# Polymers Classification > Polymers for JEE Chemistry: addition versus condensation, thermoplastic versus thermosetting, monomers of nylon and bakelite, vulcanisation and copolymers. - Canonical URL: https://prepelephant.com/topics/jee/chemistry/polymers-classification - Exam / course: JEE · Subject: Chemistry - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Polymers Classification", PrepElephant, https://prepelephant.com/topics/jee/chemistry/polymers-classification ## Direct answer Classification carries the whole chapter: addition polymers build from alkene-like monomers without losing any atoms (polythene from CH2=CH2, PVC from CH2=CHCl, Teflon from CF2=CF2), while condensation polymers expel a small molecule as they join (nylon-6,6 from hexamethylenediamine plus adipic acid losing water through amide links; Dacron from ethylene glycol plus terephthalic acid through ester links). The second axis is thermal — linear thermoplastics such as polythene soften and re-soften on heating, while cross-linked thermosettings such as bakelite (phenol plus formaldehyde) set once and never remould. Copolymers like Buna-S and Buna-N mix two monomers in one chain, natural rubber is cis-1,4-polyisoprene stiffened into usefulness by sulphur vulcanisation, and biodegradables like PHBV answer the environmental question the chapter always ends on. ## What you must remember - **Addition family with monomers:** polythene (ethene), PVC (vinyl chloride), Teflon (tetrafluoroethene, non-stick and chemically inert), polystyrene (styrene), polyacrylonitrile (acrylonitrile) — same empirical formula as monomer. - **Condensation family with links:** nylon-6,6 (amide link, monomers each carrying six carbons), Dacron or PET (ester link), bakelite (phenol-formaldehyde, -CH2- bridges at ortho and para positions, thermosetting), melamine-formaldehyde (unbreakable crockery). - **Rubber chemistry:** natural rubber is cis-1,4-polyisoprene from isoprene (2-methyl-1,3-butadiene); vulcanisation heats raw rubber with 3-5 per cent sulphur, forming cross-links that trade stickiness for strength and elasticity. - **Copolymer pair:** Buna-S (butadiene plus styrene, general-purpose synthetic rubber) and Buna-N (butadiene plus acrylonitrile, resistant to oils and petrol). - **Thermoplastic versus thermosetting mechanism:** linear or branched chains slip apart on heating; covalent cross-links refuse to melt, only char. - **LDPE versus HDPE:** peroxide-initiated high-pressure routes give branched low-density polythene; Ziegler-Natta catalysis gives linear, crystalline, high-density polythene. - **Biodegradable answers:** PHBV (a copolymer of 3-hydroxybutyric and 3-hydroxyvaleric acids, used in sutures) and nylon-2-nylon-6 (glycine plus aminocaproic acid). - **Molecular-weight honesty:** polymers are polydisperse — number-average Mn and weight-average Mw differ, with the polydispersity index Mw/Mn always at least 1. ## Reading a repeating unit backwards Take the fragment -[NH(CH2)6NHCO(CH2)4CO]n-. Read it aloud as chemistry: an amine-bearing six-carbon run and an acid-bearing four-carbon run, joined by amide (peptide-like) bonds — so the monomers must be hexamethylenediamine and adipic acid, and the polymer is nylon-6,6, water lost at every link. Now the same audit on a benzene ring carrying -CH2- bridges and hydroxyl neighbours: phenol plus formaldehyde, bakelite, thermosetting because the methylene bridges latch onto ortho and para positions in all directions, locking the network. Finish with cis-1,4-polyisoprene: the methyl-substituted double bond repeats head-to-tail, and the cis geometry keeps the chains curly and amorphous — vulcanisation's sulphur bridges then pin neighbouring coils together, which is why a rubber band snaps back. ## Where this stands in the current syllabus Straight talk: polymers was removed from the JEE Main syllabus in the 2023 rationalisation and the revised JEE Advanced syllabus dropped it too, so its marks now belong to board examinations and foundation reading rather than JEE itself — check the current NEET-UG list before investing time there as well. If you do revise it, harvest it as cheap classification marks: monomer identification, link naming (amide versus ester), and the thermoplastic-thermosetting split. The traps: calling bakelite a thermoplastic (the commonest wrong option), matching Teflon's monomer as CH2=CH2 (it is CF2=CF2), and forgetting that vulcanisation uses sulphur specifically, not any cross-linker. ## Frequently asked questions ### Which polymer is thermosetting and why? Bakelite — phenol and formaldehyde build a three-dimensional cross-linked network through methylene bridges, which cannot melt and flow again on heating. ### What are the monomers of nylon-6,6? Hexamethylenediamine and adipic acid, condensing with loss of water to form amide linkages; the 6,6 records each monomer's six carbons. ### What does vulcanisation do to rubber? Heating with 3-5 per cent sulphur forms cross-links between polyisoprene chains, converting soft, sticky rubber into a hard, elastic material with much better tensile strength. ### How do Buna-S and Buna-N differ? Both copolymerise butadiene, but Buna-S uses styrene for general-purpose rubber while Buna-N uses acrylonitrile for fuel and oil resistance. ### Which polymers biodegrade, and from what are they made? PHBV, a copolyester of 3-hydroxybutyric and 3-hydroxyvaleric acids, and nylon-2-nylon-6 from glycine and aminocaproic acid.