Post on 17-Dec-2015
Polymer SynthesisCHEM 421
Emulsion Polymerization
• 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
Polymer SynthesisCHEM 421
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
Polymer SynthesisCHEM 421
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
Polymer SynthesisCHEM 421
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» Like acrylamide
–Oil-soluble initiator–Surfactant
Polymer SynthesisCHEM 421
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
Polymer SynthesisCHEM 421
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
Polymer SynthesisCHEM 421
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 andsurfactant
by extraction and dialysis
Polymer SynthesisCHEM 421
Designing Polymeric Nanogels
NanogelsMonomers
PEGdiacrylate n=8
2-Hydroxyethylacrylate
2-Acryloxytrimethyl-ammonium chloride
Increasing Crosslinker
Incr
easi
ng
Ch
arg
e
++
+
++
+
+
++
+
+
++
+
+
+
++
+
++
+
+
++
+
+++
++ + + +
+
++
+
++
+
++
++ +
++
OO
O
O
O
n
OHO
O
NO
O CH3 Cl -
CH3
CH3+
Polymer SynthesisCHEM 421
Dynamic Light Scattering of Microemulsions Before and After
Polymerization
Dia
me
ter
(nm
)
Crosslinker Concentration (wt %)
0
20
40
60
80
100
0 10 20 30 40 50 60
= 0% Cationic Monomer
= 12% Cationic Monomer
= 25% Cationic Monomer
Before Polymerization
After Polymerization
AfterBefore
Polymer SynthesisCHEM 421
Crosslinked Particles Adsorbed to Surface
Low Crosslinking
High Crosslinking
Polymer SynthesisCHEM 421
TEM Images of Nanogels
3% Crosslinker 12% Crosslinker 50% Crosslinker
0% C
har
ge
12%
Ch
arg
e
66K Magnification Samples Stained with 1% PTA
Polymer SynthesisCHEM 421
Release of DNA 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%
Polymer SynthesisCHEM 421
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
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
Polymer SynthesisCHEM 421
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
Polymer SynthesisCHEM 421
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
Polymer SynthesisCHEM 421
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• pH Control
– Hollow particles
Polymer SynthesisCHEM 421
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
Polymer SynthesisCHEM 421
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 particles using 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