Classification Of Polymers

Concept: Natural rubber is cis-1,4-polyisoprene, formed by the polymerization of isoprene (2-methyl-1,3-butadiene).

Step 1: Structure of isoprene. Isoprene has the structure: It is a conjugated diene with double bonds at positions 1 and 3.

Step 2: Type of polymerization. During polymerization, isoprene undergoes 1,4-addition. The double bonds at positions 1 and 4 (numbering from one end) open up, and monomers link together through carbons 1 and 4. One double bond remains in each monomer unit (between carbons 2 and 3).

Step 3: Structure of natural rubber. This is cis-1,4-polyisoprene.

Step 4: Why not other options?
• (B) 1,2 addition — would give a different polymer structure (not natural rubber).
• (C) 1,3 addition — does not occur in diene polymerization.
• (D) both double bonds convert into single bonds — false, one double bond remains in each monomer unit.

Concept: PTFE (Polytetrafluoroethylene), commonly known as Teflon, has unique properties that make it suitable for both lubrication and electrical insulation.

Step 1: Properties of PTFE.
• Very low coefficient of friction (one of the lowest of any solid) → excellent dry lubricant.
• High electrical resistivity → excellent electrical insulator.
• Chemically inert, high thermal stability, non-stick.

Step 2: Check other options.
• (A) SBR (Styrene-Butadiene Rubber) → used in tires, not a lubricant or good insulator.
• (B) PVC (Polyvinyl chloride) → good insulator but not used as a lubricant.
• (C) PTFE → satisfies both conditions.
• (D) PAN (Polyacrylonitrile) → used in fibers (Acrilan), not as lubricant.

Concept: Acrilan is polyacrylonitrile (PAN).

Step 1: Monomer.

Step 2: Polymer structure.

Step 3: Identification. Option (D) matches the polyacrylonitrile structure.

Concept:
• Polystyrene formed by addition polymerization chain growth
• Dacron (polyester) formed by condensation step growth

Step 1: Polystyrene.
Addition polymer chain growth

Step 2: Dacron.
Condensation polymer step growth

Step 3: Final answer.
Chain growth, Step growth