Important industrial polymers — nylon, PVC, teflon, bakelite properties and uses

Question

Compare nylon-6,6, PVC, teflon, and bakelite in terms of their monomers, type of polymerisation, key properties, and industrial uses. Why is teflon chemically inert while PVC is not?

Polymer Property Comparison

flowchart TD
    A["Industrial Polymers"] --> B["Addition Polymers"]
    A --> C["Condensation Polymers"]
    B --> D["PVC — vinyl chloride"]
    B --> E["Teflon — tetrafluoroethylene"]
    B --> F["Polythene — ethylene"]
    C --> G["Nylon-6,6 — hexamethylenediamine + adipic acid"]
    C --> H["Bakelite — phenol + formaldehyde"]
    D --> I["Thermoplastic"]
    E --> J["Thermoplastic"]
    G --> K["Thermoplastic (fibre)"]
    H --> L["Thermosetting"]

Solution — Step by Step

Monomers: Hexamethylenediamine ( $\text{H}_2\text{N}$ - $(\text{CH}_2)_6$ - $\text{NH}_2$ ) and adipic acid ( $\text{HOOC}$ - $(\text{CH}_2)_4$ - $\text{COOH}$ )

Polymerisation: Condensation (step-growth). An amide bond ( $-\text{CO-NH}-$ ) forms between the amine and carboxyl groups, releasing water.

Properties: High tensile strength, elastic, lustrous, resistant to abrasion. The “6,6” refers to 6 carbon atoms in each monomer.

Uses: Textiles, ropes, carpets, tyre cords, toothbrush bristles, gears, and bearings.

Monomer: Vinyl chloride ( $\text{CH}_2\text{=CHCl}$ )

Polymerisation: Addition (chain-growth). The double bond opens and monomers chain together.

Properties: Rigid and hard in pure form, but becomes flexible when plasticisers (like phthalates) are added. Resistant to chemicals, weathering, and fire (self-extinguishing due to Cl content).

Uses: Pipes, cable insulation, flooring, window frames, blood bags, raincoats.

Monomer: Tetrafluoroethylene ( $\text{CF}_2\text{=CF}_2$ )

Polymerisation: Addition (chain-growth, free radical mechanism).

Properties: Extremely chemically inert — resists almost all acids, bases, and solvents. Very low coefficient of friction (non-stick). Withstands temperatures up to 260 degrees C.

Why is teflon so inert? The C-F bond is one of the strongest single bonds in organic chemistry (bond energy ~485 kJ/mol). The fluorine atoms form a dense shield around the carbon backbone, making it almost impossible for any reagent to attack. Compare this with PVC, where the C-Cl bond is weaker (~339 kJ/mol) and chlorine is larger, providing less effective shielding.

Uses: Non-stick cookware, gaskets, seals, electrical insulation, chemical-resistant linings.

Monomers: Phenol ( $\text{C}_6\text{H}_5\text{OH}$ ) and formaldehyde ( $\text{HCHO}$ )

Polymerisation: Condensation. With excess formaldehyde and a base catalyst, cross-linked polymer forms.

Properties: Thermosetting — once hardened, it cannot be remoulded by heating (unlike the others which are thermoplastic). Hard, heat-resistant, electrically insulating.

Uses: Electrical switches, handles of utensils, radio casings, billiard balls, circuit boards.

Why This Works

The properties of each polymer directly follow from their molecular structure. Nylon’s strength comes from intermolecular hydrogen bonding between amide groups. PVC’s versatility comes from the ability to add plasticisers. Teflon’s inertness comes from the C-F bond strength. Bakelite’s rigidity comes from extensive cross-linking. Structure determines properties — this is the central theme of polymer chemistry.

NEET loves asking: “Which polymer is thermosetting?” Answer: Bakelite (and melamine). All others in this list are thermoplastic. Also frequently tested: “Nylon-6,6 is a polyamide” and “Teflon is chemically inert due to strong C-F bonds.”

Quick Comparison Table

Polymer	Monomer(s)	Type	Thermo-behaviour	Key Property
Nylon-6,6	Hexamethylenediamine + Adipic acid	Condensation	Thermoplastic	High tensile strength
PVC	Vinyl chloride	Addition	Thermoplastic	Versatile (rigid or flexible)
Teflon	Tetrafluoroethylene	Addition	Thermoplastic	Chemically inert, non-stick
Bakelite	Phenol + Formaldehyde	Condensation	Thermosetting	Hard, heat-resistant

Common Mistake

Students confuse Nylon-6 with Nylon-6,6. Nylon-6 is made from a single monomer (caprolactam) by ring-opening polymerisation. Nylon-6,6 uses two monomers (hexamethylenediamine + adipic acid) by condensation. The numbers tell you the carbon count: Nylon-6 = one monomer with 6 carbons, Nylon-6,6 = two monomers, each with 6 carbons. NEET has tested this distinction.