When two different types of monomers are joined in the same polymeric chain, the polymer is called a copolymer. When the two monomers are arranged in an alternating fashion, the polymer is called an alternating copolymer.
A – B – A – B – A – B – A – B – A – B – A – Alternating copolymer.
In the random copolymer, the two monomers may follow in any order.
– A – A – B – A – B – B – A – B – Random polymer.

In a block copolymer, the same types of monomers are grouped together and the different types of monomers are grouped together.
A – A – A – A – B – B – B – B – B – Block copolymer.
When chains of a polymer made of monomer B are grafted on to a polymeric chain of monomer A, graft copolymer is obtained.
Example: Nylon–66 and Buna–S rubber are copolymers.

Buna rubbers:
Synthetic rubbers obtained from butadiene are called buna rubbers. Buna–S is a copolymer of a mixture of 1,3 – Butadiene and styrene in the ratio of 3 : 1 in the presence of sodium (which is polymerizing agent) gives styrene – butadiene copolymer (styrene – butadiene rubber) or Buna – S. The name Buna – S is made up of Bu which indicates 1,3 – Butadiene, NA is for Sodium (Na) and S indicates Styrene.

Buna–S rubber is very tough and a good substitute for natural rubber. It possesses high abrasion resistance. It has high load bearing capacity. It is used for manufacturing automobile tyres. It is used for making floor tiles, footwear components, cable insulation etc.

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