(N/A) Copolymerization is a polymerization reaction in which a mixture of more than one monomeric species is allowed to polymerize and form a copolymer.
The copolymer can be made not only by chain growth polymerization but by step growth polymerization also.
It contains multiple units of each monomer used in the same polymeric chain.
For example,a mixture of $1,3$-butadiene and styrene can form a copolymer as shown below:
$nCH_2=CH-CH=CH_2 + nC_6H_5CH=CH_2 \rightarrow -[CH_2-CH=CH-CH_2-CH(C_6H_5)-CH_2]_n-$
Copolymers have properties quite different from homopolymers.
For example,butadiene-styrene copolymer is quite tough and is a good substitute for natural rubber.
It is used for the manufacture of autotyres,floor tiles,footwear components,cable insulation,etc.