Emulsion Polymerization
Polymer Synthesis
CHEM 421
• 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 (C8 issue), etc
Variables and Other Characteristics
Polymer Synthesis
CHEM 421
• 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
Polymer Synthesis
CHEM 421
• 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
Polymer Synthesis
CHEM 421
• Standard emulsion polymerization uses
water as the continuous phase, or oil-inwater (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
» Like acrylamide
–Oil-soluble initiator
–Surfactant
Surfactants
Polymer Synthesis
CHEM 421
H2O
Oil
Surfactant Assemblies - Rich Morphologies
Water
1%
2%
1%
V
VV-
2%
3%
4% R
3%
V+L a
Multi
M
5% CTAT
cationic
surfactant
4%
5% SDBS
1%
2%
3%
4%
anionic
surfactant
V
Vesicles
R
Rod-like Micelles
M
Micelles
Multi
Multiphase Region
V+La
Vesicles and Lamellar Phase
Controlled Radical Polymerization in Microemulsion
Monomer-Swollen
Micelles
Monomer
Diffusion
M
P•
M
M
M
M
PM•
Polymer
Particle
M
M
1.0
0.6
[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
0.4
0.2
RI Response
0.8
Conversion (f)
Microemulsion
Nanoparticles
[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
0.0
0
30
60
90
120
Time (mins)
150
180
4
8
12
16
Elution Time (mins)
Liu, S. Y.; Kaler, E. W. et al. Macromolecules 2006, 39, 4345
Design of Polymeric Nanogels
for DNA Delivery
Polymer Synthesis
CHEM 421
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
Release of DNA
Diffusion Pathway
McAllister, K.; Sazani, P.; Adam, M.; Cho, M.; Rubinstein, M.; Samulski, R. J.; DeSimone*, J. M. J. Am. Chem.
Soc. 2002, 15198-15207
Microemulsion Polymerization
and Isolation of Nanogels
Addition of
Initiator to
oil phase and
free radical
polymerization
Step 1:
Form
microemulsion
Polymer Synthesis
CHEM 421
Removal of
heptane and
surfactant
by extraction
and dialysis
Step 2:
Polymerize
microemulsion
Step 3:
Extract and
purify nanogels
Designing Polymeric Nanogels
Monomers
Nanogels
O
O
O
nO
PEGdiacrylate n=8
O
O
OH
2-Hydroxyethylacrylate
Cl -
O
O
CH 3
+ N CH
3
CH 3
2-Acryloxytrimethylammonium chloride
Increasing Crosslinker
Increasing Charge
O
Polymer Synthesis
CHEM 421
+
+
+
+
+
+
+
+
+
+ ++ +
+
+
+
+
+
+
+
+
+ +
+
+
+
+
+
+
+
+
+
+
++ + +
+
+
+
+
+
+
+
+
+
+ +
Dynamic Light Scattering of
Microemulsions Before and After
Polymerization
Polymer Synthesis
CHEM 421
= 0% Cationic Monomer
100
Diameter (nm)
= 12% Cationic Monomer
= 25% Cationic Monomer
80
60
After Polymerization
40
Before Polymerization
20
0
0
10
20
30
40
50
60
Crosslinker Concentration (wt %)
Before
After
Crosslinked Particles Adsorbed to SurfacePolymer Synthesis
CHEM 421
Low Crosslinking
High Crosslinking
TEM Images of Nanogels
12% Crosslinker
50% Crosslinker
12% Charge
0% Charge
3% Crosslinker
Polymer Synthesis
CHEM 421
66K Magnification Samples Stained with 1% PTA
Release of DNA from
Non-ionic Nanogels
Polymer Synthesis
CHEM 421
Final Fluorescence
Intensity in Bag
Initial Fluorescence
Intensity in Bag
Dialysis for 24 hours
at 37°C and at 4°C
37°C = 100%
4°C = 100%
37°C = 4%
4°C = 8%
Variables and Other
Characteristics
• Lower temperatures
–Anti-freeze
• Redox initiators
–Hydrogen peroxide w/ ferrous ion
• Surfactant free
–Initiator fragment results in amphiphilic
character
• Micro-emulsions, Mini-emulsions
• Inverse emulsions
• Core-shell particles
Polymer Synthesis
CHEM 421
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
Polymer Synthesis
CHEM 421
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:
core
is determined by thermodynamic control (lowest surface free energy)
and kinetic control. The second polymer doesn’t necessarily form the
shell!
shell
Possible Morphologies
Polymer Synthesis
CHEM 421
Thermodynamically Stable Morphologies
Core-shell
Inverted core-shell
Halfmoon A
Halfmoon B
Kinetically Trapped Morphologies
Microdomains
A
B
Raspberry
1st-stage polymer
2nd-stage polymer
Sandwich
A
B
Variables and Other
Characteristics
Polymer Synthesis
CHEM 421
• Lower temperatures
– Anti-freeze
• Redox initiators
– Hydrogen peroxide w/ ferrous ion
• Surfactant free
– Initiator fragment results in amphiphilic character
•
•
•
•
Micro-emulsions, Mini-emulsions
Inverse emulsions
Core-shell particles
pH Control
– Hollow particles
Hollow Particles & Ropaque™
Polymer Synthesis
CHEM 421
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
Lower pH
Raise pH
CH3
O
O
CH3
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
Hollow Particle Micrographs
Polymer Synthesis
CHEM 421
PMMA particles via W/O/W
emulsion polymerization
Core-shell hollow particles
using methacrylic acid
J. Poly. Sci. A: Polym. Chem., 2001, 39, 1435
Colloid Polym. Sci. 1999, 277, 252.
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
Y. T. Li and S. P. Armes, Angewandte Chem., 2010, 49, 4042
X = 30
65
O
O
O
+
HO
O
X = 100
PGMA 65 – PHPMA X
HO
HO
PGMA
PGMA
65 macroCTA
65
RAFT CTA
HPMA
HPMA
X = 300
Targeting a longer core-forming block relative to the stabiliser block
should lead to progressively larger sterically-stabilised nanolatexes?
Scanning Electron Microscopy Studies
Y. T. Li and S. P. Armes, Angewandte Chem., 2010, 49, 4042
105 nm PGMA65-PHPMA300 latex
90 nm PGMA65-PHPMA200 latex
SEM images confirm spherical, near-monodisperse latexes
Transmission Electron Microscopy Studies
Y. T. Li and S. P. Armes, Angewandte Chem., 2010, 49, 4042
PGMA65-PHPMA50
PGMA65-PHPMA70
200 nm
200 nm
Dh = 29 nm
Dh = 40 nm
Negative staining using uranyl formate:
Prof. S. Sugihara and Dr. A. Blanazs
PGMA65-PHPMA100
200 nm
Dh = 58 nm
Scale bar: 100 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,
Armes,
77.5
min = 68S.
%,P.DP
131
J. Madsen, A. J. Ryan
and G. Battaglia
JACS, 2011, ASAP
More In Situ Studies: PGMA47-PHPMAx
84 mins = 75 %, DP 150
Scale bars: 200 nm
87 mins = 78 %
DP 156
75 min = 62 %, DP 123
90 mins = 82 %, DP 164
65 min = 46 %, DP 92
225 mins = 100 %
DP 200