A poly-??-hydroxy alkanoate (PHA) copolymer having a mean molecular weight of at least 10,000 and comprising monomers of the formulae: ##STR16## wherein n is an integer selected from the group consisting of 2, 4, 6, 8 and 10 and m is an integer selected from the group consisting of 0, 2, 4, 6 and 8.