Question
Compare the preparation, properties, and uses of nylon 6,6, PVC, Teflon, and Bakelite. What makes each polymer suitable for its specific application?
(NEET + CBSE Board — recall + application)
Solution — Step by Step
| Polymer | Monomer(s) | Polymerization | Key Property | Uses |
|---|---|---|---|---|
| Nylon 6,6 | Hexamethylene diamine + adipic acid | Condensation | High tensile strength, lustrous, elastic | Textiles, ropes, toothbrush bristles, parachutes |
| Nylon 6 | Caprolactam (ring-opening) | Addition (ring-opening) | Similar to nylon 6,6, slightly lower melting point | Tyre cords, carpets, fabrics |
| PVC | Vinyl chloride (CH₂=CHCl) | Addition | Tough, resistant to chemicals, fire-retardant | Pipes, insulation, flooring, raincoats |
| Teflon (PTFE) | Tetrafluoroethylene (CF₂=CF₂) | Addition | Extremely low friction, chemical resistance, heat stable | Non-stick cookware, gaskets, seals, surgical implants |
| Bakelite | Phenol + formaldehyde | Condensation | Thermosetting, excellent electrical insulator, heat resistant | Electrical switches, handles, radio cabinets |
| Polythene (LDPE) | Ethylene (CH₂=CH₂) | Addition (high P, trace O₂) | Flexible, transparent, branched | Carry bags, squeeze bottles, packaging |
| Polythene (HDPE) | Ethylene (CH₂=CH₂) | Addition (Ziegler-Natta catalyst) | Rigid, tough, linear | Buckets, dustbins, pipes |
- Nylon 6,6: The amide groups form strong hydrogen bonds between chains → high tensile strength and fibre-forming ability
- PVC: The C-Cl bond makes it rigid and fire-retardant (HCl released inhibits flames). Adding plasticisers makes it flexible
- Teflon: C-F bonds are among the strongest in organic chemistry. Fluorine’s small size and electronegativity create a non-reactive, non-stick surface
- Bakelite: Extensive cross-linking between phenol rings creates a 3D network that cannot be melted → permanent shape after moulding
Nylon 6,6 gets its name from the number of carbon atoms in each monomer: hexamethylene diamine has 6 carbons, adipic acid has 6 carbons. Nylon 6 has a single monomer (caprolactam) with 6 carbon atoms. This naming convention is a NEET favourite.
graph TD
A[Industrial Polymers] --> B[Fibres]
A --> C[Plastics]
A --> D[Thermosetting]
B --> B1["Nylon 6,6 — textiles"]
B --> B2["Polyester — fabrics"]
C --> C1["PVC — pipes"]
C --> C2["Polythene — bags"]
C --> C3["Teflon — non-stick"]
D --> D1["Bakelite — switches"]
D --> D2["Melamine — crockery"]
style A fill:#fbbf24,stroke:#000,stroke-width:2px
style B fill:#f9a8d4,stroke:#000
style C fill:#93c5fd,stroke:#000
style D fill:#fca5a5,stroke:#000Why This Works
The properties of a polymer are determined by: the monomer structure, the type of polymerization (addition vs condensation), the degree of branching, and the intermolecular forces. This is why polythene (simple C-H chains, weak van der Waals) is a soft plastic, while nylon (amide groups, strong H-bonds) is a tough fibre, and Bakelite (cross-linked phenol network) is a hard thermoset.
Common Mistake
Students often confuse LDPE and HDPE. LDPE is made under high pressure with peroxide initiator — it has branched chains and is soft/flexible (carry bags). HDPE is made with a Ziegler-Natta catalyst — it has linear chains, higher density, and is rigid (buckets, pipes). NEET tests the conditions and catalyst difference between these two.
Memory shortcut: Teflon = Fluorine (PTFE — polytetrafluoroethylene). The C-F bond is what makes Teflon non-stick and chemically inert. If NEET asks “which polymer is used in non-stick cookware?” — the answer is always Teflon/PTFE. Another classic: “Which polymer is an electrical insulator used in switches?” — Bakelite.