# Polymers > Addition and condensation polymerisation, thermoplastics and thermosets, vulcanisation of rubber and biodegradable polymers — NEET-UG Chemistry notes. - Canonical URL: https://prepelephant.com/topics/neet-ug/chemistry/polymers-ncert - Exam / course: NEET-UG · 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", PrepElephant, https://prepelephant.com/topics/neet-ug/chemistry/polymers-ncert ## Direct answer Nylon 6,6, made from adipic acid and hexamethylenediamine, was the first fully synthetic fibre, and its name encodes the recipe: six carbon atoms in each monomer, joined by amide bonds through condensation (step-growth) polymerisation. Addition (chain-growth) polymers — polythene, PVC, Teflon — simply add monomer units without losing anything. The classification axes NEET tests are source (natural, semi-synthetic, synthetic), growth mode, and intermolecular force: elastomers stretch, fibres hang together through strong hydrogen bonding, thermoplastics remould on heating and thermosets such as bakelite never do. Natural rubber is cis-1,4-polyisoprene, and vulcanisation with sulphur cross-links it into the elastic material Goodyear discovered in 1839. ## What you must remember - Polythene: LDPE from peroxide-initiated high pressure (350–570 K), HDPE via a Ziegler-Natta catalyst at low pressure — tougher, used for buckets and pipes. - Teflon (PTFE) is chemically inert and heat-resistant — non-stick cookware; PAN fibres (Orlon) substitute the nitrile group. - Condensation classics: nylon 6,6 and nylon 6 (from caprolactam); terylene/Dacron (PET) from ethylene glycol and terephthalic acid/ester. - Bakelite (phenol + formaldehyde) forms novolac first, then cross-links irreversibly — the standard thermoset, used in switches. - Buna-S (butadiene + styrene) and Buna-N (butadiene + acrylonitrile) are synthetic rubbers; neoprene (polychloroprene) resists oils. - Gutta-percha is trans-1,4-polyisoprene — hard and brittle where natural rubber's cis form is soft and elastic. - Vulcanisation with about 5 per cent sulphur makes elastic rubber; more sulphur gives hard ebonite. - Biodegradable examples NCERT lists: PHBV (used in packaging and orthopaedic devices) and nylon-2-nylon-6, from glycine and aminocaproic acid. ## Classification by force, reasoned Ask why nylon makes fibres while polyisoprene makes elastic bands, and the answer is chain architecture plus intermolecular force. Nylon 6,6 chains are linear and bristle with amide groups, so adjacent chains hydrogen-bond tightly along their length — exactly like silk — pulling chains into close, crystalline alignment; that rigidity under tension defines a fibre. Polyethylene chains attract only through dispersion forces, slide past each other when warmed, and remould — a thermoplastic. Bakelite's phenol-formaldehyde network reacts until chains are covalently cross-linked in three dimensions; heat cannot let it flow, only char, which is why thermosets are moulded once during synthesis. Natural rubber's cis-polyisoprene coils are compact and weakly attracting, so chains uncoil under pull and snap back — an elastomer — but slide permanently past each other unless vulcanisation's sulphur bridges restrain them. Every classification question — "which is an elastomer/fibre/thermoset" — is really asking which intermolecular force and architecture the polymer has, and naming the monomers is half the marks. ## Name games: monomers and numbers Monomer-to-polymer matching tables are the format, and the confusions are predictable: Buna-S versus Buna-N (styrene versus acrylonitrile as co-monomer with butadiene), terylene versus nylon (ester versus amide linkage), and the two polythenes' preparation conditions. Second, "nylon 6" and "nylon 6,6" are different substances — caprolactam versus the diamine-diacid pair — and options bank on the blur. Third, the vulcanisation detail: sulphur forms cross-links at the double-bond sites, and the amount matters — about 5 per cent gives the rubber of tyres, much more gives ebonite. Fourth, biodegradability questions: PHBV and nylon-2-nylon-6 are the two NCERT-named biodegradable polymers, and ester/amine linkages susceptible to hydrolysis are the reasoning behind them. Finally, molecular mass has two averages — number-average Mn and weight-average Mw — with polydispersity index Mw/Mn always ≥ 1; claiming a polymer has a single molar mass is the distracter. ## Frequently asked questions ### What do the numbers in nylon 6,6 stand for? Six carbon atoms in hexamethylenediamine and six in adipic acid; nylon 6, from caprolactam alone, has only one six. ### Why is bakelite a thermosetting polymer? Its phenol-formaldehyde chains cross-link covalently during curing, forming a three-dimensional network that cannot be softened and remoulded by heat. ### What is vulcanisation? Heating natural rubber with sulphur so cross-links form between chains, converting sticky raw rubber into a strong, elastic material — Charles Goodyear, 1839. ### Which polymers does NCERT list as biodegradable? PHBV (poly-β-hydroxybutyrate-co-β-hydroxyvalerate) and nylon-2-nylon-6, both degradable through hydrolysable linkages. ### Why is gutta-percha hard while natural rubber is soft? Gutta-percha is trans-1,4-polyisoprene whose zig-zag chains pack closely; the cis geometry of rubber keeps chains kinked and loosely attracting.