gridless ion source and reflector design. All spectra were acquired using a reflector-positive method with an acceleration voltage of 25 kV and a reflector voltage of 26.3 kV. Calibration was performed in order to secure good mass accuracy. As for the samples, solutions of 2-5 mM in THF were prepared. The matrix utilized was 9-Nitroanthrazene. Matrix solutions were prepared as 0.1 M solutions in THF. The samples were prepared as sample-matrix-AgTFA solutions, employing a 0.1 M of AgTFA solution in THF. The preparation protocol included mixing of 0.5-1.0 µL of sample with 10 µL of matrix and/or 0.5-1.0 µL of the cationization agent. Then 0.2-0.4 µL of the mixture was spotted on the MALDI target and was left to crystallize at room temperature. Normally, 50 pulses were acquired for each sample. In order to achieve good mass accuracy and resolution the analysis was performed at the laser threshold of each individual matrix/sample combination.

The infrared spectra were recorded on a Perkin-Elmer Spectrum 2000 FTIR equipped with a MKII Golden GateTM, Single Reflection ATR System from Specac Ltd, London UK. The ATR-crystal was a Diamond 45° ATR Top Plate. The parallel and perpendicular spectra were obtained with a Perklin-Elmer gold wire polarizer. 32 scans were recorded for each direction of the samples with a resolution of 4 cm-1.

Optical microscopy were performed on a Leitz Ortholux POL BK II optical microscope equipped with crossed polarizers and a Mettler Hot Stage FP 82HT controlled by a Mettler FP90 Central Processor. Microscopic images were recorded under isothermal conditions by a Leica DC 300 CCD camera and the images were analyzed with Leica IM50 software. Measurements of the structures were performed on a computer using a calibration scale.

Atomic force microscopic (AFM) images were recorded on a CSM Instruments Atom Force Microscope. Imaging was performed in non-contact mode in air using a Pointprobe

11

Experimental

Plus probe with a nominal spring constant of ~ 0.15 Nm-1 and a resonance frequency of 11–12 kHz. The length of the cantilever was 452 µm and the radius was narrower than 7 nm. Analysis of the images was performed in CSM Instruments ImagePlus v.3.1.10.

X-ray diffraction (XRD) was performed on a Philips PW 1710 θ-θ diffractometer, λ = 1.54060 Å (CuKα1, germanium monochromator).

Continuous wave fluorescence spectra were recorded using a Hitachi F-4500 spectrometer equipped with a Xe-lamp. Time-resolved measurements at selected emission wavelengths were recorded using an IBH 5000 spectrometer equipped with emission monochromator (5000M) and the TBX-04 picosecond photon detection module. A laser diode (NanoLed 07) operating at 403 nm was used as excitation source (ca 100 ps width, operating at 1 MHz). The life-time decays were measured sing time-correlated single photon counting along with the Data Station v 2.1 software for running the spectrometer and deconvolution and analysis of decays. The system also allowed variation of excitation and emission polarization, thus enabling the determination of time-resolved anisotropy decays.

Contact angle measurements were conducted on a KSV instruments CAM 200 equipped with a Basler A602f camera, using 5 µL droplets of MilliQ water. The water contact angels were determined using the CAM software.

Chromatography purifications were performed either by medium-pressure liquid chromatography (MPLC), or flash chromatography.

3.2 Materials N-Propyl-2-pyridylmethanamine was prepared according to a procedure described by

Haddelton et al.39 from n-propylamine and pyridine-2-carboxaldehyde. Dimethylamino-pyridinium-4-toluenesulfonate (DPTS) was synthesized according to a procedure described by Moore and Stupp.94 Cu(PPH3)3Br was prepared as described by Kintigh et al.95 6-azidohexanol, 6-azidohexyl-G#1-acetonide, 6-azidohexyl-G#1-OH, 6-azidohexyl-G#2-acetonide, 6-azidohexyl-G#2-OH, 6-azidohexyl-G#3-acetonide, 6-azidohexyl-G#3-OH, and 6-azidohexyl-G#4-acetonide was prepared according to literature procedures.4,5 2,2-Bis(methylol) propionic acid (bis-MPA) was kindly supplied by Perstorp AB, Sweden. The synthesis of benzyl protected bis-MPA was prepared according to the procedure developed by Hult et al.,96 the synthesis of acetonide-2,2-bis(methoxy) propionic acid was conducted according to literature procedures,97 and the synthesis of acetonide-2,2-bis(methoxy) propionic anhydride, which is used as a generic building block for divergent growth, is described elsewhere.91,98 All other reagents and solvents were used as received.

12

Results and Discussion

13

4 Results and Discussion A more detailed description of the synthetic methods employed to achieve the dendritic

porphyrins and the dendronized polymers are found in the appended papers.

4.1 Synthesis of Dendritic Porphyrins (Paper I) Metal containing dendron decorated porphyrins have been utilized for the non-covalent

assembly of dendronized polymers.22 In order to synthesize these structures a versatile route to the corresponding dendron decorated porphyrins must be developed. The effect of dendron encapsulation on the properties of a porphyrin dye is also important to investigate if new optical power limiting materials are to be developed.

4.1.1 Porphyrin Synthesis In order to investigate the effect of dendrimer decoration on the properties of a dye, a set

of 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,-23H-porphine cored dendrimers was synthesized. This porphyrin was chosen because it has been used in other studies on dendrimer encapsulation and is commercially available. Two sets dendritic porphyrins were synthesized, one set consisting of the free-base porphyrin (TPPH2) and one set with zinc cored porphyrin (TPPZn). Initially, two less successful synthetic procedures were tested.

The first one involved the coupling of preformed dendrons to the porphyrin core by a convergent methodology. This method worked well for the first and second generation dendrons but the purification procedures employed were tedious. With the third generation dendrons, only three out of the four phenolic groups could be reacted, probably due to steric congestion of the fourth phenolic group.

An attempt to grow the dendrimers straight from the porphyrin core was also tested. This effort also failed due to the uncontrolled hydrolysis of the phenolic ester bond between the dendron and the core during the acidic deprotection of the acetonide group.

Instead a propanol spacer was attached in the first synthetic step to the porphyrin by reacting the phenols with 3-bromo-1-propanol (Scheme 1). This was done in order to create a more hydrolytically stable ester bond. The bis-MPA based dendrimers were then grown in a divergent fashion by reacting the aliphatic hydroxyls with the acetonide protected anhydride of bis-MPA. The acetonide protective groups was removed by acidic deprotection with 2M H2SO4

99 to retrieve the hydroxyl functionality and further reacted with the anhydride building block. By this approach, dendrimers up to the fifth generation were obtained (Figure 11).


14

O

O O

O

O O

O

NN

NH

HN

OHHO

OHHO

Br OH NN

NH

HN

OO

OO

OH

HO

HO

OH

O

O

O

NN

NH

HN

OO

OO

O

O

O

O

O

O

O

O

O

O

O

O

O

O

OH

OH

NN

NH

HN

OO

OO

O

O

O

O

O

HO

HO

O

OH

OH

O

HO

HO

a

b

c

HO-G#0-prop-TPPH2

HO-G#1-prop-TPPH2 Acetonide-G#1-prop-TPPH2

TPPH2

Scheme 1. Spacer addition route to the porphyrin-cored bis-MPA dendrimers. Conditions: a) K2CO3, 18-crown-6, DMF, Reflux. b) Pyridine, DMAP, CH2Cl2, RT. c) THF, 2M H2SO4, RT.


15

4.1.2 Characterization of the Dendritic Porphyrins The two sets of dendritic porphyrins were characterized using size exclusion

chromatography (SEC). Table 1 depicts the molecular weights and polydispersities obtained. The observed molecular weights agree very well with the theoretical ones and the PDI are low for the dendritic porphyrins up to the fourth generation. For the two fifth generation dendrimers the PDI is somewhat higher, indicating small imperfections in their structures. These structural defects could arise from degradation or non-quantitative coupling in the last coupling step. Dendrimer synthesis utilizing the divergent methodology requires a larger number of reactions for each generation to form. Therefore, it is more likely that defects are obtained when synthesizing high generation dendrimers compared to lower generation dendrimers. Additionally, the sterical crowding of the dendrimer surface will reduce the availability of the hydroxyl groups. Table 1. Characterization of the porphyrin-cored bis-MPA dendrimers.

Compound Mwa (g/mol) Mn

b (g/mol) PDIb θc (ns) V (Å3) rd (Å)

HO-G#0-prop-TPPH2 911 700 1.04 0.41 3400 11

Acetonide-G#1-prop-TPPH2 1536 1100 1.03 0.57 4700 13





HO-G#0-prop-TPPZn 974 500 1.05 0.42 3500 11

Acetonide-G#1-prop-TPPZn 1599 1400 1.03 0.57 4700 13





a Theoretical molecular weight. b SEC with universal calibration. c Rotational correlation time from polarization anisotropy decay data. d Radius calculated assuming spherical symmetry.


16

Characterization of the dendritic porphyrins was also attempted using Matrix Assisted Desorption Ionization Time of Flight (MALDI-TOF). Good correlation between the theoretical molecular weight and the observed was obtained for the porphyrin dendrimers up to the second generation. At higher generations fragmentation started to occur, most probably due to the loss of acetonide groups. The fragmentation increased with increasing generation and for the fifth generation dendrimers only a broad peak was observed. The loss of the acetonide groups is most likely an effect of the acidic matrixes employed. Similar fragmentation behavior for dendritic porphyrins has been reported by other groups.100

OO

O O

O

O

OO

OO

O O

O O

O

O

OO

OO

OO

O

O

O

OO

O O

OO

O

OOO

OO

O

O

O

O

O

O

OO

O

OO

OO

O

O

OO

O O

OO

OO

O

O

OO

OO

O O

O

O

O

O O

OO

OOO

O OO

O O

O

O

O

O

OO

OO

O

OO

O

OO

OO

O

OO

O

OO

O

O

OO

OO

O

O

O

O

OO

O

OO

O

O

OO

O

OO

O

OO

O

OO

OO

OOO

OOO

O

O

OO

O

O

O

O

OO

O

O

OO

OO

O

O

O

O

OO

O

OO

O

O

OO

O

OO

O

OO

OO

O

OO

OOO

OOO

O

O

O O

OO

O

OO

O

OO

O

O

O O

O O

O

O

O

O

OO

O

OO

O

O

OO

O

O O

O

O O

OO

O

OO

OO O

OO O

O

O

OO

O

OO

O

OO

O

O

O O

O O

O

O

O

O

OO

O

OO

O

O

OO

O

O O

O

O O

OO

O

OO

OO O

OO O

O

O

O

O

NH N

HNNO

OO

OO

O

O

OO

O O

OO

OO

O

O

OO

OO

OO

O

O

O

O O

OO

OO

O

O OO

OO

O

O

O

O

OO

OO

O

O O

O O

O

O

OO

OO

O O

O O

O

O

OO

OO

OO

O

O

O

OO

O O

OO O

OOO

OO

O

O

O

O

O

O

OO

O

OO

Acetonide-G#5-prop-TPPH2 Figure 11. A fifth generation free base porphyrin cored dendrimer.


