Production and characterization of poly(3-hydroxybutyrateco-3-hydroxyhexanoate)-poly(ethylene glycol) hybird copolymer with adjustable molecular weight

 A novel natural-synthetic hybrid block copolymer was synthesized by Aeromonas hydrophila 4AK4 in poly(ethylene glycol) (PEG, M_n = 200) modified fermentation. This hybrid biomaterial consists of the natural hydrophobic polymer poly(3-hydroxybutyrat-co-3-hydroxyhexanoate) (PHBHHx) end-capped with hydrophilic PEG, which has the increased flexibility as well as the improved thermal stability. Addition of diethylene glycol (DEG) and ethylene glycol could not result in the accumulation of hybrid block copolymer. DEG and ethylene glycol, together with PEG-200, could cause a reduction of molar mass of PHBHHx, resulting in a series of low molecular weight polymer and the reduction of the polymer yield as well as the cellular productivity. In vitro degradation of PHBHHx and PHBHHx-PEG with different molecular weight showed that the decrease of molecular weight accelerated the degradation of copolymers, but PEG modification has little effect on its degradation rate. The results in this study provided a convenient and direct method to produce a series of PHBHHx and PHBHHx-PEG materials with adjustable molecular weight and broad molecular weight distribution which will be very useful for the biomedical applications.