Heterogeneous Polymerizations

1
Heterogeneous Polymerizations

• Precipitation
• Suspension
• Dispersion
• Emulsion

2
Free Radical Polymerizations
Solution
Precipitation
Emulsion
Dispersion
Suspension
Medium solvency
monomer insoluble polymer insoluble
soluble insoluble
soluble soluble
3
Precipitation Polymerization

• 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
Teflon PFA, FEP Tefzel PVDF Nafion Kalrez Vi
ton

• Typical Reaction
• 10-50 solids
• 3-5 hours _at_ 35 C (batch)
• Pressures 70-140 bar at 35 C
• End group analysis (FTIR) shows 3 COOH, COF end
  groups per 106 carbons
• ltMngt 106 g/mol without chain transfer agent

Romack, T. J. DeSimone, J.M. Macromolecules
1995, 28, 8429.
7
GPC Traces - Effect of VF2 on MWD
75 C, 4000 psig, ? 20
minutes
Bimodal MWDs observed when VF20 greater than
about 1.9 M
8
Suspension Schematic
9
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
125mm sieve
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, cant 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
1
m
m
1
m
1
m
1
m
1
m
1
m
1
m
1
m
1
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m
1
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1
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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

• Scattering Studies
• Determined key molecular parameters (ltMwgt,
  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.
17
Polymer Solubility in CO2
CO2-philic
CO2-phobic
Oleophilic Hydrophilic PPO PEO PVAc PAA PIB PV
OH 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.
18
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

19
Dispersion Mechanism
M
M
M
I
I
M
M
M
M
I
M
M
M
homogeneous
M monomer I initiator 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. 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

22
Structured Particles Containing a Reactive
Functional Polymer
Poly(glycidyl methacryate) (PGMA)
Poly(isocyanatoethyl methacrylate) (PIEM)

• 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

• Reactive epoxy functionality
• Can react with amines, enzymes
• Can react in an epoxy resin

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