Polymers Test - 4

Buna N is an elastomeric polymer in which the polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched. So Buna N is polymer which is stretchable due to weakest intermolecular forces.

Fibres are the thread forming solids which possess high tensile strength and high modulus. The examples are polyamides (nylon 6, 6), polyesters (terylene), etc.

Thermosetting polymers are cross-linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins, etc.

There are two broad types of polymerisation reactions, i.e., the addition or chain growth polymerisation and condensation or step growth polymerisation. Polythene, teflon etc. are obtained by addition polymerisation. Polyamides, polyesters etc. are obtained by condensation polymerisation.

Natural polymers are found in plants and animals. Examples are proteins, cellulose, starch, some resins and rubber.

Polymers can be classified based on their structure as linear, branched and cross-linked polymers. They can also be classified based on mode of polymerisation as addition and condensation polymers. Also the classification can be made based on the intermolecular forces as elastomers, fibres, thermoplastic and thermosetting polymers. So polymers cannot be classified on the basis of their resistance to different agents.

Neoprene has superior resistance to vegetable and mineral oils. It is used for manufacturing conveyor belts, gaskets and hoses.

Buna N is resistant to the action of petrol, lubricating oil and organic solvents.It is used in making oil seals , tank linings etc.