Polymer Synthesis CHEM 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 Synthesis CHEM 421 Emulsion Polymerization External variable (surfactant concentration) used to increase BOTH molecular weight as well as rate.
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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
Polymer SynthesisCHEM 421
Variables and Other Characteristics
• Redox Initiators– Hydrogen Peroxide w/ Ferrous Ion
• Surfactant-Free Emulsion Polymerization– Initiator fragment affords amphiphilic character
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
++
+
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+
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+
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++ + + +
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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.