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MHT-CET Chemistry · Formula sheet

Introduction to Polymer Chemistry formulas

4 formulas, 3 reference tables and 7 common traps for MHT-CET Chemistry Introduction to Polymer Chemistry, grouped by subtopic.

Full notes with worked examples

Classification of Polymers

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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}

Elastomer, Fibre, Thermoplastic, Thermosetting: Ranked by Intermolecular Force

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.

Common traps

Nylon 6,6 as the copolymer

It is made from two monomers, and the paper still keys Buna-S when both are offered. Reserve nylon 6,6 for 'polyamide', 'condensation' and 'fibre'.

Neoprene as a fibre, bakelite as a thermoplastic

Anything called a rubber (Buna, neoprene) is an elastomer; anything ending in '-formaldehyde' or called bakelite is thermosetting. Fibres are the nylons, polyesters and PAN.

Polymerisation Methods: Addition, Condensation, Ring-Opening

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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}

Common traps

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.

Polymers and Their Monomers

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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{–}

Polymer to Monomer: the Table the Paper Draws From

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.

Common traps

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.

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.

Properties and Applications of Polymers

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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}

Which Polymer Makes Which Article

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.

Common traps

Reading '6–7 atm' as LDPE

Low density needs HIGH pressure; the low-pressure Ziegler–Natta process gives the HIGH-density polymer. The paper plants each pressure under the wrong polymer.

Nylon 6 for bristles

Both nylons are strong, but the paper's split is fixed: nylon 6 → tyre cords, nylon 6,6 → bristles and sutures. Swapping them is the standard wrong answer.

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