emulsion polymerization (2)

Polymer SynthesisCHEM 421

Emulsion Polymerization (2)

• External variable (surfactant concentration) used to increase BOTH molecular weight as well as rate of polymerization

• Colloidal system easy to control

– Thermal, viscosity issues

• Reaction mixture in form of final product for coatings

• Reaction product needs to be isolated from aqueous latex for many applications like rubber, elastomers, PVC, fluoropolymers, etc


Variables and Other Characteristics

• Redox Initiators– Hydrogen Peroxide w/ Ferrous Ion

• Surfactant-Free Emulsion Polymerization– Initiator fragment affords amphiphilic character

• Phase transfer catalysis (cyclodextran)• Microemulsion, Miniemulsion • Inverse emulsions• Core-Shell Particles• pH Control: Hollow Particles


Various Emulsions

• Emulsion Polymerization (macro)– Classic aqueous system

– Particles range from 50-500 nm

• Microemulsion Polymerization– Optically clear, smaller particles

– No droplets, just micelles

• Miniemulsion Polymerization– Between macro and micro systems, monomer

droplets smaller than in macro systems


Inverse Emulsion Polymerization

• Standard emulsion polymerization uses water as the continuous phase, or oil-in-water (O/W)

• Inverse Emulsions use:

– Oil as the continuous phase, or water-in-oil (W/O)

– Hydrophilic monomer (or aqueous solution of monomer) dispersed in oil, i.e. xylene/hexane

» Like Acrylamide

– Oil Soluble Initiator

– Surfactant


Surfactants

H2O

Oil

Surfactant Assemblies - Rich Morphologies

cationicsurfactant

anionicsurfactant

R

V

M

Vesicles

Rod-like Micelles

Micelles

Multi

V + L a

Multiphase Region

Vesicles and Lamellar Phase

5% SDBS

Water

V-

5% CTAT

V V

M

1% 1%

2% 2%

3% 3%

4% 4%RMulti

1% 2% 3% 4%

V+La

Inner Membrane

Outer Membrane

OP OOON

Inner Membrane

Outer Membrane

OP OOON

Controlled Radical Polymerization in Microemulsion

M M

M

Monomer-Swollen Micelles

Polymer Particle

Microemulsion Nanoparticles

Monomer Diffusion

M

M

M

P•PM•M

0 30 60 90 120 150 1800.0

0.2

0.4

0.6

0.8

1.0

[1]/[V50]=0 (RC1 data) [1]/[V50]=1.5 [1]/[V50]=2.25 [1]/[V50]=3.0 [1]/[V50]=4.5 [1]/[V50]=6.0

Con

vers

ion

(f)

Time (mins)

4 8 12 16

RI

Res

pons

e

Elution Time (mins)

[1]/[V50]=3.0 5.1% conversion Mn=2850, Mw/Mn=1.55 31.4% conversion Mn=6090, Mw/Mn=1.39 52.5% conversion Mn=9500, Mw/Mn=1.29 77.1% conversion Mn=12300, Mw/Mn=1.31 90.5% conversion Mn=16800, Mw/Mn=1.24

Liu, S. Y.; Kaler, E. W. et al. Macromolecules 2006, 39, 4345


Design of Polymeric Nanogelsfor DNA Delivery

Release of DNADiffusion Pathway

Research Objectives:

1. Design nanogels < 200 nm in diameter using inverse micro-emulsion techniques with excellent solution stability (w/o toxic solvents!)

2. Control release profile of DNA by selection of monomer and crosslinker composition and concentration

3. Attach targeting ligands to surface of nanogels

McAllister, K.; Sazani, P.; Adam, M.; Cho, M.; Rubinstein, M.; Samulski, R. J.; DeSimone*, J. M. J. Am. Chem. Soc. 2002, 15198-15207


Microemulsion Polymerizationand Isolation of Nanogels

Step 1:Form

microemulsion

Step 2:Polymerize

microemulsion

Step 3:Extract and

purify nanogels

Addition of Initiator to

oil phase andfree radical

polymerization

Removal ofheptane and

surfactantby extraction and dialysis


Designing Polymeric Nanogels

NanogelsMonomers

PEGdiacrylate n=8

2-Hydroxyethylacrylate

2-Acryloxytrimethyl-ammonium chloride

Increasing Crosslinker

Incr

easi

ng C

harg

e+

+

+

++

+

+

++

+

+

++

+

+

+

++

+

++

+

+

++

+++

+

++ + + +

+

++

+

++

+

++

++ +

++

OO

O

O

O

n

OHO

O

NO

O CH3 Cl -

CH3

CH3+


Dynamic Light Scattering of Microemulsion Before and After Polymerization

Dia

met

er (n

m)

Crosslinker Concentration (wt %)

0

20

40

60

80

100

0 10 20 30 40 50 60

= 0% Cationic Monomer



Before Polymerization

After Polymerization

AfterBefore


Cross-linked Particles Adsorbed to Surface

Low Crosslinking

Particles Flatten and Spread

High Crosslinking

Particles Maintain Shape


TEM Images of Nanogels

3% Crosslinker 12% Crosslinker 50% Crosslinker

0% C

harg

e12

% C

harg

e

66K Magnification Samples Stained with 1% PTA


% HeLa Cells Living After 40 Hour Exposure to Nanogels

0

20

40

60

80

100%

HeL

a Ce

lls L

ivin

g

Non

-ioni

c

Catio

nic

(12%

)

Catio

nic

(25%

)

