CHEMCA
EXAM MASTER REVIEW SHEET
Organic Chemistry: Polymers
1. Classification by Molecular Forces
The mechanical properties of polymers depend on the strength of intermolecular forces.
Weakest intermolecular forces (van der Waals). High elasticity due to cross-links.
Example: Buna-S, Buna-N, Neoprene.
Strongest intermolecular forces (H-bonding or dipole-dipole). High tensile strength.
Example: Nylon 6,6, Terylene.
Forces intermediate between elastomers and fibres. Soften on heating, harden on cooling.
Example: Polythene, PVC, Polystyrene.
Extensively cross-linked. Undergo permanent chemical change on heating; cannot be reused.
Example: Bakelite, Melamine.
2. Important Addition Polymers
| Polymer | Monomer Unit(s) | Key Property / Use |
|---|---|---|
| LDP (Low Density) | Ethene (High pressure/Oxygen cat.) | Highly branched; Squeeze bottles. |
| HDP (High Density) | Ethene (Ziegler-Natta Catalyst) | Linear; Buckets, pipes. |
| Teflon (PTFE) | Tetrafluoroethene ($CF_2=CF_2$) | Chemically inert; Non-stick cookware. |
| PAN (Orlon) | Acrylonitrile ($CH_2=CH-CN$) | Wool substitute for blankets. |
3. Condensation Polymers
Nylon 6,6 (Polyamide)
Monomers: Adipic Acid + Hexamethylenediamine.
• High tensile strength, used in bristles for brushes.
Terylene / Dacron (Polyester)
Monomers: Ethylene glycol + Terephthalic acid.
• Crease resistant; blended with cotton (Poly-cot).
Bakelite (Phenol-Formaldehyde)
Linear intermediate is Novolac.
• Cross-linked thermosetting plastic; used in electrical switches.
Nylon 6
Monomer: Caprolactam (obtained from Cyclohexane).
• Used in tyre cords and ropes.
4. Natural & Synthetic Rubbers
Linear polymer of Isoprene (2-methyl-1,3-butadiene).
Configuration: Cis-1,4-polyisoprene.
Vulcanization:
Heating raw rubber with Sulfur ($3-5\%$) to create cross-links, improving stiffness and elasticity.
Buna-S
1,3-Butadiene + Styrene. Used in auto tyres.
Buna-N
1,3-Butadiene + Acrylonitrile. Oil resistant; used in tank linings.
5. Biodegradable Polymers
3-Hydroxybutanoic acid + 3-Hydroxypentanoic acid.
Used in specialty packaging and orthopedic devices.
Alternating polyamide of Glycine and Amino caproic acid.
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