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Polymers

Classification of Polymers

  • Polymers − Large molecules having high molecular mass (103 − 107 u)

  • Polymerisation − Process of formation of polymers from respective monomers

Example:

Classification of Polymers

Classification Based on Source

  • Natural polymers: Found in plants and animals

Example: Proteins, starch, cellulose, resins and rubber

  • Semi-synthetic polymers: Cellulose derivatives

Example: Cellulose acetate (rayon), cellulose nitrate

  • Synthetic polymers: Man-made polymers

Example: Plastic (polythene), synthetic fibres (nylon 6, 6) synthetic rubbers (Buna − S)

Classification Based on Structure

  • Linear Polymers: Consist of long and straight chains

  • Example: High density polythene, polyvinyl chloride, etc.

  • Represented as

  • Branched-chain polymers: Contain linear chains having some branches

  • Example: Low density polythene

  • Represented as

  • Cross-linked or Network polymers

  • Formed from bi-functional and tri-functional polymers

  • Contain strong covalent bonds between various linear polymer chains

  • Example: Bakelite, melamine, etc.

  • Represented as

Classification Based on Mode of Polymerisation

  • Addition polymers

  • Formed by the repeated addition of monomer molecules possessing double or triple bonds

  • Example: Polythene (from ethene), polypropene (from propene)

  • Homopolymers − Addition polymers formed by the polymerisation of a single monomeric species

  • Copolymers − Formed by the addition polymerisation from two different monomers

Example: Buna-S, buna-N, etc.

  • Condensation polymers

  • Formed by the repeated condensation reaction between two different bi-functional or tri-functional monomeric units

  • Involves elimination of small molecules such as water, alcohol, HCl, etc.

  • Example: Nylon 6, 6, terylene (dacron), nylon 6, etc.

  • Nylon 6, 6 − Formed by the condensation of hexamethylene diamine with adipic acid

Classification Based on Molecular Forces

  • Elastomers − Rubber-like solids with elastic properties

  • Polymer chains are held together by the weakest intermolecular forces.

  • Weak binding forces permit the polymer to be stretched.

  • Cross-links’ are …

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