Heterogeneous Polymerizations Distinguished by: Initial state of the polymerization mixture Kinetics of polymerization Mechanism of particle formation Shape and size of the final polymer particles Precipitation Suspension Dispersion Emulsion

Free Radical Polymerizations 0.01 0.1 1 10 100 Particle Size (µm) Precipitation Solution Emulsion Dispersion Suspension Medium solvency monomer: insoluble polymer : insoluble soluble insoluble soluble

Precipitation Polymerization Solvent M I hν or Δ P Solvent, monomer & initiator Polymer becomes insoluble in the solvent (dependent on MW, crystallinity, rate of polymerization Polymerization continues after precipitation (?)

Precipitation Polymerization Considerations: Ease of separation Used for: Vinyl chloride (solvent free) Poly(acrylonitrile) in water Fluoroolefins in CO2 Poly(acrylic acid) in benzene Poly(acrylic acid) in CO2 Traditionally, not too applicable… Rule of thumb, polymer must be insoluble in its own monomer…

Conventional Polymerization of Fluoroolefins Aqueous Emulsion or Suspension Non-aqueous Grades Uses water Needs surfactants (PFOS / PFOA / “C-8”) Ionic end-groups Multi-step clean-up Uses CFCs & alternatives Surfactant free Stable end-groups Electronic grades

Polymerization of Fluoroolefins in CO2 Teflon PFA™, FEP™ Tefzel™ PVDF Nafion™ Kalrez™ Viton™ Typical Reaction 10-50% solids 3-5 hours @ 35 °C (batch) Pressures 70-140 bar at 35 °C End group analysis (FTIR) shows 3 COOH, COF end groups per 106 carbons <Mn> ~ 106 g/mol without chain transfer agent Romack, T. J.; DeSimone, J.M. Macromolecules 1995, 28, 8429.

GPC Traces - Effect of [VF2] on MWD 75 °C, 4000 psig,  = 20 minutes Bimodal MWDs observed when [VF2]0 greater than about 1.9 M

Suspension Schematic

polymer micro-droplets Suspension Polymerization Aqueous Continuous phase • Vertical flow pattern • Presence of stabilizers Addition of monomer dispersed phase Monomer beads Polymer beads Suspension polymerization in polymer micro-droplets • Controlled agitation • Coagulation prevented • Particle diameter range 30mm to 2mm

Method of Separation Particles after sieving Broad size distribution Copolymer particles separated into fractions with US standard sieves using a sieve shaker Broad size distribution 250mm sieve 125mm sieve 75mm sieve 100mm 45mm sieve 100mm * All pictures are optical micrographs

Suspension Polymerization Considerations: Stabilizers used: water-soluble polymers: i.e. poly(vinyl alcohol) Hard to control particle size – separate with sieves Two phase system only with shear, can’t recover colloidal system Used for: styrene, (meth)acrylic esters, vinyl chloride, vinyl acetate Chromatographic separation media, affinity columns, etc

Porosity Investigations Application to transition-metal catalysis and enzymatic catalysis Highly porous particles (high specific surface area) will permit an improved activity of the system by increasing the density of actives sites per unit of volume Porosity potential by incorporating various porogens (solvent, non-solvent or linear polymer) Toluene has been successfully investigated Porosity evaluation by performing SEM and N2-BET

Porosity Investigations Visual Appearance of Cross-linked fluoropolymer beads 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 mm 1 1 1 1 1 1 m m m m m m m m m 1 1 1 1 1 1 1 1 m m m m m m m m m S S c c a a n n n n i i n n g g e e l l e e c c t t r r o o n n m m i i c c r r o o g g r r a a p p h h s s Sample Styrene (wt%) EGDMA (wt%) FOMA (wt%) Surface Area* (m2/g) Non-porous 34 6 60 0.25 Porous 10 80 10 420** * Surface area measured by N2-BET, error 1%, ** Toluene used as porogen (100% v/v monomer)

Potential Utility of CO2 CO2 is non-toxic, cheap and readily available CO2 is a by-product from production of ammonia, ethanol, hydrogen CO2 is found in natural reservoirs and used in EOR Easily of separated and recycled CO2 has a low surface tension, low viscosity Liquid and supercritical states “convenient” Inert for many chemistries 7

CO2 is a Variable and Controllable Solvent Like a gas - but high density Like a liquid - but low surface tension Low viscosity, high diffusivity Nonflammable, environmentally friendly, cost effective, processes at moderate P, T SCF Liquid Pc Pressure Solid Gas Tc Temperature Gas Gas/Liq. SCF

Solubility in CO2 1- Phase 2- Phase Scattering Studies critical point Dilute globules Ideal coils Concentration Pressure Scattering Studies Determined key molecular parameters (<Mw>, Rg, A2) CO2 found to be a “good” solvent for fluoropolymers “Synthesis of Fluoropolymers in Supercritical Carbon Dioxide” DeSimone et. al. Science 1992, 257, 945-947 “SANS of Fluoropolymers Dissolved in Supercritical CO2”; DeSimone et. al. J. Am. Chem. Soc. 1996, 118, 917.

Polymer Solubility in CO2 “CO2-philic” “CO2-phobic” Oleophilic Hydrophilic PPO PEO PVAc PAA PIB PVOH PS... PHEA... 1) Fluoropolymers Siloxanes Poly(ether carbonates)… Beckman et. al. Nature f(MW, morphology, topology, composition, T, P) “Synthesis of Fluoropolymers in Supercritical Carbon Dioxide” DeSimone et. al. Science 1992, 257, 945-947 “Dispersion Polymerizations in Supercritical Carbon Dioxide” DeSimone et. al. Science 1994, 265, 356-359.

Homogeneous solution polymerizations (up to 65% solids) “Synthesis of Fluoropolymers in Supercritical Carbon Dioxide” DeSimone et. al. Science 1992, 257, 945-947 Homogeneous solution polymerizations (up to 65% solids) High molecular weights (ca. 106 g/mol) Supercritical or liquid CO2 Low viscosities Wide range of copolymers - solubility function of fluorocarbon content

Dispersion Mechanism Δ M monomer initiation particle nucleation homogeneous Particle growth dispersed polymer particles grow M monomer I initiator stabilizer polymer

Dispersion Polymerization Considerations: Relatively large particle size (0.5-5 μm); Typically narrow Particle Size Distribution Resulting polymer in colloid (application dependent) Not common, most examples synthesized from organic solvents, not water Major application: xerography, ink jets

Monomer + Surfactant + Initiator Polymer heat “Dispersion Polymerizations in Supercritical Carbon Dioxide” DeSimone et. al. Science 1994, 265, 356-359. CO2 Monomer + Surfactant + Initiator Polymer heat High conversion High molecular weights Stable latexes Dry powders Narrow particle size distributions Spherical particle morphology Different polymerization kinetics Composite latex particles possible Allows for new coating opportunities

Structured Particles Containing a Reactive Functional Polymer Poly(glycidyl methacryate) (PGMA) Poly(isocyanatoethyl methacrylate) (PIEM) Reactive epoxy functionality Can react with amines, enzymes… Can react in an epoxy resin Reactive isocyanate functionality Isocyanates react with water, alcohols… Difficult to synthesize in a aqueous emulsion or dispersion Can form crosslinking polyurethane linkages with an alcohol-containing polymer

TEM Images of PIEM/PS 100 nm Composition: 14 mol% PIEM 86 mol% PS