Graft Copolymerization of N-Vinylpyrrolidone onto Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate) in Homogeneous Solution

Poly(N-vinylpyrrolidone) (PVP) groups were grafted onto poly(3-hydroxybutyrateco-3-hydroxyvalerate) (PHBV) backbone in a homogeneous solution using benzoylperoxide (BPO) as an initiator and chlorobenzene as solvent. The structureof raw PHBV and grafted PHBV was characterized by FTIR and 1H NMR spectra. Theexistence of chemical bonds more likely the covalent bonds between PVP groups andPHBV substrate was verified by the comparative analysis of weight reduction and 1HNMR spectra change of PHBV/PVP blends and grafted PHBV after selective extraction.The effects of various reaction conditions such as monomer concentration, initiatorconcentration, reactiontemperature and reaction time on the percentage of conversion(PC%), graft yield (G%), and graft efficiency (GE%) were investigated. In orderto obtain the higherG% and GE%, the reaction should be carried out at the reactiontemperature above 100ºC for PHBV cannot dissolve completely in chlorobenzenebelow this temperature at the given concentration. Grafted PHBV with the highest G%of 10.48% was obtained at the optimal reaction conditions: the NVP concentration of0.4 g/mL, BPO concentration of 0.024 g/mL, the reaction temperature of 120ºC andthe reaction time of 1 h. The thermal properties of raw PHBV and grafted PHBV wereevaluated with a simultaneous thermal analysis system. The results showed that thethermal stability of grafted PHBV samples was remarkably improved, which wasdependent on G%. When the G% reached 10.48%, the decomposition temperature (Td) of grafted PHBV increased to nearly 30ºC compared to raw PHBV, while the melting temperature (Tm) of all samples was almost constant.