PYQ Vault

MHT-CET Chemistry · Introduction to Polymer Chemistry

Polymers and Their Monomers

Every named polymer is one or two monomers: isoprene for natural rubber, chloroprene for neoprene, butadiene with styrene for Buna-S and with acrylonitrile for Buna-N, acrylonitrile for PAN, styrene for thermocol, methyl methacrylate for perspex, adipic acid with hexamethylenediamine for nylon 6,6, caprolactam for nylon 6, ethylene glycol with terephthalic acid for dacron and with phthalic acid for glyptal, two 3-hydroxy acids for PHBV, phenol or urea with formaldehyde for the resins — and the linkage between them (amide, ester, or plain C–C) is what the paper asks next.

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Why this matters

29 PYQs, one HARD. Nineteen are straight monomer lookups — Buna-S, Buna-N, PAN (the wool substitute), thermocol (twice), natural rubber (twice), neoprene, novolac, dacron (three times), glyptal, PHBV (three times), nylon salt, nylon 2-nylon 6; ten are the linkage — which polymer carries –CO–NH– (urea-formaldehyde, keyed twice), which is the polyamide, which monomer pair does not give one, which carries an ester (PHBV), which carries neither (thermocol), the neoprene and natural-rubber statement questions, and the HARD cellulose-xanthate formula. Two cards.

Concept 1 of 2

Polymer to Monomer: the Table the Paper Draws From

Intuition

Group the monomers by family and the table is half memorised. The DIENE rubbers: isoprene (2-methylbuta-1,3-diene) gives natural rubber, chloroprene (2-chlorobuta-1,3-diene) gives neoprene, and buta-1,3-diene copolymerised with styrene gives Buna-S, with acrylonitrile Buna-N. The VINYL plastics: one substituted ethene each — vinyl chloride, styrene (thermocol), acrylonitrile (PAN, orlon), tetrafluoroethene (Teflon), methyl methacrylate (perspex), acrylamide. The CONDENSATION pairs: an acid with an amine (nylon 6,6, nylon 2-nylon 6), an acid with a diol (dacron, glyptal), hydroxy acids with themselves (PHBV), formaldehyde with phenol, urea or melamine.

Definition

  • Rubbers: natural rubber ← isoprene (cis-1,4); neoprene ← chloroprene (a homopolymer — 'copolymer in presence of MgO' is the false statement); Buna-S ← buta-1,3-diene + styrene; Buna-N ← buta-1,3-diene + acrylonitrile.
  • Vinyl addition polymers: PVC ← vinyl chloride; thermocol/polystyrene ← styrene; PAN (orlon, wool substitute) ← acrylonitrile CH₂=CHCN; Teflon ← CF₂=CF₂; perspex (PMMA, acrylic glass) ← methyl methacrylate; polyacrylamide ← acrylamide.
  • Polyamides: nylon 6,6 ← adipic acid + hexamethylenediamine (the nylon salt); nylon 6 ← caprolactam; nylon 2-nylon 6 ← glycine + ε-aminocaproic acid.
  • Polyesters: dacron/terylene ← ethylene glycol + terephthalic acid; glyptal ← ethylene glycol + phthalic acid; PHBV ← 3-hydroxybutanoic acid + 3-hydroxypentanoic acid.
  • Formaldehyde resins: novolac/bakelite ← phenol + HCHO; urea-formaldehyde; melamine-formaldehyde. Polycarbonate ← bisphenol A + diphenyl carbonate (or phosgene).
PolymerMonomer(s)Type
Natural rubberIsoprene (2-methylbuta-1,3-diene)Addition, homo
NeopreneChloroprene (2-chlorobuta-1,3-diene)Addition, homo
A homopolymer — the 'copolymer' statement about it is the false one.
Buna-S / Buna-NButa-1,3-diene + styrene / + acrylonitrileAddition, co
PAN (orlon)Acrylonitrile CH₂=CHCNAddition, homo — wool substitute
ThermocolStyreneAddition, homo
Perspex (PMMA)Methyl methacrylateAddition, homo
TeflonTetrafluoroethene CF₂=CF₂Addition, homo
Nylon 6,6Adipic acid + hexamethylenediamineCondensation, polyamide
Nylon 6CaprolactamRing-opening, polyamide
Nylon 2-nylon 6Glycine + ε-aminocaproic acidCondensation, biodegradable polyamide
Dacron / teryleneEthylene glycol + terephthalic acidCondensation, polyester
Phthalic acid instead of terephthalic gives glyptal.
GlyptalEthylene glycol + phthalic acidCondensation, polyester
PHBV3-Hydroxybutanoic + 3-hydroxypentanoic acidCondensation, biodegradable polyester
Novolac / bakelitePhenol + formaldehydeCondensation resin
Terephthalic (1,4) acid → dacron; phthalic (1,2) acid → glyptal.
Practice this conceptself-check · 4 quick reps

From the bank · past-year question

Example 1Introduction to Polymer ChemistryMODERATE
What are the monomers used in preparation of PHBV?