17

To elucidate the structure of the dendritic porphyrins in solution (THF), polarization anisotropy decay data from fluorescence measurements where obtained. From the rotational correlation time, θ, and the Stokes-Einstein-Debye relationship

TkV Bh /ηθ = (1)

where Vh is the hydrodynamic volume of the molecule, η is the viscosity of the solvent (THF, 0.49 cP),101,102 kB is the Boltzmann constant, T is the absolute temperature, the size of the dendritic porphyrins could be calculated. If one assumes a spherical geometry the radii of the dendrimers can be calculated (Table 1). Figure 12 displays the radius of the dendritic porphyrins as a function of generation. The radii of the molecules increase with increasing generation, and the radii of the zinc cored porphyrins are slightly larger than the free base porphyrins. This is probably an effect of the increased difficulty in measuring the rotational correlation times of the zinc cored porphyrins. The continuing increase in radii with higher generation of the molecules in Figure 12 suggests that the dendrimers has not reached a size where structural collapse occurs.25

Figure 12. Hydrodynamic radius as a function of generation.

If one compares the size of these dendritic porphyrins with porphyrins decorated with Fréchet-type dendrons (benzyl ether), the bis-MPA dendrimers of the same generation are smaller.25


18

4.2 Dendronized Poly(hydroxyl ethyl methacrylate) (Paper II)

4.2.1 Synthesis of the macromonomers The macromonomers used in this study were synthesized according to Scheme 2. The

anhydride of bis-MPA was used as generic building block for the divergent growth of the dendritic monomers. The first generation macromonomers (HEMA-G#1-Ac) was deprotected by stirring the monomer in methanol and in the presence of acidic DOWEX resin,97 hence activating it for further dendron growth. The coupling/deprotection reactions proved to be high yielding, facilitating monomer synthesis on a large scale.

O

OOH O

O O

O

O O

O

OO

OOH

OHO

OO

OO

O O

O

O

O

O

O

O

OO

OO

OO

OO

OO

OO

O

O O

O

O O

O

b

a

a

HEMA HEMA-G#1-Ac

HEMA-G#1-Ac HEMA-G#1-OH

HEMA-G#2-Ac

Scheme 2. Synthesis of HEMA-G#1-Ac, HEMA-G#1-OH, HEMA-G#2-Ac. Conditions: a) Pyridine, DMAP, CH2Cl2. b) DOWEX H+, MeOH, 40 °C.

4.2.2 Polymerization of the macromonomers via ATRP In the first attempt to polymerize HEMA-G#1-Ac, Cu(I)Br 2,2'-dipyridyl was used as

halogen ligand system. This system is one of the most used halogen/ligand system for ATRP, but rendered polymers with polydispersities in the range of 1.3-1.5 (entries 1-5 in Table 2).31 To achieve a more controlled polymerization, a system utilizing Cu(I)Br, Cu(II)Br2, N-propyl-2-pyridylmethanimine were utilized (Scheme 3). The Cu(II)Br2 serves as deactivator for the polymerization, lowering the concentration of propagating radicals, hence suppressing side-reactions. N-propyl-2-pyridylmethanimine has been reported as versatile and efficient ligand for ATRP of methylmethacrylates.39 This system of Cu(I)Br, Cu(II)Br2, and N-propyl-2-pyridylmethanimine resulted in polymers with considerably lower PDI (1.1-1.2), and the results are summarized in Table 2 (entries 6-8 in Table 2). The molecular weights of the polymers obtained by this system agree fairly well with the theoretical ones, and further discussion about the molecular weights obtained for the different polymerizations is given in Section 4.2.3.


19

O

OO

O O

O

O

OO

O O

O

OO

O

OO

O

O

O

Br

O

OBr

OO

OO

O O

O

O

Br

O

OBr

OO

OO

O O

O

OO

O

OO

a

b

N

N

N

N

n

m

HEMA-G#1-Ac

HEMA-G#2-Ac p-HEMA-G#2-Ac

p-HEMA-G#1-Ac

Scheme 3. ATRP of HEMA-G#1-Ac, and HEMA-G#2-Ac. Conditions: a) Bulk, 60 °C, Cu[I]Br, Cu[I]Br2. b) Toluene, 60 °C, Cu[I]Br, Cu[II]Br2.

An investigation of the polymerization kinetics for the first generation macromonomer

revealed that the polymerization follows first-order kinetics for low conversions. Figure 13 depicts the kinetic plot for the polymerization of HEMA-G#1-Ac with the system, ethyl-2 bromoisobutyrate (EBiB) Cu(I)Br, Cu(II)Br2 and N-propyl-2-pyridylmethanimine. As seen in Figure 13 the reaction rate is lower for the Cu(I)Br, Cu(II)Br2, N-propyl-2-pyridylmethanimine system, compared to the system utilizing Cu(I)Br and 2,2'-dipyridyl, but the N-propyl-2-pyridylmethanimine system is more linear.

Figure 13. First order kinetic plots showing ln[M]0/[M] vs. time for, (∆) HEMA-G#1-Ac [M]:[I]:[Cu(I)]:[Cu(II)]:[Lig] = 25:1:1:0.1:2, and (●) HEMA-G#1-Ac [M]:[I]:[Cu(I)]:[Cu(II)]:[Lig] = 25:1:1:-:2.


20

In the case of the HEMA-G#2-Ac the polymerization was not possible to conduct in bulk

because of the high viscosity of the monomer. Schlüter et al.103 have suggested that radical polymerization of viscous macromonomers is difficult if the monomer concentration is to low (<~45%), and therefore the polymerization was conducted in a 50 % (w/w) mixture of toluene to monomer (Scheme 3). The polymerization of HEMA-G#2-Ac was mediated with the same system developed for HEMA-G#1-Ac and resulted in a polymer with PDI of 1.2 (entry 9 in Table 2).

A kinetic investigation of the polymerization of HEMA-G#2-Ac was also conducted. Figure 14 display the polymerization utilizing EBiB, Cu(I)Br, Cu(II)Br2, N-propyl-2-pyridylmethanimine, and toluene, in the ratio, [M]:[I]:[Cu(I)]:[Cu(II)]:[Lig]:[Tol] = 25:1:1:0.1:2:25. The kinetics deviates slightly from linearity, which is thought to be a result of initial termination reactions, or an inefficient initiation. The molecular weight of the polymer is reported in Table 2, where it can be seen that the obtained molecular weight is considerably lower than the theoretical value. Further discussion about the molecular weights obtained for the polymerization is given in Section 4.2.3.

Figure 14. First order kinetic plots showing ln[M]0/[M] vs. time for, HEMA-G#2-Ac [M]:[I]:[Cu(I)]:[Cu(II)]:[Lig]:[Tol] = 25:1:1:0.1:2:25.

Scheme 4 depicts the synthetic route utilized for obtaining dendronized tri-block copolymers. First methyl methacrylate was polymerized by ATRP from a difunctional initiator and further used as a macroinitiator for the polymerization of the first generation monomer. By this methodology a dendronized tri-block copolymer was synthesized in two steps.104 The methyl methacrylate was polymerized by ATRP utilizing Cu(I)Br, Cu(II)Br2, and 2,2'-dipyridyl as a halogen/ligand system. The reaction was terminated by adding a saturated solution of Cu(II)Br2 suspended in toluene, to ensure bromine functionalized end-groups. The macroinitiator had a molecular weight of 7900 g mol-1 and a PDI of 1.3 (entry 10 in Table 2). HEMA-G#1-Ac was then polymerized from the macroinitiator, utilizing Cu(I)Br, Cu(II)Br2, and 2,2'-dipyridyl as halogen/ligand system. This system was chosen because of the higher reaction rate compared to the N-propyl-2-pyridylmethanimine system. The resulting tri-block dendronized polymer had a molecular weight of 36000 g mol-1, slightly higher than the theoretical value of 30800 g mol-1 and with a PDI of 1.2 indicating good control of the polymerization (entry 11 in Table 2).

21

O O

OBr

OBr

OO

aO O

OOBrBr

OO

OO

O O

OOBrBr

OO

OO

O

OO

O O

Ob

O O

OO

OO

OO

Br Br

OO

OO

OOO O

O OO O

DiPMMA

DiPMMA

HEMA-G#1-Ac G#1-b-PMMA-b-G#1

4.2.3 Characterization by Size Exclusion Chromatography The size exclusion chromatography results for the polymers obtained by ATRP of the

macromonomers are presented in Table 2. The data were obtained from a THF-SEC utilizing both conventional and universal calibration. In the case of universal calibration, the apparatus is calibrated using both narrow and broad polystyrene standards, and gives a more accurate molecular weight determination compared to conventional calibration for polymer with complex architectures.93 It is known that conventional calibration underestimates the molecular weights of branched polymers such as dendrimers.105 However, the universal calibration method requires a known concentration of polymer, which limits this technique to worked-up polymers. In Table 2 it can be seen that the molecular weights obtained by conventional calibration is lower than the results obtained by universal calibration for the dendronized polymers. This is effect may be attributed to higher molar mass per length unit for dendronized polymers compared to the linear standards. However, the more compact rigid structure of the polymer chain at higher generations results in higher hydrodynamic volume, which in turn results in an overestimation of the molecular weight.44 Therefore, molecular weight determination of dendronized polymers using SEC should be interpreted with care.

In the case of the kinetic investigations of the first and second generation monomers, a conventional calibration method was used. As seen in Table 2, the polydispersities obtained in the initial attempts to polymerize the first generation monomer are broad (entries 1-2 Table 2) and the molecular weights obtained are higher than the theoretical. This indicates that either a significant amount of termination occurs, or that the initiation is poor. By lowering the polymerization temperature from 90 °C to 60 °C the PDI of the resulting polymers were lower (entries 3-5 Table 2), but the obtained molecular weights still deviate significantly from the theoretical ones. By changing the ligand from 2,2'-dipyridyl to N-propyl-2-pyridylmethanimine, and adding Cu(II)Br2 as deactivator, polymers with much lower polydispersities, and molecular weights closer to the theoretical (entries 6-8 Table 2) were obtained.

Scheme 4. Synthesis of a dendronized tri-block copolymer. Conditions: a) 2,2´-Dipyridyl, 90 °C, Cu[I]Br, Cu[II]Br2. b) Toluene, 60 °C, 2,2´-Dipyridyl, Cu[I]Br, Cu[I]Br2.



22

Table 2. Summary of SEC results for the polymerizations.

