Which method is used to prepare copolymers?

Case: Read the passage and answer the following questions

There are two broad types of polymerisation reactions, i.e., the addition or chain growth polymerisation and condensation or step-growth polymerisation. In chain-growth polymerisation, the molecules of the same monomer or different monomers add together on a large scale to form a polymer. This type of polymerisation is explained free radicle mechanism. Some important addition polymers are polythene and teflon. Condensation polymerisation or step-growth polymerisation generally involves a repetitive condensation reaction between two bi-functional or trifunctional monomeric units. Some important condensation polymers are nylon, Bakelite, and formaldehyde polymer. Copolymerisation is a polymerisation reaction in which a mixture of more than one monomeric species is allowed to polymerise and form a copolymer. Rubber and its derivatives are copolymers.