1. CHAPTER 14
Polymer Structures

2. INTRODUCTION
Natural Polymers  Leather, wood, rubber, cellulose, cotton, wool.
Synthetic polymers Synthesized from small organic molecules.
CHEMISTRY OF POLYMER MOLECULES
Hydrocarbons (many organic materials)= composed of hydrogen and carbon
Covalent Bonding
H-C-H H
Methane
Ethylene
Similarly

3. POLYMERISATION
Mers = small structural entities making up the ‘poly’mer.
Ethylene(C2H4) gas
CAN BE CONVERTED TO POLYETHYLENE(PE) Solid
Catalyst
bonding unsatisfied for this C atom
bonding satisfied for C atom

4. RESULT
Angle =109o

5. Similarly
Unpaired electron
Methyl group

7. MOLECULAR WEIGHT Number average Weight-average
Not all chains same length
Weight-average

8. For copolymers
Degree of polymerization
Molecular weight of mer j

9. Branched Linear Crosslinked Network e.g. Polyethylene, Nylon
Lower density
Crosslinked
Network
e.g. Rubber
e.g. Epoxy

10. HOMOPOLYMERS COPOLYMERS Polymers composed of two
or more different ‘mer’ units
Bifunctional, trifunctional mers

11. Styrene-butadiene rubber (SBR) random copolymer
Used in automobile tires.

12. POLYMER CRYSTALLINITY
= Packing of molecular chains so as to produce an ordered atomic array.
Small molecules (Methane, H2O)  either either totally crystalline (as solids)
or amorphous (as liquids)
However POLYMERS  only partially crystalline (semi-crystalline)
Max. crystallinity  ~ 95%.

13. Properties greatly affected by degree of crystallinity
(crystalline = stronger and more resistant to
softening by heat.
 important to quantify degree crystallinity
Crystalline polymer = higher density

14. Slower cooling rates from the melt favor higher crytallinity
(giving time for ordered configurations)
Linear Polymers Crystallization easily accomplished, since no restriction to
chain alignment
Branched polymers NEVER highly crystalline
Side branches interfere with crystallization
Network Polymers  AMORPHOUS
COPOLYMERS
More Irregular and random mer  less crystallinity
Alternating and block copolymers  likelihood of crystallization.
Random and Graft copolymers Normally Amorphous