Blan

k

Poly

lysi

ne


Release of Dye Molecules from Non-ionic Nanogels

Dialysis for 24 hoursat 37°C and at 4°C

Initial FluorescenceIntensity in Bag

Final FluorescenceIntensity in Bag

37°C = 100% 4° C = 100%

37°C = 4% 4° C = 8%


In Vitro Efficacy:Nanogel Uptake by HeLa Cells

Add Nanogels Wash Cells

HeLa Cells Cells + Nanogels Nanogels Bound to Cells


HeLa Cells Exposed to Nanogels

0% Charge 12% Charge 25% Charge

HeLa Cells Viewed at 400 x Magnification

After 24 h exposure to nanogels (12% cross-linker) and PBS wash


Confocal Microscopy of HeLa Cells Exposed to Rhodamine-Labeled Nanogels

0% Charge 12% Charge 25% Charge

3% C

ross

linke

r12

% C

ross

linke

r

Polymer SynthesisCHEM 421Future Directions

• Determine maximum DNA length which does not induce aggregation

• Evaluate in vitro delivery of DNA with nanogel/DNA complexes

• Extend to hydrolytically degradable matrices, targeting ligands, diffusion barriers

• Extend to peptides, pharmaceuticals, vaccines

Murthy N et al. PNAS 2003;100:4995-5000

Miniemulsion Polymerization for Dually-Triggered Degradable Nanogels

Li, Z. C, et al. et al. J. Controlled Release 2011, 152, 57


Core-shell Polymer Particles

General Practical Uses:• impact modification (soft core, hard shell) • providing chemical reactivity to latex particles • enhancement of adhesion properties (hard core, soft shell)• controlled-release drug delivery (water-soluble core)• prevent colors from showing through (hollow core)

Morphology:is determined by thermodynamic control (lowest surface free energy) and kinetic control. The second polymer doesn’t necessarily form the shell!

shell

core


Possible Morphologies

1st-stage polymer2nd-stage polymer

MicrodomainsA B

Raspberry SandwichA B

Kinetically Trapped Morphologies

Core-shell Inverted core-shell Half-Moon A Half-moon B

Thermodynamically Stable Morphologies


Hollow Particles & Ropaque™

Hollow particles in: paints, sunscreens, inks, cosmetics, fluorescent coatings, forgery- or counterfeiting-proof coated paper, paper products, etc.

•Hollow polymer particles industrially important•Can replace use of TiO2

•Ropaque™ made by Rohm & Haas

Kowalski, A.; Vogel, M. U.S. Patent 4,469,825.Blankenship, R.M.; Finch, W.C.; Mlynar, L.; Schultz, B.J. U.S. Patent 6,139,961.

microvoid

Raise pH Lower pH

CH3

OOH

O

CH3

OCH3

O

CH3

OCH3

O


Hollow Particle Micrographs

J. Poly. Sci. A: Polym. Chem., 2001, 39, 1435 Colloid Polym. Sci. 1999, 277, 252.

PMMA particles via W/O/W emulsion polymerization

Core-shell hollow particlesusing methacrylic acid

Emulsion Polymerization for Dye-Labeled Nanoparticles

Zhu, M. Q.; Li, A. D. Q. et al. J. Am. Chem. Soc. 2006, 128, 4303

PGMA macroCTA as a Steric Stabiliser for the Aqueous Dispersion Polymerisation of HPMA

Targeting a longer core-forming block relative to the stabiliser blockshould lead to progressively larger sterically-stabilised nanolatexes?

PGMA65

RAFT CTAHPMA

Y. T. Li and S. P. Armes, Angewandte Chem., 2010, 49, 4042

90 nm PGMA65-PHPMA200 latex 105 nm PGMA65-PHPMA300 latex

SEM images confirm spherical, near-monodisperse latexes

Scanning Electron Microscopy StudiesY. T. Li and S. P. Armes, Angewandte Chem., 2010, 49, 4042

PGMA65-PHPMA50 PGMA65-PHPMA70 PGMA65-PHPMA100

Dh = 29 nm Dh = 40 nm Dh = 58 nm

Scale bar: 100 nm

Negative staining using uranyl formate:Prof. S. Sugihara and Dr. A. Blanazs

Transmission Electron Microscopy StudiesY. T. Li and S. P. Armes, Angewandte Chem., 2010, 49, 4042

200 nm 200 nm 200 nm

DMF GPC Studies of PGMA-PHPMA Block Copolymers

A. Blanazs, S. P. Armes, A. J. Ryan et al., J. Am. Chem. Soc. 2011, ASAP

Aldrich-sourced HPMA has only 0.10 mol % dimethacrylate impurity

Best result: Mw/Mn < 1.20 for G47-H1000 at 99 % conv. (within 2 h at 70oC) !

So excellent control over MWD and good CTA blocking efficiencies….

A. Blanazs, S. P. Armes,

J. Madsen, A. J. Ryan

and G. Battaglia

JACS, 2011, ASAP

Scale bars: 200 nm

75 min = 62 %, DP 123

77.5 min = 68 %, DP 131

84 mins = 75 %, DP 150

225 mins = 100 % DP 200

90 mins = 82 %, DP 164

65 min = 46 %, DP 92

87 mins = 78 % DP 156

More In Situ Studies: PGMA47-PHPMAx

emulsion polymerization (2)

Documents

dna diffusion

control samples of dna

cationic particles

dialysis bag

diffusion pathway

nm pgma65phpma200 latex

situ studies

dmf gpc studies of pgma