CBSE Class 12 Chemistry Polymers Board Exam Notes

KEY POINTS

Polymer:

It is a very large molecule having high molecular mass (103 ‐ 107 u). They are formed by joining of repeating structural units on large scale.
Copolymer is derived from more than one species of monomer. Copolymer is fromed by copolymerization of two monomer species.
 
Classification of polymers:
Based on Source
 
(i) Natural: Found in plants and animals, e.g. proteins, cellulose, natural rubber,.
 
(ii) Synthetic: Man‐made e.g. nylon, polyester, neoprene, Bakelite, Teflon, PV.C, Semi‐synthetic: Cellulose derivatives as cellulose acetate and cellulose nitrate.
 
(iii) Based on structure:

Linear polymers: This consist of long and straight chain repeating units. e.g. polythene (HDPE), PVC, nylon, polyester.
Branched polymers: This contain linear chains having some branches e.g. amylopectin.
 
Cross linked polymers: Strong covalent bonds are present between various linear polymer chains.
e.g Bakelite, urea‐formaldehyde polymer, melamine etc.
 
Based on molecular forces:

Elastomers: Forces of interaction between polymer chains is weakest, e.g. Buna ‐S , Buna‐ N, neoprene etc.
 
Fibers: Strong hydrogen bonds are present between the polymer chains. They have high tensile strength e.g., nylon, polyester, silk, wool, orlon, rayon etc.
 
Thermoplastics: They are linear/slightly branched chain molecules capable of repeatedly softening on heating and hardening on cooling, e.g. polythene, PVC, polystyrene, etc.
 
Thermosetting Plastics: They are coss‐linked or heavily branched molecules, which on heating undergo extensive cross‐linkages and become infusible, e.g, bakelite, urea- formaldehyde resin etc.
 
 
POLYMERS AT A GLANCE


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