JEE Main 2021 · 20 July · evening · Single correct · +4 / −1
Bakelite is a cross-linked polymer of formaldehyde and :
- (a) PHBV
- (b) Buna-S
- (c) Novolac
- (d) Dacron
Answer and solution
Answer (c) Novolac
Solution
Chemistry ma’am · 3 steps
Bakelite is built in two stages: phenol and HCHO first give novolac, and more HCHO cross-links it.
- Stage one. Phenol and formaldehyde condense with acid or base to give o- and p-hydroxymethylphenols. These link up through -CH₂⁻ bridges into a linear polymer called novolac.
- Stage two. Novolac is heated with more formaldehyde. New -CH₂⁻ bridges form between the chains, giving a rigid three-dimensional network that does not melt. This is Bakelite, a thermosetting polymer.
Option Made from What it is PHBV 3-hydroxybutanoic acid + 3-hydroxypentanoic acid biodegradable polyester Buna-S 1,3-butadiene + styrene synthetic rubber (addition copolymer) Novolac phenol + formaldehyde linear chain that cross-links into Bakelite Dacron ethylene glycol + terephthalic acid polyester fibre - So. Bakelite is the cross-linked product of formaldehyde and novolac, option (c).
The idea to keep. Phenol + HCHO gives linear novolac. Novolac + more HCHO, on heating, gives cross-linked Bakelite. Linear first, network second.
Answer from the NTA final answer key. Solution by PrepWiser.