Polymerization [M]:[I]:[Lig]:[Cu(I)]:[Cu(II)]:[Sol] Monomer Mn aim (g/mol) Mna (g/mol) Mn

b (g/mol) PDIa PDIb

1 [50]:[1]:[2]:[1]:[-]:[50]c, f HEMA-G#1-Ac 28800 63920 - 1.5 -

2 [100]:[1]:[2]:[1]:[-]:[50]c, f HEMA-G#1-Ac 28800 67600 - 1.8 -

3 [50]:[1]:[2]:[1]:[-]:[50]c, e HEMA-G#1-Ac 14500 - 6300 - 1.3

4 [50]:[1]:[2]:[1]:[0.1]:[50]c, e HEMA-G#1-Ac 14500 2340 - 1.5 -

5 [50]:[1]:[2]:[1]:[0.1]:[50]c, e HEMA-G#1-Ac 14500 23700 - 1.5 -

6 [50]:[1]:[2]:[1]:[0.1]:[-]d, e HEMA-G#1-Ac 14500 11700 - 1.2 -

7 [25]:[1]:[2]:[1]:[0.1]:[-]d, e HEMA-G#1-Ac 7300 13300 - 1.2 -

8 [50]:[1]:[2]:[1]:[0.1]:[-]d, e HEMA-G#1-Ac 14500 18200 6800 1.1 1.1

9 [25]:[1]:[2]:[1]:[0.1]:[-]d, e HEMA-G#2-Ac 14200 - 6200 - 1.2

10 [25]:[1]:[2]:[1]:[0.1]:[-]c, f MMA 5400 7900 - 1.3

11 [40]:[1]:[2]:[1]:[0.1]:[40] (each side)c, e HEMA-G#1-Ac 30800 36000 - 1.2

a Mn obtained by SEC using universal calibration (UC) in THF. b Mn obtained by SEC using conventional calibration (CC) in THF. c 2,2'-dipyridyl. d N-propyl-2-pyridylmethanimine. e 60 °C. f 90 °C.


23

4.3 Dendronized Poly(hydroxyl ethyl methacrylate) via the ‘Graft-onto’ Route (Paper II)

4.3.1 Acetonide, Acetate and Hydroxyl Functional Dendronized Polymers The ‘graft-onto’ route for attaining dendronized polymers was also explored in this work.

First a large amount of the first generation dendronized polymer was prepared utilizing the N-propyl-2-pyridylmethanimine, Cu(I)Br, and Cu(II)Br2 system previously developed. The acetonide groups of this polymer were then removed by stirring in a solution of acidic DOWEX resin suspended in MeOH and THF at 50 °C (Scheme 5).97 The product, p-HEMA-G#1-OH was further purified by precipitating the crude polymer from THF in hexane. The second generation acetonide protected polymer p-HEMA-G#2-Ac was synthesized by reacting the OH groups of p-HEMA-G#1-OH with the acetonide protected anhydride of bis-MPA according to the procedure outlined by Fréchet et al.55,89 The coupling was conducted in a mixture of pyridine and DMF89 utilizing a large excess of coupling agents. Earlier reports of esterification of dendronized polymers by using the benzylidene protected anhydride of bis-MPA have suggested the availability of the OH groups is increased if DMF is employed as a co-solvent. In our initial attempts of obtaining dendronized polymers by using the acetonide protected anhydride of bis-MPA the same was observed.

O

OBr

OO

OO

O O

O

OBr

OO

OO

O O

O

OO

O

OO

n m

O

O O

O

O O

O

O

OBr

OO

OO

OH OH

n

O

OBr

OO

OO

O O

O

OHOH

O

HOHO

m

a b

ab and a repeated

O

O O

O

O O

O

O

O O

b

p-HEMA-G#1-Ac

p-HEMA-G#1-OH

p-HEMA-G#2-Ac

p-HEMA-G#2-OH

p-HEMA-G#3-Ac

p-HEMA-G#3-OH

p-HEMA-G#4-Ac

p-HEMA-G#2-Acetate

p-HEMA-G#3-Acetate

p-HEMA-G#4-Acetate

Scheme 5. Divergent growth of dendronized polymers. Conditions: a) DOWEX H+, MeOH, THF, 50 °C. b) DMF, Pyridine, DMAP, CH2Cl2, RT.

The coupling reactions were allowed to proceed for a long time (60-100 h), after which the conversion of the OH groups was quantified by NMR. The excess acetonide protected anhydride of bis-MPA was removed according to procedures outlined in previous publications.84,89,98 The crude product was purified by precipitation in MeOH from CH2Cl2.


24

By employing the same methodology dendronized polymers up to the fourth generation with acetonide protective groups and hydroxyl groups were produced.

A set of dendronized polymers with acetate end-groups was accomplished following a similar procedure as for the acetonide functional materials (Scheme 5). The hydroxyl functional polymer was dissolved in a mixture of DMF and pyridine and reacted with acetic anhydride in a DMAP catalyzed esterification. The crude product was purified by extraction and precipitation in hexane from CH2Cl2.

4.3.2 Aliphatic Hexadecyl Functional Dendronized Polymers In an effort to further tailor the functionality of end-groups of the dendronized polymers

aliphatic hexadecyl chains was introduced. Scheme 6 depicts the synthetic route employed.

OO

OHOH

Cl

O

C15H31

a

OO

OO

O

OBr

OO

OO

OH OH

m

O

C15H31

O

C15H31

bHO

O

OO O

C15H31

O

C15H31

cCl

O

OO O

C15H31

O

C15H31

dCl

O

OO O

C15H31

O

C15H31

O

OBr

OO

OO

O O

m

O

OO

O

C15H31O

C15H31

O

OO

O

C15H31O

C15H31

p-HEMA-G#1-OH

p-HEMA-G#2-C16

p-HEMA-G#3-C16

p-HEMA-G#4-C16

Scheme 6. Hexadecyl modification of the dendronized polymers. Conditions: a) Trietylamine, DMAP, CH2Cl2, 0 °C. b) Pd/C, H2, MeOH, CH2Cl2, RT. c) Oxaylchloride, DMF (catalytic amount), CH2Cl2, RT. d) Triethylamine, DMAP, DMF, Pyridine, CH2Cl2, RT.

First benzylidene protected bis-MPA was reacted with palmiotylchloride. The protective group of the aliphatic functionalized bis-MPA was then removed in order to retrieve the carboxylic acid functionality.106 The carboxylic acid functionality was then transformed to an acid chloride by reacting it with oxayl chloride in a similar manner outlined by Hult et al.96 The coupling agent was then reacted with the hydroxyl functional dendronized polymer a mixture of DMF, triethylamine, and pyridine to give the hexadecyl functional polymer. As in the case of the other coupling reactions, the reaction was allowed to proceed for a long time (80-100 h), and excess coupling agent was quenched by stirring with water. The crude product was purified by repeated extractions and finally precipitated in warm (40 °C) MeOH from CH2Cl2. By this approach dendronized polymers of generation two, three, and four with aliphatic hexadecyl functionality were obtained.


25

4.3.3 Characterization by Size Exclusion Chromatography Size exclusion chromatography of the divergently grown dendronized polymers was

performed on a THF-SEC, a DMF-SEC, a H2O-SEC, and the results are summarized in Table 3. The acetonide functional dendronized polymers increase in molecular weight for each coupling step while the polydispersity remained low. The observed molecular weights agree well with the theoretical ones for p-HEMA-G#2-Ac, but deviate more for the higher generation dendronized polymers. Similarly, the PDI of the acetate functionalized dendronized polymers remained low for each coupling. The molecular weight obtained agrees well with the theoretical value for p-HEMA-G#2-Acetate, but deviates more for the higher generation polymers. For the hexadecyl functional materials the polydispersity remains low for all materials synthesized. However the molecular weight obtained deviates significantly from the theoretical. This could be an effect of the unusual architecture of these polymers or due to sample-column interactions. The hydroxyl functional polymers aggregated in DMF as observed by DMF-SEC, resulting in an uncertain molecular weight determination. Therefore a H2O-SEC with a multi angle laser light scattering detector (MALLS) was used instead and the corresponding molecular weights were in good agreement with the theoretical. The polydispersity for p-HEMA-G#4-OH is higher compared to the lower generation samples. This could be an effect of p-HEMA-G#4-OH interacting more strongly with the columns, or the presence of some structural defects. Unfortunately the hydrodynamic volume of the p-HEMA-G#1-OH is too low for detection in the SEC-MALLS setup used, so no data on molecular weight and PDI could be obtained. Table 3. Summary of SEC results for the divergently grown dendronized polymers.

Compound Mncalc Mn SECa Mn SECb Mn SECc PDIa PDIb PDIc

p-HEMA-G#1-Ac - 13200 8500 - 1.2 1.2 - p-HEMA-G#1-OH 11400 - - - - p-HEMA-G#2-Ac 25700 25500 10000 - 1.2 1.2 - p-HEMA-G#2-OH 22000 - - 22600 - - 1.1

p-HEMA-G#2-Acetate 29700 30800 10700 - 1.2 1.2 - p-HEMA-G#2-C16 65500 98800 25300 - 1.1 1.1 - p-HEMA-G#3-Ac 50500 60900 16700 - 1.2 1.1 - p-HEMA-G#3-OH 43200 - - 44000 - - 1.1

p-HEMA-G#3-Acetate 58600 76700 17700 - 1.1 1.1 - p-HEMA-G#3-C16 130300 131200 25000 - 1.1 1.1 - p-HEMA-G#4-Ac 100300 134600 24300 - 1.1 1.1 - p-HEMA-G#4-OH 85600 - - 94400 - - 1.3

p-HEMA-G#4-Acetate 116300 148000 27700 - 1.2 1.2 - p-HEMA-G#4-C16 259600 227200 37300 - 1.2 1.2 -

a Mn obtained by SEC using universal calibration (UC) in THF. b Mn obtained by SEC using conventional calibration (CC) in THF. c Mn obtained by SEC-MALLS in H2O (0.1 M NaNO3), dn/dc (H2O, 0.1 M NaNO3, 293.15 K); p-HEMA-G#2-OH 0.1215 g/ml, p-HEMA-G#3-OH 0.1292, p-HEMA-G#4-OH 0.1293.


26

4.4 Dendronized Poly(norbornene) (Paper IV)

4.4.1 Synthesis of the dendron bearing monomers The dendron bearing norbornenes were synthesized in a similar manner as the HEMA

based macromonomers previously described in Section 4.2.1 (iterative ester couplings and deprotection reactions utilizing the acetonide protected anhydride of bis-MPA and acidic DOWEX resin). Scheme 7 depicts the synthetic approach to these monomers starting from the commercially available 5-norbornene-2-methanol (endo/exo mixture). The norbornene alcohol was chosen for two reasons; this compound has a large ring strain and can be polymerized by ROMP using Grubbs´ first and second generation catalyst at room temperature.107 Secondly, dendronized monomers based on this monomer can be synthesized in a few steps providing a relatively simple and quick route to these monomers.

