polymer synthesis chem 421 emulsion polymerization external variable (surfactant concentration) used...
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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
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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
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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
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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
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Polymer SynthesisCHEM 421
Surfactants
H2O
Oil
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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
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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
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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
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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
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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+
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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
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Polymer SynthesisCHEM 421
Crosslinked Particles Adsorbed to Surface
Low Crosslinking
High Crosslinking
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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
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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%
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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
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Murthy N et al. PNAS 2003;100:4995-5000
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Miniemulsion Polymerization for Dually-Triggered Degradable Nanogels
Li, Z. C, et al. et al. J. Controlled Release 2011, 152, 57
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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
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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
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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
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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
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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
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Emulsion Polymerization for Dye-Labeled Nanoparticles
Zhu, M. Q.; Li, A. D. Q. et al. J. Am. Chem. Soc. 2006, 128, 4303
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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
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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
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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
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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….
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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