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Radical copolymerization of medium-chain-length poly-3-hydroxyalkanoate (PHA) with methyl acrylate (MA) assisted by high-energy sound wave was investigated. Successful graft copolymerization of poly-3-hydroxyalkanoate –graft– poly-methyl acrylate (PHA-g-PMA) was inferred from the increase in molecular weight of initial neat PHA. The presence of PMA backbone in the graft copolymer was also authenticated by two additional proton peaks at 1.85 and 3.7 ppm. The concentration of PHA, MA and hydrogen peroxide (H2O2) showed significant effects towards the change in the graft copolymer molecular weight. The ideal amount of PHA, MA and H2O2 for graft copolymerization under ultrasonication were determined at 20 g L−1, 0.12 M and 20 μL, respectively. The copolymerizing process between PHA chains and PMA was investigated by analyzing the physicochemical properties of the produced graft copolymers. To this end, dielectric spectroscopy (DS) was used in corroboration to conventional thermal analyses, i.e., differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In addition, small-wide angle X-ray spectroscopy (SWAXS), field emission scanning electron microscopy (FESEM) and contact angle (CA) analysis were used to characterize the film morphology of the graft copolymers. From the results, it is suggested that PHA chains are subjected to pre-fragmentation prior to random grafting with PMA chains. [ABSTRACT FROM AUTHOR]

Methyl acrylate (MA) and medium-chain-length poly-3-hydroxyalkanoates (mcl-PHA) underwent "grafting through" copolymerization in an inert atmosphere with benzoyl peroxide as sole radical initiator. The effects of different concentrations of MA on the yield and properties of the graft copolymers (PHA-g-MA) were investigated. Successful grafting of mcl-PHA and poly-methyl acrylate (PMA) was validated from the increase in molecular weight (Mw) of starting mcl-PHA and the presence of methyl acrylate backbone indicated by two additional peaks in proton nuclear magnetic resonance (1H-NMR) spectrum. The hydrophobic graft materials were more resistant to strong alkali condition than neat mcl-PHA in addition to strong acid resistivity. Copolymerization affects the amorphous character of mcl-PHA, as evidenced by a significant reduction in glass transition temperature (Tg). Nonetheless, the degradation temperature (Td) of mcl-PHA was increased about 20 °C higher after copolymerization which indicates excellent thermal stability of grafted mcl-PHA. The graft copolymers also displayed increased dielectric constant (ε′) value except for PHA-g-MA synthesized from the highest concentration of MA (0.12 M) whereby it showed similar glass-to-rubbery transition and dielectric behavior to the neat mcl-PHA. Based on the results, the mechanism of the copolymerization is proposed. [ABSTRACT FROM AUTHOR]