OHO

O O

O

O O

Oa

O

O

O

O b

O

O

OH

OH a and b repeated

O

O O

O

O O

O

O O

OO

OO

O

O O

O

OO

O

O O

O

O

O

O

O

O

OO

OO

O

OO

O

OO

O

O

O O

OO

O

O O

O

O O

O

OO

Nor-G#1-Ac

Nor-G#1-OH

Nor-G#4-Ac Scheme 7. Synthesis of the dendron bearing norbornenes. Conditions: a) Pyridine, CH2Cl2, RT. b) DOWEX H+, MeOH, 50 °C.

4.4.2 Polymerization of the norbornenyl macromonomers Initially the second generation Grubbs´ catalyst (top in Scheme 8) was tested for the

polymerization of the first to fourth generation norbornenes. This catalyst was chosen since it has been reported to be successful for the polymerizing sterically demanding norbornenyl macromonomers.107 High generation dendron bearing monomers can be anticipated to be rather sterically congested monomers and we therefore choose to start by evaluating this catalyst. Scheme 8 depicts the polymerization reaction of the third generation monomer (Nor-G#3) and the SEC results are summarized in Table 4. As seen in Table 4 the polymerizations with this catalyst (entries 1-8 in Table 4) resulted in polymers with rather broad polydispersities (conventional calibration 1.3-3.3, universal calibration 1.3-13) and molecular weights higher than the theoretical, indicating poor control over the polymerization. Kinetic investigations of less sterically demanding monomers have shown that the molecular weight


27

obtained with the Grubbs´ type II catalyst system exceeds the theoretically calculated. These effects have been explained as a result of a higher rate of propagation to rate of initiation for the polymerization with this catalyst.108-110

RuCl

Cl

PCy3

PCy3Ph

or

NN

RuCl

Cl PCy3Ph O

O

OO O

O

O

O

O

OO

OO

O

O

O

O

O

O O

OO

Ph n

OO

OO O

O

O

O

O

OO

OO

O

O

O

O

O

O O

OO

a

Nor-G4-Ac p-Nor-G#4 Scheme 8. Polymerization of the dendron bearing norbornenes with Grubbs´ first and second generation catalyst. Conditions: a) 1.CH2Cl2 (dry), RT, 2. Ethyl vinyl ether, RT.

Because of the broad polydispersities of the resulting polymers obtained with the Grubbs´ type II catalyst the less active Grubbs´ type I catalyst was used instead. The resulting polymers, (entries 9-17 in Table 4) had comparably lower polydispersities (conventional calibration 1.1-1.3, universal calibration 1.2-3.7) and molecular weights lower than the theoretical. The yields of the polymers after precipitation were in between 40-60 % for all reactions. The experimentally lower molecular weight observed for these polymers most likely related to the lower activity of the endo isomer of the norbornene towards polymerization.107 However, the increasing size of the dendrons may also shield the polymerizable group and result in lower molecular weights. The theoretical molecular weight at a given conversion could not be determined due to overlapping peaks of the monomer and the polymer in the 1H-NMR spectrum. For all the polymers analyzed, a small high molecular weight shoulder in the SEC chromatograms was observed using the refractive index detector (conventional calibration). This shoulder was more pronounced when the more high molecular weight sensitive viscosity detector was used (universal calibration).


28

Table 4. Polymerization results obtained with Grubbs´ I (entries 1.8) and Grubbs II (entries 9-17). Entry Polymer [M]0/[I]0 Time [h] Mn Theo x 10-3 Mn x 10-3 c PDIc Mn x 10-3 d PDId

1 p-Nor-G#1 100 a 20 28 200.6 2.8 84.8 6.0

2 p-Nor-G#2 49 a 20 27 174.3 2.0 113.6 4.0

3 p-Nor-G#3 26 a 20 28 381.2 1.9 100.1 11.1

4 p-Nor-G#4 20 a 20 46 27.4 2.8 32.0 3.0

5 p-Nor-G#1 1426 a 20 400 849.5 1.3 3231 1.3

6 p-Nor-G#2 724 a 20 400 457.4 2.0 472.6 6.2

7 p-Nor-G#3 365 a 20 400 258.4 3.3 84.9 13.0

8 p-Nor-G#4 175 a 20 400 37.4 1.8 60.6 1.7

9 p-Nor-G#1 180 b 20 51 66.5 1.9 43.7 2.1

10 p-Nor-G#2 180 b 20 100 66.7 1.1 63.9 1.2

11 p-Nor-G#3 180 b 20 198 64.6 1.1 68.7 1.3

12 p-Nor-G#4 180 b 20 366 46.9 1.2 55.7 1.5

13 p-Nor-G#1 500 b 20 140 154.6 1.7 68.1 2.8

14 p-Nor-G#2 500 b 40 276 149.9 1.1 110.8 1.5

15 p-Nor-G#3 500 b 60 549 170.0 1.4 152.6 2.8

16 p-Nor-G#4 500 b 72 1093 129.1 1.4 125.3 3.7

17 p-Nor-G#4 500 b 72 1093 118.9 1.5 130.8 3.5

a Grubbs’ second generation catalyst, b Grubbs’ first generation catalyst, c Conventional calibration, d Universal Calibration.


29

4.5 Dendronized Triblock Copolymers (Paper V)

4.5.1 Synthesis of the dendron bearing acrylates Azido-functional dendrons were synthesized according to Scheme 9 starting from 6-

chlorohexanol, as previously described by Hawker et al.4 The first to fourth generation azido functional dendrons were subsequently reacted to the commercially available propargyl acrylate by copper(I) catalyzed [Cu(TPP3)3Br] “Click” in the presence of N,N-diisopropylethylamine.4 The coupling proceeded smoothly, and the crude monomers were purified by flash chromatography eluting with ethyl acetate and hexane, resulting in high yields after purification. By coupling the polymerizable group in the last step, the purification procedure of dendritic macromonomers is simplified compared to the divergent technique, since only one purification step with the polymerizable group present is necessary.

a bOCl N3

OH

O O

O

O O

O

N3O

OH

OO

O cN3

O

OOH

OH

O

OH d

NN

NO

O

O

N3O

OO

O O

O

O

O

O

O

OO

O O

O

O

O

O

O

b

O

O O

O

O O

O

Azido-C6H12-OH

Azido-C6H12-G#1-Ac Azido-C6H12-G#1-OH

Azido-C6H12-G#2-Ac

Acrylate-Triazol-C6H12-G#2-AcAcrylate-Triazol-C6H12-G#1-Ac

Acrylate-Triazol-C6H12-G#3-Ac

Acrylate-Triazol-C6H12-G#4-Ac

Scheme 9. Synthesis of the dendron bearing acrylates. Conditions: a) NaN3, DMSO, reflux. b) DMAP, Pyridine, CH2Cl2, RT. c) Methanol, DOWEX H+, 40 °C. d) DiPEA, Cu(TPP3)3Br, THF, RT.


30

4.5.2 Polymerization of the acrylate functional macromonomers The difunctional RAFT agent used as chain transfer agent (CTA) where synthesized in a

two step procedure as depicted in Scheme 10. Firstly, the intermediate CTA, was synthesized by a esterification between tri(ethylene glycol) and α-bromophenylacetic acid.111 The dithioester group of the CTA was introduced by first reacting phenyl magnesium bromide with carbon disulfide (CS2), followed by in situ addition of the difunctional α-bromoester.38,111

Br

O

OH HOO

OOH

Br

O

OO

OO

O

Br

a

MgBrb

S

SMgBr

S

O

OO

OO

O

S

S

S

c

OO

OS

S

dOO O

O

OS

OO

Sn

2

e

NN

NO

OO

O O

O

O

O

O

O

O

OO

O

O

O

O

SS

2

m

n

2

+

Br

O

OO

OO

O

Br

OO

OS

OO

Sn

2

NN

N

OO

OO

O O

O

OO

O

OO

Di-CTA

Di-CTADi-CTA-PMMA

Di-CTA-PMMA

Acrylate-triazol-C6H12-G#2-Ac

G#2-b-PMMA-b-G#2

Scheme 10. Polymerization of the dendronized monomers. Conditions: a) DCC, DPTS, DMAP, CH2Cl2, RT. b) CS2, THF, 40 °C. c) THF, reflux. d) AIBN, 70 °C. e) AIBN, benzene 60 °C.


31

The CTA was then used for the polymerization of methyl methacrylate in the presence of AIBN, resulting in polymers with narrow molecular weight distribution and two dithioester end groups (Table 5).

The first generation acrylate functional macromonomer (acrylate-triazol-C6H12-G#1-Ac) was polymerized from the difunctional PMMA macroCTA (entry 1 in Table 5). The polymerization was conducted in flame sealed glass vials at 60 °C. The polymerization was carried out with benzene as a solvent due to the high viscosity of the monomer. The first generation monomer reacted to high conversion (>85 %) in all polymerizations. As seen in Table 5 the PDI of the resulting polymers decreased with increasing conversion of the first generation monomer and theoretical and experimental molecular weight were in closer agreement for the polymers with higher conversion. Best control was obtained for the polymerizations conducted for 12 h which had PDI’s in the range of 1.2-1.3 and molecular weights corresponding to DP’s of 62-68 per arm.

Acrylate-triazol-C6H12-G#2-Ac was polymerized in the same manner as the first generation monomer, in a benzene solution and in the presence of AIBN. As shown in Table 5 the obtained conversions drops significantly compared to the lower generation monomer. The highest conversion was achieved after 24 h but the corresponding polymer had fairly high polydispersity (1.8). Therefore shorter reaction times were employed for the polymerization of this monomer, resulting in second generation triblock copolymers with better control. The best control was obtained for the polymerization that was conducted for 20 h which resulted in a G#2 triblock with PDI 1.1 and a molecular weight of 44000 g mol-1 which corresponds to a DP of 19 per arm. Similar observations regarding the lower reactivity of higher generation monomers have also been previously reported for ATRP of bis-MPA based monomers.82,85,112

Acrylate-triazol-C6H12-G#3-Ac also exhibited a lower reactivity compared to the lower generation macromonomers, with conversion not exceeding 12 % even after prolonged reaction times (84 h). The molecular weight obtained corresponds to a DP of ~ 8 repeating units per arm for the third generation triblock copolymers.

For acrylate-triazol-C6H12-G#4-Ac, very low conversions of the monomers were observed and the obtained molecular weights correspond to an oligomeric addition of the G#4 monomer (2-3 repeat units).

All dendronized triblock copolymers exhibited a small shoulder towards higher molecular weight on the SEC chromatograms, which was more pronounced when the more sensitive viscosity detector was employed (universal calibration). This shoulder is most likely due to bimolecular termination reactions.

Due to the high viscosity of the monomers, the polymerizations had to be conducted in increasing amounts of benzene. This in combination with the increasing molecular weight of the monomers results in a reduction of the concentration of available vinyl groups for the polymerization.87 This in turn may limit the polymerization.


