Transcript Molecular Shape of Polymers Polymer chains are not necessarily straight! A single polymer chain Bending and coiling of polymer chains.

Molecular Shape of Polymers
Polymer chains are not necessarily straight!
A single polymer chain
Bending and coiling of polymer chains
Molecular Configurations
Isomers
mer
H H H H H H
C C C C C C
H Cl H Cl H Cl
H H H H H H H H
C C C C C C C C
H Cl Cl H H Cl Cl H
Polyvinyl chloride (PVC)
Head-to-Tail Configuration
H H H H
C C C C
H Cl H Cl
Isotactic Configuartion
Head-to-Head Configuration
H H H Cl H H H Cl
C C C C C C C C
H Cl H H H Cl H H
Syndotactic Configuration
H H H H H Cl H H
C C C C C C C C
H Cl H Cl H H H Cl
Atactic Configuration
Geometrical Isomerism
Natural rubber
H
CH3 H
H
C
C
C
C
“cis”
H
H
Polyisoprene
Gutta percha
H
CH3
C
C
H
H
C
C
H
H
“trans”
The change in the configuration cannot be achieved by
simple rotation of the double bond!
Copolymers
Copolymers: Having more than one type of “mer” unit.
Random
Block
Alternating
Graft
Properties are improved by combining different “mers”.
Polymer Crysrtallinity
crystalline
region
amorphous
region
 Usually the elastic modulus and
strength increase with increasing
the % of the crystalline regions.
 Heating (annealing) can
increase the % of the crystalline
regions.
Crystalline polyethylene
Polyethylene Crystals
Adapted from Callister, Figures 14-12 through 14-15
From dilute solution
Chain-folded structure
From melt
Spherulite Structure