Synthesis and characterization of methyl acrylate-copolymerized medium-chain-length poly-3-hydroxyalkanoates

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.