32

Table 5. Polymerization results obtained. Entry Polymer [M]0/[I]0 Time [h] Conv [%] Mn Theo x 10-3 j Mn x 10-3 h PDI h Mn x 10-3 i PDI i

1 PMMA 666 5 56 37.3 34.5 1.2 31.5 1.2

2 PMMA 666 4 42 27.9 18.4 1.3 19.8 1.3

3 PMMA 666 4 41 27.2 17.7 1.3 18.5 1.3

4 G#1-b-PMMA-b-G#1 160 a 10 85 90.2 d 67.6 1.5 89.8 2.2

5 G#1-b-PMMA-b-G#1 160 a 12 94 96.1 d 90.2 1.2 84.0 1.7

6 G#1-b-PMMA-b-G#1 160 a 12 90 93.5 d 85.3 1.3 102.5 1.6

7 G#2-b-PMMA-b-G#2 160 b 24 34 55.5 e 42.4 1.8 64.1 2.5

8 G#2-b-PMMA-b-G#2 160 b 8 10 29.3 e 35.3 1.6 29.1 1.8

9 G#2-b-PMMA-b-G#2 160 b 20 19 40.2 e 44.0 1.1 41.8 1.2

10 G#3-b-PMMA-b-G#3 160 c 48 9 35.4 f 36.6 1.2 31.2 1.1

11 G#3-b-PMMA-b-G#3 160 c 84 12 41.2 f 39.3 1.2 27.0 1.2

12 G#4-b-PMMA-b-G#4 160 c 24 low - g 25.7 1.2 - -

13 G#4-b-PMMA-b-G#4 160 c 48 low - g 25.4 1.7 28.5 1.4

14 G#4-b-PMMA-b-G#4 160 c 72 low - g 29.5 1.2 34.7 1.2

a Entry 1 as macroinitiator, b Entry 2 as macroinitiator, c Entry 3 as macroinitiator, d G#1 monomer 409.49 g mol-1, e G#2 monomer 681.79 g mol-

1, f G#3 monomer 1226.29 g mol-1, g G#4 monomer 2315.59 g mol-1, h Conventional calibration, i Universal Calibration, j Theoretical molecular weight at the given conversion.


33

4.6 Bulk Properties of the Dendronized Polymers (Papers III, and IV)

4.6.1 Differential Scanning Calorimetry – Dendronized Poly(hydroxyl ethyl methacrylate)

The acetonide, hydroxyl and hexadecyl functional dendronized polymers were analyzed by differential scanning calorimetry (DSC). The glass transition temperature (Tg) values where determined from the second heating run (heating/cooling rate 10 °C min-1) and are reported as the inflexion point of the transition and are listed in Table 6. Similar to another study on dendronized polymers, the glass transition temperature increases with increasing size of the pendant dendrons,113 however less pronounced. The glass transition temperature of the acetonide functional materials is comparable to values previously reported for bis-MPA dendrimers.114,115

The hydroxyl functional dendronized polymers show a similar increase in glass transition temperature as the acetonide capped sample set but more pronounced. The change in polarity of the end-groups upon going from acetonide to hydroxyl functionality is reflected in the glass transition temperature. The hydroxyl functional materials have a Tg approximately 12 to 15 °C higher than the acetonide functional set.

In the case of the set of dendronized polymers capped with hexadecyl chains, no glass transition was detected (Figure 15). Instead these materials displayed crystallization (Tc) and melting (Tm) peaks (listed in Table 6). The values for Tm and Tc data are similar to data reported by Wang et al.116 for branched polyethyleneimines with hexadecyl side-chains and for bis-MPA based dendrimers with hexadecyl chains.114

Figure 15. DSC traces for the hexadecyl capped samples. Open symbols cooling, filled symbols heating. p-HEMA-G#2-Ac ( , ), p-HEMA-G#3-Ac ( ,▲), p-HEMA-G#4-Ac ( , ). The markers represent every 50th data point.


34

By integration of the melting peak and normalizing it to sample size, ∆Hm for the different samples was obtained. Since these dendronized polymers are symmetric, the molar ratio of end-groups to dendritic segments is essentially constant upon increasing the generation. Therefore, a change in ∆Hm upon increasing the size of the pendant dendrons should reflect a change in crystallization ability of the end-groups. In Table 6 it can be seen that ∆Hm decreases with increasing generation. This suggests that the crystallization ability of the end-groups is reduced when attached to larger dendrons. Flexible backbones allow for more efficient packing of side chains and promote crystallinity,116 but since it has been shown that the attachment of larger dendrons to the backbone of a polymer will reduce its flexibility,90 it is hypothesized that the reduced flexibility of the backbone results in a lowering of the ∆Hm. Table 6. Summary of DSC results for the dendronized poly(hydroxyl ethyl methacrylate).

Sample Tg [°C] Tc [°C] Tm [°C] ∆Hm [J/g]

p-HEMA-G#2-Ac 25.8 - - -

p-HEMA-G#3-Ac 26.5 - - -

p-HEMA-G#4-Ac 28.8 - - -

p-HEMA-G#2-OH 38.0 - - -

p-HEMA-G#3-OH 40.1 - - -

p-HEMA-G#4-OH 43.8 - - -

p-HEMA-G#2-C16 - 20.2 27.1 53.9

p-HEMA-G#3-C16 - 19.3 29.3 48.5

p-HEMA-G#4-C16 - 22.2 27.9 38.3


35

4.6.2 Differential Scanning Calorimetry – Dendronized Poly(norbornene) The glass transition temperature (Tg) of the dendronized poly(norbornenes) polymers were

determined from the second heating DSC run and taken as the middle point of the transition, and the results are summarized in Table 7. The Tg values for these polymers where in the same range as the acetonide functional dendronized poly(hydroxyl ethyl methacrylate), (~ 20-30 ºC). This indicates that bis-MPA based dendronized polymers are rather low Tg materials. As seen in Table 7, the Tg of the dendronized polymers decreases slightly with increasing generation, from a value of around 30 ºC for the first generation material to around 23 ºC for the fourth generation material. Since the Tg of the poly(hydroxyl ethyl methacrylate) samples, that all have the same DP, increases with generation, it is reasonable to assume that the decreased Tg observed for higher generations of the dendronized poly(norbornene) is related to the reduction in degree of polymerization (DP) of these materials. As suggested for other types of dendronized polymers, a lower chain length may reduce the fraction of less mobile polymer core, hence increasing the segmental mobility of the dendronized polymer even though the spatially demanding dendrons increases in size.113 Table 7. Summary of DSC results for the dendronized poly(norbornene). Sample DPa DPb Tg [ºC]

p-Nor-G#1 [9] 237 156 33.2

p-Nor-G#1 [13] 551 243 30.4

p-Nor-G#2 [10] 121 116 17.9

p-Nor-G#2 [14] 271 201 25.4

p-Nor-G#3 [11] 59 63 24.1

p-Nor-G#3 [15] 155 139 25.1

p-Nor-G#4 [12] 21 24 22.3

p-Nor-G#4 [16] 56 55 23.0

p-Nor-G#4 [17] 52 57 22.7 a SEC Mn conventional calibration, b SEC Mn Universal calibration. [X] Corresponding entries in Table 4.


36

4.6.3 Rheological Characterization - Dendronized Poly(hydroxyl ethyl methacrylate)

Dynamic mechanical measurements on dendronized polymers have been reported in the literature.47,81,117 The mechanical properties of these polymers are thought mainly depend on two characteristics, the backbone length and dendron size.47 In the case of dendronized polymers prepared by a combination of controlled polymerization techniques and the divergent ‘graft-to’ approach the materials obtained will have the same backbone length. This allows for a less complicated investigation of their generational and end-group dependent material properties to be conducted.

The set of dendronized polymers was studied by rheology. Figure 16 (left) displays the frequency dependence of the complex viscosity for the acetonide capped samples. As seen in the figure p-HEMA-G#2-Ac exhibits Newtonian behavior at low frequencies and shows a slight shear thinning behavior at higher frequencies. Upon increasing the size of pendant dendrons, the complex viscosity increases by approximately an order of magnitude at low frequencies and the shear thinning behavior starts at lower frequencies. In the case of p-HEMA-G#4-Ac, the complex viscosity at the lowest frequency tested increases by approximately 2.5 orders of magnitude and the sample is shear thinning over the whole frequency spectra tested. Dendronized polymers with isocyanate backbones have been reported having a similar initial Newtonian behavior that changes to shear thinning at higher frequencies.117

Figure 16. Left; Complex viscosity as function of frequency for dendronized polymers with acetonide end-groups. Data collected at 80 °C. p-HEMA-G#2-Ac ( ), p-HEMA-G#3-Ac ( ), p-HEMA-G#4-Ac ( ). Right; Complex viscosity as function of frequency for dendronized polymers with hydroxyl end-groups. Data collected at 80 °C. p-HEMA-G#2-OH ( ), p-HEMA-G#3-OH ( ), p-HEMA-G#4-OH ( ).

Figure 16 (right) depicts the rheological investigation of the hydroxyl functional samples.

These materials show the same frequency dependence of the complex viscosity as the acetonide functional materials. The difference being that the Newtonian behavior for the p-HEMA-G#2-OH and p-HEMA-G#3-OH extends for a shorter frequency range. The increase in complex viscosity as a function of generation is also similar to the acetonide materials.

The dendronized polymers capped with hexadecyl chains were investigated in the same manner as the previous sample set. However, the low viscosity of the materials at


37

temperatures above Tm required that the frequency sweeps were conducted at a lower temperature compared to the previous measurements. Figure 17 (left) depicts the complex viscosity as a function of frequency for the hexadecyl functional materials. The complex viscosity followed the same trend as the acetonide and hydroxyl functional materials. The complex viscosity at the lowest frequency tested increases for each generation and same the Newtonian to shear-thinning transition is observed.

Figure 17. Left; Complex viscosity as function of frequency for dendronized polymers with aliphatic hexadecyl end-groups. Data collected at 40 °C. p-HEMA-G#2-C16( ), p-HEMA-G#3-C16 ( ), p-HEMA-G#4-C16 ( ). Right; Complex viscosity as function of frequency for dendronized polymers of the fourth generation. p-HEMA-G#4-Ac ( ), p-HEMA-G#4-OH ( ), p-HEMA-G#4-C16 ( ).

It is proposed that the gradual change from Newtonian to shear thinning behavior upon

increasing size of the dendrons could be an effect of the backbone changing conformation from a random coil towards a more stretched rod-like conformation. This change in behavior is visible for all sample tested, suggesting that the end-groups of the dendronized polymers determines the level of the complex viscosity and the generation the behavior as a function of frequency (Figure 17 right). The hydroxyl functional materials have the highest complex viscosity of the series, most likely due to hydrogen bonding in the material. The hexadecyl capped samples were tested above the crystalline melting point of the material, which results in the samples having the lowest complex viscosity of the series. The acetonide capped dendronized polymers does not form hydrogen bonding and therefore the complex viscosity of these materials is lower than the hydroxyl functional materials. For each increase in generation of the dendronized polymers, the complex viscosity at the lowest frequency is increased. This increase is more pronounced when going form the third to fourth generation.


