Transcript Polymer Synthesis CHEM 421

Heterogeneous Polymerizations
• Precipitation
• Suspension
• Dispersion
• Emulsion
Polymer Synthesis
CHEM 421
• 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
Polymer Synthesis
CHEM 421
Particle Size
(µm)
Precipitation
Solution
0.01
0.1
Emulsion
Dispersion
1
10
Suspension
100
Medium
solvency
monomer: insoluble
polymer : insoluble
soluble
insoluble
soluble
soluble
Precipitation Polymerization
M M I M
M I M M I
M I
M
M
I
Solvent M
hν
or
Δ
M
I
Polymer Synthesis
CHEM 421
M
I
M
M Solvent I
P P P PP P P P
• Solvent, monomer & initiator
• Polymer becomes insoluble in the solvent
(dependent on MW, crystallinity, rate of
polymerization
• Polymerization continues after precipitation (?)
Precipitation Polymerization
Polymer Synthesis
CHEM 421
• 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
F
F
F
F
+
F
F
F
H
F
F
ORf
H
CO2
initiator
initiator
Aqueous Emulsion
or Suspension
• Uses water
• Needs surfactants
(PFOS / PFOA / “C-8”)
• Ionic end-groups
• Multi-step clean-up
CF2 CF2
Polymer Synthesis
CHEM 421
CF2 CF
n
ORf
CF2 CH2
n
Non-aqueous Grades
• Uses CFCs & alternatives
• Surfactant free
• Stable end-groups
• Electronic grades
Polymerization of
Fluoroolefins in CO2
F
F
F
F
+
F
F
F
ORf
Typical Reaction
•
•
•
•
CO2
initiator
CF2 CF2
Polymer Synthesis
CHEM 421
CF2 CF
n
ORf
Teflon PFA™, FEP™
Tefzel™
PVDF
Nafion™
Kalrez™
Viton™
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
Polymer Synthesis
CHEM 421
75 °C, 4000 psig,  = 20 minutes
2
1.1 M
1.7M
1.9 M
2.7 M
2.9 M
dwt/d(log M)
1.5
1
0.5
0
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1.0E+07
Molecular Weight
Bimodal MWDs observed when [VF2]0
greater than about 1.9 M
Suspension Schematic
Polymer Synthesis
CHEM 421
Suspension Polymerization
Polymer Synthesis
CHEM 421
Aqueous Continuous phase
• Vertical flow pattern
• Presence of stabilizers
Addition of
monomer
dispersed phase
• Controlled agitation
• Coagulation prevented
• Particle diameter range
30mm to 2mm
Suspension
polymerization in
polymer micro-droplets
Monomer beads
Polymer beads
Method of Separation
Polymer Synthesis
CHEM 421
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
Suspension Polymerization
Polymer Synthesis
CHEM 421
• 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
Polymer Synthesis
CHEM 421
• 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, nonsolvent 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
Sample
Polymer Synthesis
CHEM 421
1 mm
Scanning electron micrographs
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
Polymer Synthesis
CHEM 421
• 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
CO2 is a Variable and
Controllable Solvent
Polymer Synthesis
CHEM 421
Pressure
• Like a gas - but high density
SCF
Liquid
• Low viscosity, high diffusivity
Pc
Solid
Gas
Tc
Temperature
Gas
Gas/Liq.
• Like a liquid - but low surface tension
SCF
• Nonflammable, environmentally friendly,
cost effective, processes at moderate P, T
Solubility in CO2
Polymer Synthesis
CHEM 421
CH3
Pressure
1- Phase
CH2
O
Ideal coils
critical point
Dilute globules
2- Phase
Concentration
C
C
n
O
CH2
C6F12
CF3
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”
1)
2)
Fluoropolymers
Siloxanes
3)
Poly(ether carbonates)…
Beckman et. al. Nature
Polymer Synthesis
CHEM 421
“CO2-phobic”
Oleophilic
Hydrophilic
PPO
PVAc
PIB
PS...
PEO
PAA
PVOH
PHEA...
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.
“Synthesis of Fluoropolymers in Supercritical Carbon Dioxide”
Polymer Synthesis
DeSimone et. al. Science 1992, 257, 945-947
CHEM 421
R
CH2
•
•
•
•
•
CO2
C
C
O
O
CH2
1,2
CF2
F
4-8
R
CH2
C
C
O
O
CH2
n
1,2
CF2
F
4-8
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
M
I
M
I
M
M
M
M
M
I
M
M
homogeneous
M
I
M
initiation
particle
nucleation
M
M
Δ
Polymer Synthesis
CHEM 421
M
M
M
I
M
M
I
M
M
M
I
M
Particle growth
monomer
initiator
stabilizer
polymer
dispersed polymer particles grow
Dispersion Polymerization
Polymer Synthesis
CHEM 421
• 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
“Dispersion Polymerizations in Supercritical Carbon Dioxide”
Polymer Synthesis
DeSimone et. al. Science 1994, 265, 356-359.
CHEM 421
Monomer
+
Surfactant + Initiator
•
•
•
•
•
•
•
•
•
CO2
heat
Polymer
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
CH 3
CH 2
Polymer Synthesis
CHEM 421
CH 3
C
C
n
O
O
CH 2CH
CH 2
CH 2
C
C
n
O
O
CH 2CH 2N=C=O
O
Poly(glycidyl methacryate)
(PGMA)
Poly(isocyanatoethyl methacrylate)
(PIEM)
• Reactive epoxy functionality
• Reactive isocyanate functionality
• Can react with amines, enzymes…
• Isocyanates react with water, alcohols…
• Can react in an epoxy resin
• 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
Polymer Synthesis
CHEM 421