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MHT-CET Chemistry · Introduction to Polymer Chemistry

Polymerisation Methods: Addition, Condensation, Ring-Opening

Addition (chain-growth) polymerisation joins C=C monomers with nothing lost, usually through a free radical from a peroxide initiator; condensation (step-growth) joins two functional groups with loss of a small molecule such as water; ring-opening polymerisation unrolls a cyclic monomer — caprolactam to nylon 6 — with nothing lost and no C=C.

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Why this matters

14 PYQs, none HARD. Of the nine set from 2021 to 2025, six ask which listed polymer is made by which method — Teflon and PAN by addition (Teflon from C₂F₄; PAN needs a peroxide initiator), nylon 6,6 and dacron by condensation, nylon 6 by ring-opening (three times, once from drawn structures); three are the 'NOT addition' and monomer-pair forms of the same question. One card.

Concept 1 of 1: Which Method Makes Which Polymer

Look at the monomer. A C=C monomer polymerises by ADDITION: a peroxide initiator makes a radical that opens double bond after double bond, nothing is lost, and the repeat unit has the monomer's formula (ethene → polythene, CF₂=CF₂ → Teflon, CH₂=CHCN → PAN, CH₂=CHCl → PVC, styrene → polystyrene). Two bifunctional monomers polymerise by CONDENSATION, losing water (or HCl) at every link: a diacid and a diamine give the polyamide nylon 6,6, a diacid and a diol the polyester dacron, phenol or urea with formaldehyde the resins. A cyclic amide simply opens: caprolactam → nylon 6 by RING-OPENING, no small molecule lost, though the paper's key files it under condensation.

Definition

  • Addition (chain-growth): monomer has C=C; free-radical mechanism, peroxide (or O₂) initiator; no by-product. Polythene, PVC, Teflon (from C₂F₄), polyacrylonitrile, polystyrene, PMMA, natural and synthetic rubbers.
  • Condensation (step-growth): two functional groups per monomer, small molecule eliminated. Nylon 6,6 (hexamethylenediamine + adipic acid, −H₂O), dacron/terylene (ethylene glycol + terephthalic acid — a dihydric alcohol + an aromatic dicarboxylic acid), glyptal, bakelite, urea- and melamine-formaldehyde, PHBV, polycarbonate.
  • Ring-opening: nylon 6 from caprolactam (a cyclic amide); no by-product. Asked as 'ring-opening' and keyed 'NOT addition'.
  • Polyamide test for a monomer pair: an acid + an amine (or an amino acid) gives –CO–NH–; two hydroxy acids (3-hydroxybutanoic + 3-hydroxypentanoic) give a polyESTER, not a polyamide.
  • Perylene/glyptal, nylons and bakelite need no initiator; a peroxide is the mark of an addition polymer.

Addition versus condensation

n CF2=CF2→peroxide–(CF2–CF2)n–;n HOOC(CH2)4COOH+n H2N(CH2)6NH2→nylon 6,6+2n H2On\,\text{CF}_2\text{=CF}_2 \xrightarrow{\text{peroxide}} \text{–(CF}_2\text{–CF}_2\text{)}_n\text{–};\qquad n\,\text{HOOC(CH}_2)_4\text{COOH} + n\,\text{H}_2\text{N(CH}_2)_6\text{NH}_2 \to \text{nylon 6,6} + 2n\,\text{H}_2\text{O}

Worked example

Classify the method for each: PMMA from methyl methacrylate; glyptal from ethylene glycol and phthalic acid; nylon 6 from caprolactam.
Practise this conceptself-check · 4 quick reps

The same idea in a real exam question:

MHT-CET · 2023 · 4th May Shift 1 · Q84Moderate

Example 1 · Introduction to Polymer Chemistry · Polymerization Methods

Which from following polymers is NOT obtained by addition polymerisation method?

Nylon 6 as an addition polymer because nothing is lost

No by-product, but no C=C either — caprolactam opens its ring. The paper classes nylon 6 with the condensation polymers and keys it as the one NOT made by addition.
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Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (1)

  • Which Method Makes Which Polymer

    Addition versus condensation

    n CF2=CF2→peroxide–(CF2–CF2)n–;n HOOC(CH2)4COOH+n H2N(CH2)6NH2→nylon 6,6+2n H2On\,\text{CF}_2\text{=CF}_2 \xrightarrow{\text{peroxide}} \text{–(CF}_2\text{–CF}_2\text{)}_n\text{–};\qquad n\,\text{HOOC(CH}_2)_4\text{COOH} + n\,\text{H}_2\text{N(CH}_2)_6\text{NH}_2 \to \text{nylon 6,6} + 2n\,\text{H}_2\text{O}

Watch out for (1)

Test yourself on Introduction to Polymer Chemistry

20 past MHT-CET questions from this chapter, timed at 18 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.

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