38

4.6.4 Rheological Characterization - Dendronized Poly(norbornene) The dendronized polynorbornenes were investigated by dynamic rheological

measurements performed in a similar manner as for the dendronized poly(hydroxyl ethyl methacrylate). The rheological measurements were conducted well above the glass transition of the corresponding materials, in a frequency range of 0.1-200 rad/s. The dynamic mechanical behaviour in the high and low frequency region for the dendronized polymers reflects the glassy (high ω) and liquid-like properties (low ω) of the material, and the behaviour in between these frequencies reflects the structure of the polymer.113 It would of course be interesting to investigate the viscoelastic properties of these materials in a higher frequency range, but the thermal sensitivity of acetonide protected dendritic structures above 130 ºC limits the use of temperature-frequency superposition method for these materials.115

Figure 18 (left) displays the frequency dependence of the storage modulus (G’) and loss modulus (G”) at 80 ºC for the p-Nor-G#1 polymers (entries 9, and 13 in Table 4). As seen in the figure, the dependence of the G’, G” with increasing DP is rather weak. For the p-Nor-G#2 material (entries 10, 14 in Table 4) in Figure 18 (right), a stronger dependence of the DP on the G’ G” is observed. The G’ and G” drops significantly more with decreasing frequency for the lower DP material and this material also displays one G’/G” crossover in the high frequency range. Typically, G’/G” crossover points is related to deformation rates that are in the same range as the segmental relaxation of a polymer. A similarly strong dependence of the DP can be observed in the case of the p-Nor-G#3 samples in Figure 19 (left) (entries 11 and 15 in Table 4), were the G’ and G” of the high DP material drops less than the low DP material. One can also observe that the crossover at the lower frequencies for the high DP material is shifted towards a higher frequency compared to the second generation material. The p-Nor-G#4 materials (entries 12 and 16 in Table 4) in Figure 19 (right) behave in a similar way, with a weak effect on the G’ and G” for the lower DP material, but without an observable crossover in the tested frequency range.

Figure 18. Left; Storage modulus G’ (filled symbols) and loss modulus G’’ (open symbols) as a function of frequency (ω) for (∆) p-Nor-G#1 [DP 237], (◊) p-Nor-G#1 [DP 551]. Right; Storage modulus G’ (filled symbols) and loss modulus G’’ (open symbols) as a function of frequency (ω) for (∆) p-Nor-G#2 [DP 121], (◊) p-Nor-G#2 [DP 271]. [X] Corresponding entry in Table 4.


39

Figure 19. Left; Storage modulus G’ (filled symbols) and loss modulus G’’ (open symbols) as a function of frequency (ω) for (∆) p-Nor-G#3 [DP 59], (◊) p-Nor-G#3 [DP 155]. Right; Storage modulus G’ (filled symbols) and loss modulus G’’ (open symbols) as a function of frequency (ω) for (∆) p-Nor-G#4 [DP 21], (◊) p-Nor-G#4 [DP 56]. [X] Corresponding entry in Table 4.

When comparing the G’ and G” in Figure 18 and 19, one observes a strong effect on the viscous (G’) and elastic (G”) contribution to the complex modulus when going from the first generation material to higher generations. Previous studies on low DP dendronized polymers have suggested the size of the pendant dendrons mainly affect the G’ part of the complex modulus,117 and as seen for the lower DP materials in Figure 18 and 19, a similar effect can be observed. However, in case of the higher DP polymers, the effect of dendron size on the viscous and elastic contributions is much stronger in the lower frequency range. The slopes of the G’ and G” are similar for the higher DP p-Nor-G#2, G#3, and G#4 materials indicating a similar relaxation behaviour but with the limiting values at low frequencies differing considerably more than for the low DP polymers.

Figure 20 depicts the frequency dependence of the complex viscosity at 80 ºC for the two sets of first to- fourth generation dendronized polymers, first set (entries 9, 10, 11, and 12 in Table 4), second set (entries 13, 14, 15, and 16 in Table 4). As seen in Figure 20 (left), p-Nor-G#1 is shear thinning in the whole frequency spectrum tested. When increasing the generation from one to two there is a pronounced drop in complex viscosity in the low frequency range and the material exhibit a Newtonian plateau after which it becomes shear thinning. Increasing the generation to three and four increases the plateau and the samples become shear thinning at higher frequencies. When comparing these materials with the second set of dendronized poly(norbornene) with higher DP, depicted in Figure 20 (right), a different rheological behaviour can be observed. The first generation sample shows the same complex viscosity as function of frequency behaviour, with similar limiting complex viscosity values. The Newtonian plateaus in the low frequency region observed for the second, third and fourth generation materials with lower DP in Figure 20 (left) are not as pronounced in Figure 20 right, and the limiting values of the complex viscosity at low frequencies follows the order p-Nor-G#1>G#2>G#3>G#4.

The observed differences in the rheological behaviour seen for the second, third and fourth generation materials in Figure 20 may be a result of chain entanglements, since the dendronized polymers in this study lacks groups capable of forming secondary bonds that would result in non-Newtonian flow behaviour. Jahromi et al. suggested that the average molecular weight between two neighbouring entanglements increases as the effective shielding of the backbone by the pendant dendrons increases with size.117 Hence, the low DP


40

p-Nor-G#2 sample depicted in Figure 20 (left) has too low DP in order to effectively entangle, whereas the higher DP p-Nor-G#2 material entangle. This conclusion is supported by the presence of a clear G’/G” crossover in the lower frequency range for the high DP p-Nor-G#2 sample in Figure 18 (right), indicating the formation of a physical network. The same can be seen for the p-Nor-G#3 samples. However, as seen in Figure 19 (right), the p-Nor-G#4 samples both lack a G’/G” crossover and their rheological behaviour is quite different.

Figure 20. Right; Complex viscosity (η*) as a function of frequency (ω) for the low molecular weight dendronized polymers (∆) p-Nor-G#1 [DP 237], (◊) p-Nor-G#2 [DP 121], (□) p-Nor-G#3 [DP 59], (○) p-Nor-G#4 [DP 21]. Left; Complex viscosity (η*) as a function of frequency (ω) for the high molecular weight dendronized polymers (∆) p-Nor-G#1 [DP 551], (◊) p-Nor-G#2 [DP 271], (□) p-Nor-G#3 [DP 155], (○) p-Nor-G#4 [DP 57]. [X] Corresponding entry in Table 4.


41

1H-NMR Diffusion and Relaxation studies (Papers III and VI)

4.6.5 Dendronized Poly(hydroxyl ethyl methacrylate) The dendronized polymers capped with acetonide end-groups and hydroxyl groups were

also characterized by 1H longitudinal relaxation and pulsed field-gradient spin-echo (PGSE) NMR, with results summarized in Table 8. Both relaxation and PGSE NMR’s have previously proven useful for the characterization of many different polymer systems including bis-MPA based dendrimers.96 The data in were first fitted to a globular model using the Debye-Stokes-Einstein relationship (Eq 1), however the result obtained suggest that the geometry of these polymers in solution is not globular. Instead, a better fit was obtained by Kirkwood’s model for translational diffusion (D) of rod-like objects118,119

[ln( / ) ]3

Bk T L bDL

γπη

−= , (2)

where kB is the Boltzmann constant, T the absolute temperature, η the viscosity of the

solvent (DSMO-d6, η (20 °C) = 2.14 cP, D2O, η (20 °C) = 1.2 cP), γ ≈ 0.3, while L and b are the rod length and diameter, respectively. In the same model, the rotational diffusion coefficient (Drot) is

3

3 [ln( / )Brot

k T L bDL

]γπη

−= . (3)

Modelling the polymer as a prolate ellipsoid and calculating its translational and rotational

diffusion within the Perrin model also resulted in a better fit.120,121 The results obtained by either the Kirkwood or Perrin models suggest that these polymers adopt a more rod-like conformation in solution as opposed to a random coil. Looking at the hydroxyl capped polymers in Table 8 it can be seen that the diffusion coefficients of the polymers are significantly lower in DMSO-d6 than in D2O. Table 8. 1H-NMR self-diffusion and longitudinal relaxation data for the acetonide and hydroxyl functional dendronized poly(hydroxyl ethyl methacrylate) dissolved in DMSO-d6 or D2O.

Sample D [10-11m2/s] DMSO-d6

D [10-11m2/s] D2O

b [Å] a DMSO-d6

b [Å] a D2O

p-HEMA-G#2-Ac 4.1 - 10 - p-HEMA-G#3-Ac 3.2 - 16 - p-HEMA-G#4-Ac 2.9 - 18 - p-HEMA-G#1-OH 4.5 9.9 8 5 p-HEMA-G#2-OH 4.3 9.0 9 6 p-HEMA-G#3-OH 3.8 7.9 11 8 p-HEMA-G#4-OH 3.2 7.1 15 12

a Diameter b of the rod-like polymer entity of 100 Å assumed length, obtained from the diffusion data evaluated within the Kirkwood model.

The rod diameter increases with the dendron generation both in water and in DMSO and the polymers have larger diameters in DMSO than in water, which indicates a more swollen conformation in DMSO. Compared to the acetonide functional polymers of the same generation in DMSO, the diameters of the hydroxyl functional polymers are somewhat


42

smaller. This may arise either from the larger size of the acetonide functionality compared with hydroxyls of the same generation or due to higher solubility of the acetonide groups in DMSO, leading to a more swollen conformation. A more elaborate discussion about the results is given in papers 3 and 6.


43

4.7 Birefringent Fibers Dendronized Poly(norbornene) (Paper IV) Percec et al.122 and Pakula et al.81 have prepared fibers form dendronized polymers

bearing pendant self-assembling dendrons that introduce order in bulk state. Depending on the type of self-assembling dendrons, a range of shapes of the corresponding crystalline structures have been obtained. As a serendipius discovery it was found that the fourth generation dendronized poly(norbornene) (p-Nor-G#4, entry 17 in Table 4) formed long (> 40 cm) fibers when the parallel plate setup was retracted at 80 °C, during the rheological measurements. This effect was very surprising since the dendronized poly(norbornene)s are low Tg amorphous materials without any structural moieties that can induce self assembly. When analyzing the fiber by DSC, only a glass transition was observed.

Figure 21 shows the optical microscopy image taken of one of these fibers using crossed polarizers and a λ-plate. The fibre was simply drawn directly from a melt of the fourth generation sample and as seen in Figure 21, the fibre is birefringent with a higher refractive index perpendicular to the fiber axis. Spin-cast films of the same material did not show any evidence of birefringence, and the lower generation materials could not be stretched into long thin fibers (> 40 cm) without breaking.

Figure 21. Polarized optical microcopy image of a fiber from p-Nor-G#4 [17]. Image taken with crossed polarizers, 16 times magnification, and λ-plate, fiber rotated 45 ° left from the director. [X] Corresponding entry in Table 4.

