Transcript General Approaches to Polymer Synthesis

General Approaches to Polymer Synthesis
• 1. Addition
Chain Growth
Polymerization of Vinyl Monomers
Ring Opening Polymerization
Heterocylics
Metathesis of Cyclic Olefins
2.
3.
Condensation
Step Growth
Polymerization of A-B or AA/BB Monomers
Modification of Preformed Polymers
Polysaccharides
Peptides and Proteins
Synthetic Precursors
Current Strategies in Polymer Synthesis
• Objectives: Precise Macromolecular Design
• 1
–
–
–
–
. Control of: Molecular Weight
Molecular Weight Distribution
Composition
Sequence of repeat units
Stereochemistry
• 2. Versatility
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Free Radical Initiated Polymerization
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Classical Free Radical Process
Applied to wide range of monomers
Broad scope of experimental conditions
Molecular weight can be controlled
Mw/Mn > 1.5  2.0 
Statistical compositions and sequences
Little stereochemical control
Anatomy of Addition Polymerizations
• Initiation
– Generation of active initiator
– Reaction with monomer to form growing chains
• Propagation
– Chain extension by incremental monomer addition
• Termination
– Conversion of active growing chains to inert polymer
• Chain Transfer
– Transfer of active growing site by terminating one
chain and reinitiating a new chain.
Polymerizability of Vinyl Monomers
Active Centers must be stable enough to persist
though multiple monomer additions
X
X
anionic
X
cationic
radical
• Typical vinyl monomers
CN
O
CH3
O
R
O
O
OEt
Polymerizability of Vinyl Monomers
Monomers
Ethylene
Radical Cationic
Anionic Complex
Metal
+
+
+
-
+
-
+/+
1,2-Dialkyl
olefins
-
+
-
+
1,3-Dienes
+
+
+
+
+
+
+
+
Propylene
1,1-Dialkyl
olefins
Styrenes
Polymerizability of Vinyl Monomers
Monomers
VCl
Radical Cationic
Anionic Complex
Metal
+/+
-
+
+
+
-
Acrylonitriles
/ Acrylamides
+
-
+
-
Vinyl ethers
+
+
+/-
+/-
+/-
Vinyl esters
Acylates/
methacrylates
Substituted
Styrenes
Types of Vinyl Polymerization
Method
Advantages
Disadvantages
Bulk (Neat)
Simple equipment
Rapid reaction
Pure polymer isolated
Heat buildup
Gel effect
Branched or crosslinked product
Solution
Good mixing
Ready for application
Lower mol. Wt.
Low Rpoly
Solvent Recovery
Suspension
(Pearl)
Low viscosity
Direct bead formation
Removal of additives
Emulsion
High Rpoly
Low Temperatures
High Mol. Wt.
High surface area latex
Removal of additives
Coagulation needed
Latex stability
Inverse Emulsion Water in oil latex
formed
Inversion promotes
dissolution in water
Thermodynamics of Polymerization
X
X
X
X
Gp = Hp-TSp
Hp < 0
-bond  -bond
Sp < 0
Loss of translational entropy
Polymerization favored below a ceiling temperature, Tc
Tc =

S
Thermodynamics of Polymerization
Monomer
-Hp,
kJ/mole
-Sp,
J/K-mole
Tc, K (C)
Observed
Ethylene
93
155
600 (327)
400
MMA
56
104
478(205)
220
a-Methyl
styrene
35
110
318 (45)
61
Isobutylene
48
121
326 ( 123)
50
Suspension Polymerization
Equivalent to a "mini-bulk" polymerization
Advantages
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Aqueous (hydrocarbon) media provides good heat transfer
Good particle size control through agitation and dispersion agents
Control of porosity with proper additives and process conditions
Product easy to recover and transfer
Disadvantages
• Suspending Agents contaminate product
• Removal of residual monomer necessary
Suspension (Pearl) Polymerization
Process Type
Aqueous Phase
Monomers Used
Product
BEAD
Polymer Soluble in
Monomer
 1% Sol. Polymer
Suspending Agents
Cu++ Inhibitors
Styrene
Methyl Methacrylate
Vinyl Acetate
Clear Beads
POWDER
Polmer Insoluble in
Monomer
Suspending Agents
Electrolytes
Vinyl Chloride
Acrylonitrile
Fluoroethylene
Opaque Beads or
Powders
INVERSE
Hydrocarbon Media
Monomer
Initiator
Acrylamide
Acrylic Acids
Beads

