Elastomers

1) Vulcanization of Rubber: Vulcanization is a process where natural rubber is boiled with sulphur to make it harder.

2) Thermosetting Polymer: They are made from relatively low molecular mass semi-fluid polymers which on heating become hard and infusible. This is due to extensive cross-linking between various chains. They have three dimensional network of bonds. Thermosetting polymer is irreversible. It cannot be melt again. E.g. Bakelite, melamine.

3) Thermoplastic Polymer: Thermoplastic polymers soften on heating and harden on cooling. There is no cross-linking between the chains. Thus, they undergo reversible change when heated and cooled. E.g. PVC, Polyethylene, polypropylene, Polystyrene, etc.

4) Elastomers (Rubber/ Rubber like substance): In these the chains are held by weakest intermolecular forces, due to these weak forces, the polymers can be stretched. A few cross-links present between the chains permit the polymer to attain its original form when the forces ceases. E.g. vulcanized rubber, Buna-N, neoprene, Buna-S, etc.

5) Fibres: They possess high tensile strength and high modulus due to strong intermolecular forces like H-bonding. For examples, Nylon-66, Nylon-6, Dacron/ Terylene.

6) Buna-S (Styrene Butadiene Rubber): It is prepared by the polymerization of butadiene and styrene in the presence of sodium metal.

 n CH₂=CH- CH=CH₂  +  x CH(C₆H₅)=CH₂  ——->  (-CH₂-CH=CH-CH₂)_n–(CH(C₆H₅)-CH₂)_x

                   1,3-Butadiene               Styrene                                      Buna-S

7) Buna-N: It is prepared by the polymerization of butadiene and acrylonitrile in the presence of sodium metal.

 n CH₂=CH- CH=CH₂  +  x CH(CN)=CH₂  ——->  (-CH₂-CH=CH-CH₂)_n–(CH(CN)-CH₂)_x

              1,3-Butadiene               Acrylonitrile                                       Buna-N

Uses:  For making tyres, floor tiles, foot wear component, cable insulation / for making oil seals, tank linings to keep petrol.

8) PVC: By polymerization of vinyl chloride (CH₂=CH-Cl) in presence of peroxide.

9) Teflon (Polytetrafluoroethylene, PTFE): It is prepared by the polymerisation of tetrafluroethylene.

nCF₂=CF₂    ——->  (CF₂-CF₂)n

Uses: It is used for making oil seal, gaskets, non-sticky pan.

10) Polyacrylonitrile (PAN): It is prepared by the polymerisation of acryonitrile.

n CH(CN)=CH₂   ——–>   -(CH(CN) –CH₂)_n

                                              Acrylonitrile                          Polyacrylonitrile

Uses: It is used as a substitute of wool, for making cloths, carpets and Blankets.

11) Polystyrene: It is prepared by the polymerisation of styrene.

nCH(C₆H₅)=CH₂  ———>   –(CH(C₆H₅)-CH₂)_n

Uses: It is used to make hot drink cups, toys, radio-TV bodies, etc.