The fibers were also investigated by polarized attenuated total reflection Fourier transform infrared spectroscopy (polarized ATR-FTIR) and X-ray diffraction measurements. Polarized ATR-FTIR is a useful technique of investigating macromolecular orientation since the orientation of selected bands in the polymer can be assessed.123,124 For example, given that the induced orientation mainly is due rearrangements of the backbones, the vibrations in the fingerprint region of the IR spectra specifically related to the backbone should yield valuable information. The cis (~730 cm-1) and trans (960 cm-1) out of plane bending vibrations for the HC=CH bond in the polymer backbone are examples of vibrations related to the polymer backbone.125 Figure 22 displays the polarized IR spectrum of this region for the fiber (top) and the unoriented material (bottom) were the dashed line represent the absorption parallel (A║) to the director (placed in the fiber direction), and the solid line the absorption perpendicular (A┴) to the fiber. When constructing the spectra, the curves were normalized with respect to the absorption of the carbonyl group. This group was chosen because it can be assumed that the esters in this highly branched polyester architecture will have no preferred orientation. The dichroic ratio (R) is defined as R = A║/A┴, and can be used to calculate the Hermans orientation function f, given that the dichroic ratio (R0) for a perfect uniaxial


44

orientation is known.126 Since R0 is difficult to determine experimentally, the dichroic ratio for the bulk material and the fiber at the cis and trans vibrations was simply compared. The cis vibration results in a dichroic ratio for the fiber, RF-cis ~ 1.24 and RB-cis ~ 1.09 indicating that the cis portion of the backbone is more oriented in the fiber direction. Looking at the trans vibration one can see a weaker increase of the dichroic ratio between the unoriented material RB-trans ~ 0.86 and the fiber RF-trans ~ 0.94.

Figure 22. Polarized attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra of a fiber (top) from p-Nor-G#4 [17], unoriented material (bottom). Dashed line absorption parallel to the fiber direction, solid line absorption perpendicular. [X] Corresponding entry in Table 4.

The birefringent fibers were also analyzed with X-ray diffraction measurements, and the diffractograms of the fiber oriented parallel and perpendicular to the source of irradiation and the unoriented material is presented in Figure 23. For both the orientation directions of fiber and the bulk material, intense peaks corresponding to distances of ~43 Å, ~22 Å, ~14.5 Å were found, with less intense peaks at ~11 Å, 9 Å and a halo around 5 Å. As seen in Figure 23 the sharp reflections are of the same magnitude for all samples, with a more pronounced halo for the unoriented material being the only difference observed, suggesting that the amorphous content of the fiber is lower.

Figure 23. XRD diffractograms of a fiber from p-Nor-G#4 [17], where the red line is the fiber oriented perpendicular to the source of irradiation, blue line parallel to the irradiation, black line bulk material. [X] Corresponding entry in Table 4.

Conclusion

5 Conclusions By attaching a spacer between the dendron and the porphyrin ring, two sets of dendritic

porphyrins (up to the fifth generation) could be grown. Without this aliphatic pacer, divergently grown dendritic porphyrins were not attainable due to the hydrolytical instability of the phenolic ester bond. Dendron decorated porphyrins may also be used for the non-covalent construction of dendronized polymers. In comparison to the Fréchet-type benzyl ether dendritic porphyrins of the same generation, the bis-MPA based porphyrins have smaller hydrodynamic volume in THF.

Dendron bearing methacrylates could be synthesized on a large scale by utilizing the acetonide protected anhydride of bis-MPA as generic building block. The kinetic investigation of their ATRP polymerization revealed that the ligand N-propyl-2-pyridylmethamine resulted in polymers with the lowest polydispersity. Combining these polymers with the divergent ‘graft-to’ method proved to be a versatile route to obtaining well-defined dendronized polymers with tailored end-group functionalities emanating from the same backbone. Overall, ATRP of dendron bearing macromonomers was found to be the best technique for preparing dendronized polymers with moderate molecular weights and low PDI’s.

First to fourth generation dendron bearing norbornenes could be polymerized by ROMP utilizing Grubbs´ first and second generation catalysts at room temperature. The polymerization with the first generation catalyst resulted in polymers with considerably lower polydispersities than the materials obtained with the second generation catalyst but more work is necessary in order to find the optimum reaction conditions for these polymerizations.

The copper(I) catalyzed “Click” reaction between divergently grown azido functional dendrons and propargyl acrylate, proved to be a high yielding and convenient synthetic route to dendron bearing macromonomers. The acrylate functional monomers could be polymerized to dendronized triblock copolymers via RAFT, using a PMMA based macroCTA and AIBN as radical generator.

DSC analysis of the dendronized poly(hydroxyl ethyl methacrylate) revealed that the Tg increases with increasing size of the pendant dendrons, and the functionality of the end-groups had a profound influence on the level of the glass transition. Both the acetonide functional poly(hydroxyl ethyl methacrylate)s and poly(norbornene)s were found to have similar Tg’s suggesting that the functionality of the dendronized polymer has a strong influence on the final Tg of these polymers.

The rheological investigation of the dendronized poly(hydroxyl ethyl methacrylate) showed that the level of the complex viscosity increased for each generation of the dendron. Independently of the functionality of the dendronized polymer, the p-HEMA-G#2 and G#3 generation materials are Newtonian up to a limit in frequency after which they become shear thinning. The G#4 generation samples showed shear thinning behavior in the whole frequency range tested.

A pronounced effect of degree of polymerization on the complex viscosity as a function of frequency was also found for the poly(norbornene) materials. The second, third and fourth generation materials with lower DP’s displayed Newtonian behaviour from the lowest frequencies up to a certain limit after which they became shear tinning. The sample set of higher DP displayed shear thinning at much lower frequencies for all generations. The different complex viscosity behaviour of the poly(hydroxyl ethyl methacrylate)s and the poly(norbornene)s may be a result of the larger distances between the dendrons in the poly(norbornene) backbone compared to the vinyl backbone in the HEMA based materials.

45

Future Work

46

6 Future Work Preparing dendronized polymers via controlled polymerization techniques is challenging

combination of organic- and polymer chemistry. Combining a controlled polymerization technique with the “graft-to” methodology offers the potential of creating materials having the same backbone length. This in turn simplifies the analysis of the structure-property relationship of these materials but has the drawback of being time consuming and possibly very difficult for high molar mass polymers.

Atom transfer radical polymerization of dendron bearing macromonomers is maybe the best technique for preparing dendronized polymers with moderate molecular weights and low PDI’s. Therefore, it would be interesting to further elaborate on the ATRP polymerization of more complex dendron bearing macromonomers.

Ring-opening metathesis polymerization of dendron bearing norbornenes is a promising route to high molecular weight dendronized polymers. In order to overcome the problems with decreasing molecular weights for the higher generation norbornenes encountered in this work, enantiomer pure and symmetric norbornenes should be used, and maybe also evaluated with the third generation Grubbs´ catalyst.

In order to prepare dendronized triblock copolymer with higher degree of polymerization of the dendritic blocks, a more elaborated investigation must be conducted. Tailoring of the polymerizable group and tests with other types of chain transfer agents might solve the difficulties in obtaining higher molecular weight polymers.

Preparation of conjugated dendronized polymers, where the dendrons serve as “bumpers” preventing aggregation and loss of performance is another area of interest, were the high solubility of bis-MPA based dendronized polymers can be useful.

Acknowledgements

7 Acknowledgements First of all I would like to thank my excellent supervisor Prof. Anders Hult for accepting

me as a PhD student in his group. I would also like to thank him for his support, scientific guidance, and creative ideas during these years.

Prof. Eva Malmström is gratefully acknowledged for her newer ending enthusiasm and her ability to always finding time for scientific discussions, guidance, and help with my papers.

Prof. Mats Johansson, is acknowledged for both early morning and late night discussions about both science and other topics as well for all help with measurements.

Financial support by The Swedish Research Council under grants 2002-5719, and 2005-6169, is acknowledged with appreciation. This work was also supported by “Photonics in defense applications”-a program run jointly by the Swedish Defence Research Agency (FOI) and Defence Material Administration (FMV).

Travel grants from Stiftelsen Svensk Färg och Lackforskning, Knut and Alice Wallenberg foundation, and The Royal Swedish Academy of Sciences is also acknowledged.

Prof. Mikael Lindgren is acknowledged for his help and measurements making paper I and future papers possible.

Prof. Ulf Gedde is acknowledged for being a good teacher and for his scientific guidance and valuable discussions regarding polymer physics.

Prof. Hiekki Tenhu and Dr. Sami Hietala are acknowledged for the help with the dn/dc measurements and their work on making paper 6.

Ass. Prof. István Furó is acknowledged for doing the diffusion measurements and the help with the corresponding papers.

Dr Michel Malkoch is acknowledged for being a good friend and for sharing his knowledge of useful chemistry.

Dr Robert Vestberg is acknowledged for being very good friend and an excellent mentor in golf and chemistry.

Dr Ronnie Palmgren is acknowledged for his help with the SEC-MALLS measurements. Inger Lord is thanked for all the help with all practical arrangements and especially for

keeping copies of everything of importance. Prof. Nikos Hadjichristidis, Ass. Prof. Iartou Hermolaos, Ass. Prof Stergios Pispas, Ass.

Prof Marinos Pitsikalis is thanked for the opportunity of visiting their lab and for the help with the arrangements concerning my stay in Athens.

Prof. Ann Christine Albertsson, Prof. Sigbritt Karlsson, Prof. Mikael Hedenqvist, and Prof. Bengt Stenberg are acknowledged for their hard work making this department a creative and good place to work.

The administrative personnel, Margareta Andersson, Ove Källberg, Barbara Karan, Abha Karam, Viktoria Bylund, Emma Hareide, Maria Qvist, Maria Andersz, are thanked for their help with paper work, practical matters, and everything else necessary for things to run smoothly.

The present members of “Ytgruppen” is acknowledged. Daniel N for being a very good friend and for his input on paper 4. Pelle for his help with the MALDI and for being the next flash king in the group. Dr. “γ-string” George for all his input and help. Emma for being the best room mate of all my room mates. Robert for having a positive approach to everything and for your crazy family stories. Hanna “chairperson of Stefan and Krister fanclub” for ordering all my solvents and chemicals. Josefina for your help on ATRP. Linda for always presenting an opposite opinion. Kattis for helping me with the rheometer. Daniel S for making late night coffee. Neil for teaching me all the good English “English” words. Camilla for

47

Acknowledgements

taking over the SEC responsibilities. Magnus “lab in a bag” for his help with NMR interpretation.

The former PhD students during the years for their help and input. Hasse for being the least PC guy I know, Peter for being a good friend and for finding everything interesting -always. Björn “the stockbroker” for always presenting a perspective on things. Janis for being a good friend and an excellent instructor in golf.

