Comb polymers were produced in a two-step synthesis from a bacterial poly [3-hydroxyalkanoate-co-3-hydroxyalkenoate] (PHOU, 1) containing 25 mol % terminal side-chain double bonds. The radical addition reaction of 11-mercaptoundecanoic acid to the side-chain alkenes of 1 produced derivative 2 containing thioether bonds with terminal carboxyl functionalities, which were subsequently transformed into the amide (3) or ester (4) derivatives using tridecylamine or octadecanol, respectively. The reactions proceeded to completion with little side reactions, which was confirmed with NMR and GPC experiments. The resulting comb polymers 3 and 4 were white crystalline materials. C-13 CP/MAS NMR spectra and X-ray diffraction results suggested a crystalline textural two-phase organization into polyethylene-like domains and regions characteristic of poly [3-hydroxyalkanoates] (PHAs). The breadth of the decomposition steps in thermal gravimetric analysis and the diffuse melting endotherms confirmed the solid-state organization as composed of nanosize crystallites of both polyethylene and PHAs.