A copolymer of formula 1 in which M1 is a unit obtainable from ring opening metathesis polymerization (ROMP); R is an alkyl, ether, ester or aryl unit; M2 and M3 are independently selected from units obtainable by reversible addition fragmentation chain transfer polymerization (RAFT); X is a terminal unit selected from the group consisting of dithioester, trithiocarbonate, xanthate; and m is an integer from 2 to 1 million, n is an integer from 2 to 500,000 and k is an integer from 2 to 500,000.