Polymers
Classification of Polymers
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Polymers − Large molecules having high molecular mass (103 − 107 u)
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Polymerisation − Process of formation of polymers from respective monomers
Example:
Classification of Polymers
Classification Based on Source
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Natural polymers: Found in plants and animals
Example: Proteins, starch, cellulose, resins and rubber
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Semi-synthetic polymers: Cellulose derivatives
Example: Cellulose acetate (rayon), cellulose nitrate
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Synthetic polymers: Man-made polymers
Example: Plastic (polythene), synthetic fibres (nylon 6, 6) synthetic rubbers (Buna − S)
Classification Based on Structure
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Linear Polymers: Consist of long and straight chains
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Example: High density polythene, polyvinyl chloride, etc.
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Represented as
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Branched-chain polymers: Contain linear chains having some branches
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Example: Low density polythene
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Represented as
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Cross-linked or Network polymers
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Formed from bi-functional and tri-functional polymers
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Contain strong covalent bonds between various linear polymer chains
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Example: Bakelite, melamine, etc.
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Represented as
Classification Based on Mode of Polymerisation
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Addition polymers
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Formed by the repeated addition of monomer molecules possessing double or triple bonds
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Example: Polythene (from ethene), polypropene (from propene)
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Homopolymers − Addition polymers formed by the polymerisation of a single monomeric species
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Copolymers − Formed by the addition polymerisation from two different monomers
Example: Buna-S, buna-N, etc.
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Condensation polymers
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Formed by the repeated condensation reaction between two different bi-functional or tri-functional monomeric units
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Involves elimination of small molecules such as water, alcohol, HCl, etc.
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Example: Nylon 6, 6, terylene (dacron), nylon 6, etc.
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Nylon 6, 6 − Formed by the condensation of hexamethylene diamine with adipic acid
- Ring opening polymers
- Strong acid or base catalyze the formation of these type of polymers.
- The elemental composition of monomer remains unchanged in repeating unit of polymer as in addition polymers.
- The monomers add slowly in a step growth manner to form polymers as in condensation polymers.
- Example: polymerization of caprolactum, cyclic ethers, lactones, etc.
- Nylon 6 is formed by the polymerization of caprolactam.
Classification Based on Molecular Forces
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Elastomers − Rubber-like solids with elastic properties
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Polymer chains are held together by the weakest intermolecular for…
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