The side-chain double bonds of bacterial poly [3 -hydroxyalkanoate-co-3-hydroxyalkenoate] (PHAE, 1) were transformed into thioether bonds (derivative 2) via the radical addition reaction of 11-mercapto-1-undecanol. The terminal hydroxy functionalities of derivative 2 were subsequently esterified with cinnamic acid (derivative 3), sulfatized with ClSO3H (derivative 4), or coupled with tert-butyldimethylsityl-protected coumaric acid, to give, after deprotection with tetrabutylammonium fluoride (derivative 5) followed by sulfatization, p-(sulfooxy) cinnamic acid- (zosteric acid) labeled PHAE (derivative 6). The reactions proceeded with good yields and little side reactions, which was confirmed with H-1 NMR and GPC experiments. These functionalized polyesters are currently investigated as environmentally friendly coatings to protect surfaces from biofouling.