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Thursday, 16 March 2017

Polymer I

1. Polymer: 
It is a very large molecule having molecular mass 103 - 107 g mol-1 They are formed by joining together repeating structural units.

2. Classification of Polymers:
(a) Based On Source:
(i) Natural:
     Found in plants and animals, e.g. Proteins, cellulose, natural rubber, silk, wool.

(ii) Synthetic: 
      Man-made e.g. Nylon, polyster, neoprene, Bakelite, Teflon, PVC, polystyrene.

(b) Based On Structure:
(i) Linear Polymers:
     This consist of long and straight chain repeating units 
     e.g. Polythene (HDPE), PVC, nylon, polyester.

(ii) Branched Polymers: 
      This contain linear chains having some branches 
       e.g. amylopectin, glycogen etc.

(iii) Cross Linked Polymers: 
       Strong covalent bonds are present between various linear polymer chains.
       E.g. Bakelite, urea- formaldehyde polymer, melamine, formaldehyde polymer etc.

(c) Based On Mode Of Polymerization:
(i) Addition Polymers: 
     These are formed by the repeated addition of monomer molecules possessing multiple bonds.
e.g., polythene, polypropene, polystyrene, PMMA (polymethyl metha crylate)

(ii) Condensation Polymers: 
      These are formed by the repeated condensation reaction of different bifunctional or trifunctional monomers, with the elimination of small molecules like water,HCL,NH3, alcohol etc. 
e.g. Bakelite,nylon,polyster,urea- formaldehyde resin.

(d) Based On Molecular Forces:
(i) Elastomers: 
      Forces of interaction between polymer chains is weakest, e.g. natural rubber, neoprene, vulcanized rubber.

(ii) Fibers: 
      Strong hydrogen bonds are present between the polymer chains. They have high tensile strength.
e.g., nylon.polyster, silk, wool, orlon, rayon etc.

(iii) Thermoplastics: 
       They are linear/slightly branched chains molecules capable of repeated softening on heating and hardening on cooling.
e.g., polythene,PVC, polystrene, polypropene.

(iv) Thermosetting Plastics: 
       They are cross-linked or heavily branched molecules, which on heating undergo extensive cross-linkages and become infusible.
e.g., bakelite,urea formaldehyde resin.

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