Chemical Synthesis of Crystalline Comb Polymers from Olefinic Medium-Chain-Length Poly[3-hydroxyalkanoates]

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. 13 C 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.