Heterogeneous Polymerizations

1. 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

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

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

4. 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…

5. Conventional Polymerization of Fluoroolefins Aqueous Emulsionor 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

6. Polymerization of Fluoroolefins in CO2 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 Teflon PFA™, FEP™ Tefzel™ PVDF Nafion™ Kalrez™ Viton™ Romack, T. J.; DeSimone, J.M. Macromolecules1995, 28, 8429.

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

8. Suspension Schematic

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

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

11. 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

12. 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

13. 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 m 1 1 1 1 1 1 1 1 m m m m m m m m 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)

14. 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

15. 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

16. Solubility in CO2 1- Phase Pressure Ideal coils critical point Dilute globules 2- Phase Concentration • 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. Science1992, 257, 945-947 “SANS of Fluoropolymers Dissolved in Supercritical CO2”; DeSimone et. al. J. Am. Chem. Soc.1996, 118, 917.

17. Polymer Solubility in CO2 “CO2-philic” “CO2-phobic” OleophilicHydrophilic 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. Science1992, 257, 945-947 “Dispersion Polymerizations in Supercritical Carbon Dioxide” DeSimone et. al.Science1994, 265, 356-359.

18. “Synthesis of Fluoropolymers in Supercritical Carbon Dioxide” DeSimone et. al. Science1992, 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

19. Dispersion Mechanism M M Δ M M initiation M M M I I particle nucleation M I M M M Particle growth dispersed polymer particles grow M M M I I M M M M I M M M homogeneous Mmonomer Iinitiator stabilizer polymer

20. 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

21. “Dispersion Polymerizations in Supercritical Carbon Dioxide” DeSimone et. al.Science1994, 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

22. 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

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