General Approaches to Polymer Synthesis

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General Approaches to Polymer Synthesis

• 1. Addition Chain Growth
• Polymerization of Vinyl Monomers

Ring Opening Polymerization Heterocylics
Metathesis of Cyclic Olefins
2. Condensation Step Growth   Polymerization of
A-B or AA/BB Monomers
3. Modification of Preformed Polymers Polysaccha
rides Peptides and Proteins   Synthetic
Precursors
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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

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Ziegler-Natta (Metal-Coordinated) Polymerization

• Stereochemical Control
• Polydisperse products
• Statistical Compositions and Sequences
• Limited set of useful monomers, i.e. olefins
• SINGLE SITE CATALYSTS

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Additional Developments in the 1980's

• "Immortal" Polymerization (Cationic)
• Mw/Mn ? 1.05
• Blocks, telechelics, stars
• (Controlled molecular architecture)
• Statistical Compositions and Sequences
• Severe functional group restrictions

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Free Radical Initiated Polymerization

• 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

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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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Genetic Approaches via Modified Microorganisms

• Monodisperse in MW
• Monodisperse in Composition
• Sequentially Uniform
• Stereochemically Pure
• Diverse set of functional groups possible through
  synthesis of novel amino acids

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Step-Growth or Condensation Polymerizations
Molecular Weight predicted by Carothers
Equation A-A B-B -A-B-x x C A-A
B-B No of functional groups remaining at
anytime N
Extent of reaction p No - N p _____
or N No (1 - p) No
Degree of Polymerization, D.P. No / N 1 / (1
- p)
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Problems in Achieving High D. P.
1. Non-equivalence of functional groups
a. Monomer impurities 1. Inert impurities
(adjust stoichiometry) 2. Monofunctional units
terminate chain
b. Loss of end groups by degradation
c. Loss of end groups by side reactions with
media
d. Physical losses
e. Non-equivalent reactivity
f. Cyclization
. Unfavorable Equilibrium Constant
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Impact of percent reaction, p, on DP
Degree of Polymerization, D.P. No / N 1 / (1
- p)
Assuming perfect stoichiometry
DPmax (1 r) / (1 - r) where r molar ratio of
reactants
if p DP
0.5 2
0.7 3.3
0.9 10
0.95 20
0.99 100
0.999 1000
if r Diacid / diol 0.99, then DPmax 199
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Cyclization
1. Thermodynamic stability
Rings of 3,4,8 lt 11 lt 7, 12 ltlt 5 ltlt 6
2. Kinetic Control
Propagation more rapid than cyclization Reduce
probability of collision for rings 12
Non-reversible propagation process
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Equilibrium in Polyesterification
Reaction in closed system
p fraction esterified
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Equilibrium in Polyesterification
Effect of Keq on extent of reaction and DP
Keq p Xn
0.01 0.1 1.11
1 0.5 2
16 0.8 5
81 0.9 10
361 0.95 20
9800 0.99 100
39,600 0.995 200
transesterification
esterification
amide formation
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Driving reaction to completion in open, driven
system
Keq DP H2O
1 2 2.5
20 0.0132
50 0.00204
100 0.000505
200 0.000126
16 5 4.0
20 0.211
50 0.0327
100 0.0081
200 0.00201
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Types of Condensation Reactions
1. Polyesters
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Preparation of Aromatic Polyesters
Stoichiometry and DP controlled by extent of
glycol removed.
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Types of Condensation Reactions
2. Polyamides
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Polyamides via Condensation -- Nylon 66
mp. 265C, Tg 50C, MW 12-15,000 Unoriented
elongation 780
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Types of Condensation Polymers
Polyesters
Polyanhydrides
Polyacetals
Polycarbonates
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Lexan Polycarbonate
Interfacial Process
Tm 270C, Tg 145-150C 10-40 Crystalline,
Brittle Temp. - 10C
Ester Interchange
No Solvent, Pure Polymer with MW gt 30,000 Formed
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Types of Condensation Polymers
polyurethanes
polyphenylene oxide
polyarylenes
polyarylene ether sulfones
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Low Temperature Condensation Polymerization

• Interfacial or Solution in Polar Aprotic Solvents

Parameter Low Temp High Temp
Intermediates
Purity Stoichiometry Heat Stability Structure Cost Moderate Not Essential Not Essential Highly Reactive High High Essential Essential Thermally stable Moderate
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Interfacial or Solution Polymerization in Polar
Aprotic Solvents (Cont)
Conditions Low Temp High Temp
Time Temperature Pressure Yield By-products Solvents Minutes to hours 0 150 ?C Atmospheric Low to moderate Salts Required Hours to days gt250 ?C High to vacuum Quantitative Volatiles None
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Applications of Low Temperature Condensations

• Prep. of Infusible Thermally Stable Polymers
• Prep. of Thermally Unstable Polymers

Prep. of Polymers Containing Functional Groups
with Differing Reactivity
Formation of Block or Ordered Polymers (No
equilibration of polymer in melt allowed)
Direct Production of Polymer Solutions for
Coatings, Spinning into Fibers, Solvent Blending
to form Composites
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Types of Condensation Polymers
polyamides
polyimides
polybenzthiazoles
polybenzoxazoles
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Aromatic Polyamides Aramids
M-isomers favor formation of soluble polymers
Unique solvent combination
Can be Dry Spun to Fiber As Spun Elongation,
23-34, Tenacity, 4.6-5.3 g/Denier
70 Strength Retained in Ionizing Radiation
M.p. gt 350 ?C
Nomex
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Polyimides for Electronic Applications
Fabricate in soluble form
Post treat to final form
Kevlar
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POLYETHERSULFONES
Bis-nucleophile
Polymerize by SnAr2
Monofunctional terminator to stabilize polymer
Use Temperature -100? to 175?C Stable in air
to 500?C, Self Extinguishing
Molecular Weight 65,000 - 250,000 Amorphous
Material, Tg ? 200?C, Films pressed at 280?C
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Polyphenylene Oxide (PPO)
Oxidative Coupling Process
Mn 30,000 to 120,000 Amorphous , Tg ? 210?C
Crystalline, Tm ? 270?C Brittle point ?
-170?C Thermally Stable to ? 370?C
Noryl is a blend with polystyrene
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Noryl is Unique Blend

• Single Phase, Tg dependent upon composition
• Maximum tensile strength at 80 wt PPO
• Other properties volume fraction weighted
  average
• Blend compatible with rubber modified polystyrene
  (high impact resistance)
• Applications of Noryl Engineering Thermoplastics
• Useful properties
• High impact resistance
• Flame retardant
• High chemical stability
• Low moisture absorbance (0.070
• Use in appliance housings
• Automobile dashboards
• Radomes, fuse boxes, wiring splice devises