JEE Main 2021 · 31 August · evening · Single correct · +4 / −1
Which among the following is not a polyester?
- (a) Novolac
- (b) PHBV
- (c) Dacron
- (d) Glyptal
Answer and solution
Answer (a) Novolac
Solution
Chemistry ma’am · 3 steps
Look at the link between monomers: a polyester needs -COO⁻, and novolac has only -CH₂⁻ bridges.
- What makes a polyester. A polyester forms when an -OH group reacts with a -COOH group and water is lost. This repeats along the chain, so the units are joined by ester links, -COO⁻.
Polymer Monomers Link between units Novolac phenol + methanal (HCHO) methylene bridge -CH₂⁻, no ester PHBV 3-hydroxybutanoic acid + 3-hydroxypentanoic acid ester -COO⁻ Dacron ethane-1,2-diol + terephthalic acid ester -COO⁻ Glyptal ethane-1,2-diol + phthalic acid ester -COO⁻ - Why novolac differs. In novolac, methanal joins phenol rings at their ortho and para positions through -CH₂⁻ groups. Neither monomer has a -COOH group, so no ester link can form. Novolac is a phenol-formaldehyde resin, the linear form that cross-links to give Bakelite.
- So. PHBV, Dacron and Glyptal are all polyesters. Novolac, option (a), is not.
The idea to keep. To classify a condensation polymer, find the link between units: -COO⁻ means polyester, -CONH⁻ means polyamide, and -CH₂⁻ bridges between rings mean a phenol-formaldehyde type resin.
Answer from the NTA final answer key. Solution by PrepWiser.