Explain the term co polymerisation and give two examples.

Hint: Polymerisation can be of two types, namely homopolymerization and copolymerisation based on the number of monomers used. Try to recall a few examples of both the types of polymerisation to understand the difference. Based on the observation you can define the term copolymerisation.

Complete step by step answer:
Polymerization is a process of reacting monomer molecules together in a chemical reaction to form long polymer chains .
In chemical compounds, polymerization can occur by various types of reaction mechanisms that vary in complexity due to the functional groups present in the reactants and the steric effects that are present.
In simple polymerizations, alkenes form polymers through relatively simple free radical reactions; in contrast, reactions involving substitution at a carbonyl group require more complex synthesis due to the way in which reactants polymerize and the steric hindrance offered by neighboring groups.
 Alkanes are polymerized, with the help of strong mineral acids.
Polymerization is divided into 2 types based on the number of monomers used, namely homopolymerization and copolymerisation.
The polymerisation reaction involving a single monomer is known as homopolymerization.
Copolymerisation is the type of polymerisation reaction involving more than one type of monomer. The number of monomers involved in the reaction is usually 2.
The below diagram shows the difference between the two types of polymerisation

$\begin{align}
  & \text{Homopolymerization : } \\
 & \text{A + A + A + A }...\text{ }\to \text{ AAAA}... \\
 & \text{Copolymerisation : } \\
 & \text{A + B + A + B }...\text{ }\to \text{ ABAB}... \\
\end{align}$

Few examples of copolymers are Buna -S; Nylon 6,6; Nylon 2,6 etc.
The monomers of
-Buna -S are Styrene and 1,3 Butadiene
-Nylon 6,6 are hexamethylenediamine and Adipic acid
-Nylon 2,6 are glycine and adipic acid

Note: The two main classes of polymerisation reaction mechanisms are step-growth and chain growth polymerisation.
In step-growth polymerisation, the pairs of reactants combine at each step to form a longer polymer chain. The average molar mass increases slowly, long chains are formed only at the end of the reaction.
However, in case of chain growth polymerisation the addition of monomer to the growing chain with active centre (like free radical, cation, anion) is the chain extension step. Long chains are formed from the starting of the reaction only.