Polymer Synthesis CHEM 421 Heterogeneous Polymerizations • Precipitatio n • 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
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Polymer Synthesis CHEM 421 Heterogeneous Polymerizations Precipitation Suspension Dispersion Emulsion Distinguished by: – –Initial state of the polymerization.
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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
Polymer SynthesisCHEM 421
Free Radical Polymerizations
Mediumsolvency
Emulsion
monomer: insolublepolymer : insoluble
Dispersion
Precipitation
solubleinsoluble
Solution
solublesoluble
0.01
0.1
1
10
100
Particle Size (µm)
Suspension
Polymer SynthesisCHEM 421
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
Polymer SynthesisCHEM 421
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
• 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
Polymer SynthesisCHEM 421
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