Emulsions
Suspension Polymerization of Styrene
Temp
Monomer Phase
16.6 Kg. Styrene
(0.5 kg Methacrylic Acid)
0.012 kg AIBN
0.006 kg Benzoyl Peroxide
0.015 kg tert-Butyl Perbenzoate
Aqueous Phase:
16.6 Kg of H2O
0.24 kg Ca3PO4
0.14 kg Na+ Naphthalene sulfonate
0.077 kg. 15% Sodium Polyacrylate
Polymerization Time. Hours
EMULSION POLYMERIZATION
• Advantages:
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High rate of polymerization
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High molecular weights
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Few side reactions
High Conversion achieved
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Efficient heat transfer
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Low viscosity medium Polymer never in solution
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Low tendancy to agglomerate
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Emulsified polymer may be stabilized and used directly
Disadvantages:
Polymer surface contaminated by surface active agents
Coagulation introduces salts;Poor electrical properties
Components of Emulsion Polymerization
M onom er
P o ly m e r
M onom er
D ro p le t
5 0 0 -2 0 0 0 A
M o n o m e r M ic e lle 2 0 -3 0 A
R.
Water soluble initiator
M o n o m e r D ro p le t
1 0 ,0 0 0 A (1  )
POLYMERS PRODUCED USING
EMULSION PROCESSES
Polymer
Applications
Styrene-Butadiene Rubber
(SBR)
Tires, Belting, Flooring,
Molded goods, Shoe soles, Electrical
insulation
Butadiene-Acrylonitrile (nitrile
Fuel tanks, Gasoline hoses, Adhesives,
Impregnated paper, leather and textiles
rubber)
Acrylonitrile-Butadiene-Styrene Engineering plastics, household appliances,
(ABS)
Automobile parts, Luggage
Polyacrylates
Water based latex paints
Major Developments in the 1950-60's
Living Polymerization (Anionic)
• Mw/Mn  1
• Blocks, telechelics and stars available
(Controlled molecular architecture)
• Statistical Stereochemical Control
• Statistical Compositions and Sequences
• Severe functional group restrictions
Ziegler-Natta (Metal-Coordinated)
Polymerization
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Stereochemical Control
Polydisperse products
Statistical Compositions and Sequences
Limited set of useful monomers, i.e. olefins
• SINGLE SITE CATALYSTS
Polyolefins
• Polypropylene (1954)
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PP
dishwasher safe plastic ware, carpet
yarn, fibers and ropes, webbing, auto parts
H
IsotacticH
X
Tacticity
H
X
X
X
X
X
All asymmetric carbons have same configuration
• Methylene hydrogens are meso
• Polymer forms helix to minimize substituent interaction
Syndiotactic
H
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X X
X X
X X
Asymmetric carbons have alternate configuration
Methylene hydrogens are racemic
Polymer stays in planar zig-zag conformation
Heterotactic (Atactic)
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Asymmetric carbons have statistical variation of configuration
Additional Developments in the 1980's
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"Immortal" Polymerization (Cationic)
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–
–
–
–
Mw/Mn  1.05
Blocks, telechelics, stars
(Controlled molecular architecture)
Statistical Compositions and Sequences
Severe functional group restrictions
Free Radical Initiated Polymerization
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Controlled Free Radical Polymerization
Broad range of monomers available
Accurate control of molecular weight
Mw/Mn  1.05 --Almost monodisperse
Blocks, telechelics, stars
(Controlled molecular architecture)
Statistical Compositions and Sequences
Genetic Approaches via Modified
Microorganisms
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Monodisperse in MW
Monodisperse in Composition
Sequentially Uniform
Stereochemically Pure
Diverse set of functional groups possible
through synthesis of novel amino acids
Commodity Polyolefins
Polyethylene
High Density (1954)
HDPE
Bottles, drums, pipe, conduit, sheet, film
Low Density (1939-1945)
LDPE
Packaging Film, wire and cable coating, toys, flexible
bottles, house wares, coatings
Linear Low Density (1975)
Shirt bags, high strength films
LLDE
Commodity Polyolefins
Polypropylene (1954)
PP
dishwasher safe plastic ware, carpet yarn, fibers and ropes,
webbing, auto parts
Polyisobutylene (1940)
PIB
inner tubes, flexible adhesives, raincoats
Commodity Vinyl Polymers
Polystyrene (1920)
PS
Styrofoam, clear plastic cups
envelop windows, toys
Cl
Poly(vinyl chloride) (1927)
Cl
Cl
Cl
PVC
garden hose, pipe, car trim, seat covers, records,
floor tiles
Semi-Commodity Polymers
CO CH
Poly(methyl methacrylate) (1931)
CO CH CO CH
CO CH
CO CH
PMMA
plexiglas, embedding resin, resist for X-ray applications
F
Polytetrafluoroethylene. (1943)
teflon, non stick cookware, no grease bearings,
pipe-seal tape
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
Commodity Condensation Polymers
O
N
H
C
H
Nylon 6 /
bearings, molded parts
carpet yarn
marine rope
cooking/boiling bags
N
H
N
O
C
C
O
Nylon 66 (1939)
Fibers, tire cord, fishing line
Commodity Condensation Polymers
O
O
C
C
O
O
Polyester (1941)
PET, dacron, mylar, kodel
fibers, film-backing, magnetic tapes, soft drink bottles, tire
cord, moldings
O
Polycarbonate (1957)
PC, Lexan
shatter proof glass, cd-disks, car doors and roofs,
appliance housings
O
O