POLYMERS

POLYMERS

1. Very large molecules having high molecular masses

2. SUB CATEGORIES

   • Natural Polymers
     • Found in proteins, cellulose, resins and starch
   • Semi-synthetic Polymers
     • Cellulose derivatives as cellulose acetate and cellulose nitrate
   • Synthetic Polymers
     • Used in daily life such as the plastic, synthetic fibres and synthethic rubbers

3. POLYMERS STRUCTURES

   • Linear Polymers
     • Long and straight chains (high density polythene, polyvinyl chloride)
   • Branched Chain Polymers
     • Linear chains with branches (low density polythene)
   • Network Polymers
     • Bi and trifunctional monomers with strong covalent bonds between linear chains (bakelite, melamine)

4. MODE OF POLYMERISATION

   • Condensation Polymers
     • Formed by repeated condensation between bi or trifunctional monomeric units. Elimination of small molecules (terylene, nylon 6,6, nylon 6)
   • Addition Polymers
     • Formed by repeated addition of monomer molecules possessing double or triple bonds (polythene from ethene, polypropene from propene) Single monomeric = homopolymers & 2+ monomers = copolymers

5. MOLECULAR FORCES

   • Elastomer
     • Solids with elastic properties
     • Chains are held together by the weakest intermolecular forces.
     • Crosslinks are in between the chains, which helps the polymerretract to its original position
   • Fibres
     • Thread forming solids that possess high tensile strenght and high modulus
     • Strong intermolecular forces
     • Close packing of chain
   • Thermoplastic Polymers
     • Cross-linked or heavily branched molecules
     • Undergo extensive cross-linking in molds and become infusible on heat
     • Can not be reused in any way
   • Thermosetting polymers
     • Linear branched long chain molecules
     • Softening on heating and hardening on cooling
     • Intermolecular forces of attraction between elastomers and fibres

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