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MHT-CET Chemistry · Teaching notes

Introduction to Polymer Chemistry — MHT-CET Chemistry

Polymers is about two questions a paper in MHT-CET Chemistry and almost never HARD — one of its past-year questions in eighty-six. It is a chapter of named pairs: a polymer and its class (fibre, elastomer, thermoplastic, thermoset; homo- or copolymer), a polymer and its monomers, a polymer and the linkage that holds it, and a polymer and the household article it is made into. The only reasoning is in the polymerisation method — addition, condensation or ring-opening — and in telling LDPE from HDPE. Four pages in the book's order. Every PYQ is tagged.

Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.

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Subtopic notes

PYQ weightage by concept

7 concepts · 86 PYQs — where the marks actually sit, so you know what to drill first

Classification of Polymers22 PYQs · 26%
ConceptPYQsShare
By Source, by Chain Structure, by Number of Monomers1113%
Elastomer, Fibre, Thermoplastic, Thermosetting: Ranked by Intermolecular Force1113%
Polymerisation Methods: Addition, Condensation, Ring-Opening9 PYQs · 10%
ConceptPYQsShare
Which Method Makes Which Polymer910%
Polymers and Their Monomers29 PYQs · 34%
ConceptPYQsShare
Polymer to Monomer: the Table the Paper Draws From1922%
The Linkage in the Repeat Unit: Amide, Ester or None1012%
Properties and Applications of Polymers26 PYQs · 30%
ConceptPYQsShare
Which Polymer Makes Which Article1922%
LDPE against HDPE, and Vulcanisation78%

Formula & revision sheet

4 formulas · 3 reference tables · 7 gotchas across all subtopics — the exam-eve cheat-sheet

Classification of Polymers

Formulas (1)

  • By Source, by Chain Structure, by Number of Monomers · Three axes
    source: natural / semisynthetic / synthetic;chain: linear / branched / cross-linked;monomers: homo- / co-polymer\text{source: natural / semisynthetic / synthetic};\quad \text{chain: linear / branched / cross-linked};\quad \text{monomers: homo- / co-polymer}

Reference tables (1)

Elastomer, Fibre, Thermoplastic, Thermosetting: Ranked by Intermolecular Force4 rows
ClassIntermolecular forceHeatingExamples
ElastomerWeakest (a few cross-links)Stretch and recoverNatural rubber, Buna-S, Buna-N, neoprene
ThermoplasticIntermediateSoftens, remouldablePolythene, PVC, polystyrene, Teflon, PMMA
Thermoplastics have NO extensive cross-linking.
ThermosettingCross-linked networkSets once, cannot remeltBakelite, urea-formaldehyde, melamine-formaldehyde
FibreStrongest (H-bond / dipole)High tensile strength, drawn to threadNylon 6, nylon 6,6, terylene, PAN
The force ranking is elastomer < thermoplastic < fibre; thermosets are a structure, not a force level.

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Polymerisation Methods: Addition, Condensation, Ring-Opening

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)

Polymers and Their Monomers

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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Properties and Applications of Polymers

Formulas (1)

  • LDPE against HDPE, and Vulcanisation · Two polythenes
    LDPE: 103–2×103 atm, O2/peroxide, branched;HDPE: 6–7 atm, Ziegler–Natta, linear\text{LDPE: } 10^3\text{–}2\times10^3\ \text{atm, O}_2/\text{peroxide, branched};\quad \text{HDPE: } 6\text{–}7\ \text{atm, Ziegler–Natta, linear}

Reference tables (1)

Which Polymer Makes Which Article13 rows
ArticlePolymerWhy
Water pipes, floor tilesPVCRigid, chemically resistant
Disposable cups and platesPolystyreneCheap, foamable; leaches styrene
Drinking strawsPolypropyleneRigid, heat-resistant
Toys, bucketsHDPETough, crystalline
Tyre cordsNylon 6High tensile strength
Nylon 6 → tyre cords; nylon 6,6 → bristles and sutures.
Brush bristles, surgical suturesNylon 6,6Stiff, strong polyamide
Wool substitutePolyacrylonitrileSoft, warm fibre
TerycotDacron + cottonWrinkle-free blend
Oil seals, gasketsTeflonInert, low friction
Rubber belts, shoe solesBuna-NOil- and abrasion-resistant
PaintsGlyptalAlkyd resin
LCD screensPerspexTransparent PMMA
Plastic dinner wareMelamine-formaldehydeHard thermoset
The two nylons split the jobs: 6 for tyre cords, 6,6 for bristles and sutures.

Watch out for (2)