Random copolymers from radical polymerisation

The value of the reachvity rahos is crihcal in determining the composition of the copolymer. If the reactivity raho is greater than 1, the radical prefers to react with chains having the same kind of terminal unit, e.g. A- with A. On the other hand, if the reactivity ratio is less than 1, the monomer prefers to react with chains which end in the other kind of monomer. In the special case that r r2 = 1, the reaction is described as ideal copolymerisation because it results in a truly random copolymer whose composition is the same as the composition of the reaction mixture from which polymerisation took place. 

The polymers were synthesised from boc-protected amine monomers and alkyl or benzyl methacrylate monomers. The polymerisation was performed by applying AIBN, as a radical initiator, and methyl 3-mercaptopropionate, as a chain transfer agent, in acetonitrile. The treatment of boc-protected polymers with TFA produced amphiphilic random copolymers with cationic ammoninm groups in the side chains. 

Polymers with more than one type of repeating unit are referred to as copolymers, and they are important in that they have properties different from either homopolymer. One example of a copolymer is polyethylene-vinylacetate which is widely used as a hot melt adhesive. Another is acrylic fibre where a small amount of comonomer added to acrylonitrile makes it easier to spin and to dye. In both these examples the monomers are mixed together and then polymerised by a free radical process the resulting copolymer has a random arrangement of the two units along the chain. Using more specific methods of polymerisation it is possible to prepare block and graft copolymers. 

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