The rest of the PhD students at the department are acknowledged for supplying the atmosphere that makes this apartment a good place to work.

My friends in the “real” world are acknowledged, none mentioned none forgotten. My family is acknowledged for their support, especially Mamma för all ditt stöd. Finally my “growing” family, Veronica, I love you. Take good care of “pyret” until she/he

arrives.

48

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53

Appendix

54

9 Appendix I. Structures of the synthesized monomers and polymers

Appendix

N

N

N

N

OO

OO

OH

HO

HO

OH

N

N

N

N

OO

OO

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

N

N

N

N

OO

OO

O

O

O

O

O

OH

OHO

HO

HO

O

OH

OH

O

HO

HO

HO-prop-TPPH2

Acetide-prop-G#1-TPPH2 HO-prop-G#1-TPPH2

55

Appendix

O

O

O

O O

O

O

OO

N

N

N

N

OO

OO

O

O

O

O

O

O

O

O O

O

O

OO

O

O

O

OO

O

O

O O

O

O

O

OO

O

O

O O

O

O

O

O OH

OH

O

OHOH

N

N

N

N

OO

OO

O

O

O

O

O

O

O

O OH

OH

O

OHOH

O

O

O

OHO

HO

O

HO HO

O

O

O

OHO

HO

O

HO HOAcetonide-prop-G#2-TPPH2 HO-prop-G#2-TPPH2

56

Appendix

N

N

N

N

OO

OO

O

O

O

O

O

O

O O

O

OO

O

O O

O

O

OO O

OO

O

OO

OO

O

OO

O

OO

O

OO

O

O

O OO

OO

O

OO

O

O

O

OO

O

OO

O

OO

O

O

O OO

OO

O

OO

OO

O

O O

O

OO

O

O O

O

O

OO O

OO

O

OO

O

N

N

N

N

OO

OO

O

O

O

O

O

O

O O

O

OOH

OH

O OH

OH

O

OO O

OHOH

O

HOHO

OO

O

OO

O

OHO

HO

OHO

HO

O

O OO

HOHO

O

OHOH

O

O

O

OO

O

OHO

HO

OHO

HO

O

O OO

HOHO

O

OHOH

OO

O

O O

O

OOH

OH

O OH

OH

O

OO O

OHOH

O

HOHO

O

Acetonide-prop-G#3-TPPH2 HO-prop-G#3-TPPH2

57

Appendix

N

N

N

N

OO

OO

O

O

O

O

O

O

O O

O

O

O

O

OO

O

O O

O

O

O

O

OO

O

OO

OO

OO

O

O

O

O

OO

O

OO

O

OO

O

OO

O

O O

OO

O

OO

O

O

O

O

OO

O

OO

O

O

O

O

OO

O

OO

OO

O O

O

O

O

O

OO

O

OO

O

OO

O

OO

O

OO

O

O

O

OO

O

O

O

O

OO

O

OO

O

O

O

O

OO

O

OO

OO

O O

O

O

O

O

OO

O

OO

O

OO

O

OO

O

OO

OO

O

O O

O

O

O

O

OO

O

O O

O

O

O

O

O O

O

OO

OO

OO

O

O

O

O

OO

O

OO

O

OO

O

OO

O

O O

O

N

N

N

N

OO

OO

O

O

O

O

O

O

O O

O

O

OH

OH

OO

O

O O

O

O

OH

OH

OOH

OH

OOH

OHO

OO

O

OH

OH

O

OO

O

OO

O

OHOH

O

HOHO

O

OH OH

OO

O

OO

O

O

HO

HO

OO

O

OO

O

O

HO

HO

OHO

HO

OHO

HOO

O O

O

HO

HO

O

OO

O

OO

O

HOHO

O

OHOH

O

HOHO

O

O

O

OO

O

O

HO

HO

OO

O

OO

O

O

HO

HO

OHO

HO

OHO

HOO

O O

O

HO

HO

O

OO

O

OO

O

HOHO

O

OHOH

O

HOHO

OO

O

O O

O

O

OH

OH

OO

O

O O

O

O

OH

OH

O OH

OH

OOH

OHO

OO

O

OH

OH

O

OO

O

OO

O

OHOH

O

HOHO

O

OH OH

O

Acetonide-prop-G#4-TPPH2 HO-prop-G#4-TPPH2

58

Appendix

OO

O O

O

O

OO

OO

O O

O O

O

O

OO

OO

OO

O

O

O

OO

O O

OO

O

OOO

OO

O

O

O

O

O

O

OO

O

OO

OO

O

O

OO

O O

OO

OO

O

O

OO

OO

O O

O

O

O

O O

OO

OOO

O OO

O O

O

O

O

O

OO

OO

O

OO

O

OO

OO

O

OO

O

OO

O

O

OO

OO

O

O

O

O

OO

O

OO

O

O

OO

O

OO

O

OO

O

OO

OO

OOO

OOO

O

O

OO

O

O

O

O

OO

O

O

OO

OO

O

O

O

O

OO

O

OO

O

O

OO

O

OO

O

OO

OO

O

OO

OOO

OOO

O

O

O O

OO

O

OO

O

OO

O

O

O O

O O

O

O

O

O

OO

O

OO

O

O

OO

O

O O

O

O O

OO

O

OO

OO O

OO O

O

O

OO

O

OO

O

OO

O

O

O O

O O

O

O

O

O

OO

O

OO

O

O

OO

O

O O

O

O O

OO

O

OO

OO O

OO O

O

O

O

O

NH N

HNNO

OO

OO

O

O

OO

O O

OO

OO

O

O

OO

OO

OO

O

O

O

O O

OO

OO

O

O OO

OO

O

O

O

O

OO

OO

O

O O

O O

O

O

OO

OO

O O

O O

O

O

OO

OO

OO

O

O

O

OO

O O

OO O

OOO

OO

O

O

O

O

O

O

OO

O

OO

Acetonide-prop-G#5-TPPH2

59

Appendix

O

OBr

OO

OO

O O

n O

OBr

OO

OO

O O

O

OO

O

OO

m O

OBr

OO

m O

OBr

OO

m

OO

O O

O

OO

O

O O

O

O O

O

O

O

O

OO

O

O

OO

OO

O

OO

O

OO

O

OO

O

O

O

O

OO

O

O

O O

OO

OO

O O

O

OO

O

O O

O

O

O

O

OO

O

OO

O

O

O

O

OBr

OO

OO

OH OH

n O

OBr

OO

OO

O O

O

OHOH

O

HOHO

m O

OBr

OO

m

OO

O O

O

OO

O

OH OH

O

OH

OH

O

OO

O

HOHO

O

HO

HO

O

OBr

OO

m

OO

O O

O

OO

O

OH OH

O

O O

O

O

O

O

OHOH

O

OH

OHO

OHOH

O

OO

O

OHOH

O

OO

O

O

O

O

HOHO

O

HO

HO O

HOHO

p-HEMA-G#1-OH

p-HEMA-G#2-OH

p-HEMA-G#3-OH

p-HEMA-G#4-OH

p-HEMA-G#1-Ac

p-HEMA-G#2-Ac

p-HEMA-G#3-Ac

p-HEMA-G#4-Ac

60

Appendix

O

OBr

OO

OO

O O

O

OO

O

OO

m

O

OBr

OO

m

OO

O O

O

OO

O

O O

O

O

O

O

OO

O

OO

O

O

O

O

OBr

OO

m

OO

O O

O

OO

O

O O

O

O O

O

O

O

O

OO

O

O

OO

OO

O

OO

O

OO

O

OO

O

O

O

O

OO

O

O

O O

OO

O

O O

O

O

OOOO

O

O

O

O

O

O

OO

O

O

O

O

O

OO

O OO O

p-HEMA-G#2-Acetate

p-HEMA-G#3-Acetate

p-HEMA-G#4-Acetate

61

Appendix

O

OBr

OO

OO

O O

O

OO

O

OO

m

O

OBr

OO

m

OO

O O

O

OO

O

O O

O

O

O

O

OO

O

OO

O

O

O

O

OBr

OO

m

OO

O O

O

OO

O

O O

O

O O

O

O

O

O

OO

O

O

OO

OO

O

OO

O

OO

O

OO

O

O

O

O

OO

O

O

O O

OO

O

C15OC15 O C15

O

C15

O

C15

OC15

O

C15O

C15

OC15

O

C15

O

C15

OC15

O

C15 O

C15 O

C15O

C15O

C15

O

C15

O

C15O

C15O

C15O

C15O

C15

O

C15

OC15

OC15

OC15

OC15

p-HEMA-G#2-C16

p-HEMA-G#3-C16

p-HEMA-G#4-C16

62

Appendix

OO

OO

O

OO

O

OO

OO

OO

OO

O O

O

OO

O

O O

O

O O

O

O

O

O

OO

O

O

OO

OO

O

OO

O

OO

O

OO

O

O

O

O

OO

O

O

O O

OO

OO

O O

O

OO

O

O O

O

O

O

O

OO

O

OO

O

O

O

OO

OO

O

HOHO

O

OHOH

OO

OHOH

OO

O O

O

OO

O

OH OH

O

OH

OH

O

OO

O

HOHO

O

HO

HO

Nor-G#1-Ac

Nor-G#2-Ac

Nor-G#3-Ac

Nor-G#4-Ac

Nor-G#1-OH

Nor-G#2-OH

Nor-G#3-OH

63

Appendix

OO

OO

O

OO

O

OO

OO

OO

OO

O O

O

OO

O

O O

O

O O

O

O

O

O

OO

O

O

OO

OO

O

OO

O

OO

O

OO

O

O

O

O

OO

O

O

O O

OO

OO

O O

O

OO

O

O O

O

O

O

O

OO

O

OO

O

O

O

n n n n

p-Nor-G#1

p-Nor-G#2

p-Nor-G#3

p-Nor-G#4

64

Appendix

NN

N

OO

OO

O

OO

O

OO

OO

NN

N

OO

OO

OO

NN

N

OO

OO

O O

O

OO

O

O O

O

O O

O

O

O

O

OO

O

O

OO

OO

O

OO

O

OO

O

OO

O

O

O

O

OO

O

O

O O

OO

NN

N

OO

OO

O O

O

OO

O

O O

O

O

O

O

OO

O

OO

O

O

O

65

Appendix

NN

N

OO

OO

O

OO

O

OO

OO

OOO

OO

S

S m n

2

NN

N

OO

OO

OO

OOO

OO

S

S m n

2

NN

N

OO

OOO

OO

S

S m n

2

OO

O O

O

OO

O

O O

O

O O

O

O

O

O

OO

O

O

OO

OO

O

OO

O

OO

O

OO

O

O

O

O

OO

O

O

O O

OO

NN

N

OO

OOO

OO

S

S m n

2

OO

O O

O

OO

O

O O

O

O

O

O

OO

O

OO

O

O

O

66

dendrimers and dendronized polymers - synthesis and - diva

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