Molecular Shape of Polymers Polymer chains are not

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Molecular Shape of Polymers Polymer chains are not necessarily straight! A single polymer chain

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 C C C H Cl H H

Molecular Configurations Isomers mer H H H C C C H Cl H H H H C C C C H Cl Cl H Polyvinyl chloride (PVC) Head-to-Tail Configuration H H C C H Cl Isotactic Configuartion Head-to-Head Configuration H H H Cl C C C C H Cl H H Syndotactic Configuration H H H Cl H H C C C C H Cl H H H Cl Atactic Configuration

Geometrical Isomerism Natural rubber H CH 3 H H C C “cis” H H

Geometrical Isomerism Natural rubber H CH 3 H H C C “cis” H H Polyisoprene Gutta percha H CH 3 C C H H “trans” The change in the configuration cannot be achieved by simple rotation of the double bond!

Copolymers: Having more than one type of “mer” unit. Random Block Alternating Graft Properties

Copolymers: Having more than one type of “mer” unit. Random Block Alternating Graft Properties are improved by combining different “mers”.

Polymer Crysrtallinity Ø Usually the elastic modulus and strength increase with increasing the %

Polymer Crysrtallinity Ø Usually the elastic modulus and strength increase with increasing the % of the crystalline regions. Ø 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

Polyethylene Crystals Adapted from Callister, Figures 14 -12 through 14 -15 From dilute solution Chain-folded structure From melt Spherulite Structure