Abstract: A method of producing polyhydroxyalkanoate (PHA) copolymers comprising both short-chain-length (scl) and medium-chain-length (mcl) subunits, wherein some of the mcl subunits bear reactive vinyl groups, is provided. The method comprises providing cells comprising (i) a PHA synthase (phaC) gene encoding a particular class I poly(3-hydroxyalkanoate) polymerase, and (ii) a phaJ gene encoding a particular (R)-specific enoyl-CoA hydratase, and cultivating said cells in a growth medium comprising an alkenoic acid. In one example, cells grown in the presence of a mixture of decanoic acid and undecen-10-enoic acid yielded a copolymer comprising units of 3-hydroxybutyrate (94.73 mol %), 3-hydroxyhexanoate (1.51 mol %), 3-hydroxyoctanoate (2.33 mol %), 3-hydroxydecanoate (0.69 mol %) and 3-hydroxyhept-6-enoate (0.73 mol %). The presence of acrylic acid as a 13-oxidation inhibitor in the growth medium led to an increase in both the mcl-PHA subunit content and vinyl subunit content.