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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

9 PYQs, none HARD. 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

Intuition

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.
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From the bank · past-year question

Example 1Introduction to Polymer ChemistryMODERATE
Which from following polymers is NOT obtained by addition polymerisation method?

[Q84 · 4th May Shift 1 · 2023]

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

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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)

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