polymer synthesis chem 421 heterogeneous polymerizations precipitation suspension dispersion...

Polymer SynthesisCHEM 421

Heterogeneous Polymerizations

• Precipitation

• Suspension

• Dispersion

• Emulsion

• Distinguished by:– Initial state of the polymerization

mixture

– Kinetics of polymerization

– Mechanism of particle formation

– Shape and size of the final polymer particles


Free Radical Polymerizations

Mediumsolvency

Emulsion

monomer: insolublepolymer : insoluble

Dispersion

Precipitation

solubleinsoluble

Solution

solublesoluble

0.01

0.1

1

10

100

Particle Size (µm)

Suspension


Precipitation Polymerization

• Solvent, monomer & initiator

• Polymer becomes insoluble in the solvent (dependent on MW, crystallinity, rate of polymerization

• Polymerization continues after precipitation (?)

SolventSolvent

M

M M

MM

MM

MM

M

I

I

II

I

hνorΔ

M M

M

MI

I

I

P P PP PPP P


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 Emulsionor Suspension Non-aqueous Grades

• Uses water• Needs surfactants (PFOS / PFOA / “C-8”)• Ionic end-groups• Multi-step clean-up

F

F

F

F

F

F

ORf

FCF2 CF2 CF2 CF

ORfninitiator

CO2+

F

F

H

HCF2 CH2

ninitiator

• Uses CFCs & alternatives• Surfactant free• Stable end-groups• Electronic grades


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

Romack, T. J.; DeSimone, J.M. Macromolecules 1995, 28, 8429.

F

F

F

F

F

F

ORf

FCF2 CF2 CF2 CF

ORfninitiator

CO2+

Teflon PFA™, FEP™Tefzel™ PVDFNafion™Kalrez™Viton™


GPC Traces - Effect of [VF2] on MWD

0

0.5

1

1.5

2

1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07Molecular Weight

dw

t/d

(lo

g M

)

1.1 M

1.7M

1.9 M

2.7 M

2.9 M

Bimodal MWDs observed when [VF2]0

greater than about 1.9 M

75 °C, 4000 psig, = 20 minutes


Suspension Schematic

Polymer SynthesisCHEM 421Suspension Polymerization

Aqueous Continuous phase

• Vertical flow pattern • Presence of stabilizers

Addition ofmonomerdispersed phase

Monomer beadsPolymer beads

Suspension polymerization in

polymer micro-droplets• • Controlled agitationControlled agitation• • Coagulation preventedCoagulation prevented• • Particle diameter rangeParticle diameter range 3030m to 2mmm to 2mm


Method of Separation

100m

100m

Broad size distribution

* All pictures are optical micrographs

250m sieve

Copolymer particles separated into fractionswith US standard sieves using a sieve shaker

Particles after sieving

125m sieve

75m sieve

45m sieve


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 potential by incorporating various porogens (solvent, non-solvent or linear polymer)

Toluene has been successfully investigated

• Porosity evaluation by performing SEM and N2-BET

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

• Application to transition-metal catalysis and enzymatic catalysis

Porosity Investigations


Porosity Investigations

1 m1 m

1 mm 1 mm

1 m1 m

1 mm 1 mm

1 m1 m

1 mm 1 mm

1 m1 m

1 mm 1 mm

Scanning electron micrographs1 m1 m

1 mm 1 mm

1 mm

1 mm 1 mm

1 mm

1 mm 1 mm

1 m1 m

1 mm 1 mm

Scanning electron micrographs

Visual Appearance of Cross-linked fluoropolymer beads

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)


• 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

Potential Utility of CO2


Gas Gas/Liq. SCF

• 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

CO2 is a Variable and Controllable Solvent

Pre

ssu

re

Tc

Temperature

Pc

LiquidSCF

Gas

Solid

Polymer SynthesisCHEM 421Solubility in CO2

2- Phase

1- Phase

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

CH2 C

CO

O

CH2

C6F12

CF3

CH3

n

“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”

1) Fluoropolymers2) Siloxanes

3) Poly(ether carbonates)… Beckman et. al. Nature

Oleophilic Hydrophilic

PPO PEOPVAc PAAPIB PVOHPS... PHEA...

f(MW, morphology, topology, composition, T, P)

“Dispersion Polymerizations in Supercritical Carbon Dioxide” DeSimone et. al. Science 1994, 265, 356-359.




CH2 C

R

C O

O CH2 CF2 F

CH2 C

R

C O

O CH2 CF2 F1,2 4-81,2 4-8

CO2

n

• 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

MM

MII

I

M

MM

MMM

M

homogeneous

initiation

particlenucleation

Δ

M monomer I initiator

stabilizerpolymer

Particle growth

dispersed polymer particles grow

M

M

M

M

M

MM

IM

M

M

M

I

I


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 + InitiatorCO2

heatPolymer

• 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

“Dispersion Polymerizations in Supercritical Carbon Dioxide” DeSimone et. al. Science 1994, 265, 356-359.


Structured Particles Containing a Reactive Functional Polymer

CH2 C

CH3

Cn

O

O

CH2CH CH2

O

Poly(glycidyl methacryate)(PGMA)

Poly(isocyanatoethyl methacrylate)(PIEM)

CH2 C

CH3

Cn

O

O

CH2CH2N=C=O

• 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


Composition: 14 mol% PIEM

86 mol% PS

CH2 C

CH3

Cn

O

O

CH2CH2N=C=O

CH2 CHn

100 nm

TEM Images of PIEM/PS

polymer synthesis chem 421 heterogeneous polymerizations precipitation suspension dispersion...

Documents

polymer synthesis chem

insoluble polymer

suspension slide

monomer slide

sieve slide

monomer initiator polymer

final polymer particles

polymer microdroplets