[Q96 · 23 April Shift I · 2025]

Terephthalic acid for glyptal

Both are ethylene-glycol polyesters; the para acid (terephthalic) gives dacron, the ortho acid (phthalic) gives glyptal. The options always offer both acids.
Drill 18 more on polymer to monomer: the table the paper draws from

Concept 2 of 2

The Linkage in the Repeat Unit: Amide, Ester or None

Intuition

Read the repeat unit for the bond that joins monomers. –CO–NH– means a POLYAMIDE: the nylons, urea-formaldehyde resin (–NH–CO–NH–CH₂–), and polyacrylamide carries the amide as a side group. –COO– means a POLYESTER: dacron, glyptal, PHBV, and perspex has the ester as a side group. A pure carbon backbone with no heteroatom link is an addition polymer: thermocol, polythene, PVC, Teflon; PAN's side group is a nitrile, not an amide. Two structures the paper asks by formula: cellulose xanthate (Cell–O–CS–S⁻Na⁺, the viscose intermediate) and natural rubber, a linear cis-polyisoprene made by addition.

Definition

  • –CO–NH– (amide): nylon 6 –[NH(CH₂)₅CO]–, nylon 6,6 –[CO(CH₂)₄CO–NH(CH₂)₆NH]–, nylon 2-nylon 6, urea-formaldehyde –[NH–CO–NH–CH₂]–, polyacrylamide –[CH₂–CH(CONH₂)]– (side-chain amide).
  • –COO– (ester): dacron, glyptal, PHBV, perspex –[CH₂–C(CH₃)(COOCH₃)]– (side-chain ester).
  • Neither: thermocol –[CH₂–CH(C₆H₅)]–, polythene, PVC, Teflon; PAN –[CH₂–CH(CN)]– has no amide despite the N.
  • Cellulose xanthate: Cell–OH + CS₂ + NaOH → Cell–O–CS–S⁻Na⁺ (viscose; regenerated as rayon in acid).
  • Natural rubber: linear, addition polymer of isoprene, cis C=C, soft and tacky until vulcanised. NOT butadiene + styrene (that is SBR).

Three repeat units

nylon 6: –[NH(CH2)5CO]n–;urea-formaldehyde: –[NH–CO–NH–CH2]n–;thermocol: –[CH2–CH(C6H5)]n–\text{nylon 6: } \text{–[NH(CH}_2)_5\text{CO]}_n\text{–};\quad \text{urea-formaldehyde: } \text{–[NH–CO–NH–CH}_2]_n\text{–};\quad \text{thermocol: } \text{–[CH}_2\text{–CH(C}_6\text{H}_5)]_n\text{–}

Worked example

A polymer's repeat unit is –[O–CH(CH₃)–CH₂–CO]–. Name the linkage, the monomer and the class of polymer.
Practice this conceptself-check · 4 quick reps

From the bank · past-year question

Example 2Introduction to Polymer ChemistryHARD
If Cell-OH represents formula of cellulose, identify the formula of cellulose xanthate from following.

[Q79 · 3rd May Shift 2 · 2023]

PAN as a polyamide

The nitrogen in polyacrylonitrile is a nitrile, –C≡N; there is no carbonyl beside it. Among PAN, nylon 6, nylon 6,6 and nylon 2,6 it is the one WITHOUT the amide linkage.
Drill 9 more on the linkage in the repeat unit: amide, ester or none

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)

  • The Linkage in the Repeat Unit: Amide, Ester or None

    Three repeat units

    nylon 6: –[NH(CH2)5CO]n–;urea-formaldehyde: –[NH–CO–NH–CH2]n–;thermocol: –[CH2–CH(C6H5)]n–\text{nylon 6: } \text{–[NH(CH}_2)_5\text{CO]}_n\text{–};\quad \text{urea-formaldehyde: } \text{–[NH–CO–NH–CH}_2]_n\text{–};\quad \text{thermocol: } \text{–[CH}_2\text{–CH(C}_6\text{H}_5)]_n\text{–}

Reference tables (1)

Polymer to Monomer: the Table the Paper Draws From14 rows
PolymerMonomer(s)Type
Natural rubberIsoprene (2-methylbuta-1,3-diene)Addition, homo
NeopreneChloroprene (2-chlorobuta-1,3-diene)Addition, homo
A homopolymer — the 'copolymer' statement about it is the false one.
Buna-S / Buna-NButa-1,3-diene + styrene / + acrylonitrileAddition, co
PAN (orlon)Acrylonitrile CH₂=CHCNAddition, homo — wool substitute
ThermocolStyreneAddition, homo
Perspex (PMMA)Methyl methacrylateAddition, homo
TeflonTetrafluoroethene CF₂=CF₂Addition, homo
Nylon 6,6Adipic acid + hexamethylenediamineCondensation, polyamide
Nylon 6CaprolactamRing-opening, polyamide
Nylon 2-nylon 6Glycine + ε-aminocaproic acidCondensation, biodegradable polyamide
Dacron / teryleneEthylene glycol + terephthalic acidCondensation, polyester
Phthalic acid instead of terephthalic gives glyptal.
GlyptalEthylene glycol + phthalic acidCondensation, polyester
PHBV3-Hydroxybutanoic + 3-hydroxypentanoic acidCondensation, biodegradable polyester
Novolac / bakelitePhenol + formaldehydeCondensation resin
Terephthalic (1,4) acid → dacron; phthalic (1,2) acid → glyptal.

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