the present disclosure relates to a new polymerisation process in which ethylenically unsaturated monomers are polymerised by a living radical polymerisation process in the presence of an initiator and a catalyst . polymers produced by this new process are also thought to be novel and may be used to derivatise biological molecules to improve their efficacy as therapeutic treatments . a preferred polymer is of formula the polymers are particularly suitable for derivatising proteins , such as interferon - α .