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 benzoyl peroxide (BPO) as an initiator and chlorobenzene as solvent. The structure of raw PHBVand grafted PHBV was characterized by FTIR and 1H NMR spectra. The existence of chemical bonds more likely the covalent bonds between PVP groups and PHBV substrate was verified by the comparative analysis of weight reduction and 1H NMR spectra change of PHBV/PVP blends and grafted PHBV after selective extraction. The effects of various reaction conditions such as monomer concentration, initiator concentration, reaction temperature and reaction time on the percentage of conversion (PC%), graft yield (G%), and graft efficiency (GE%) were investigated. In order to obtain the higher G% and GE%, the reaction should be carried out at the reaction temperature above 100°C for PHBV cannot dissolve completely in chlorobenzene below 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 of 0.4 g/mL, BPO concentration of 0.024 g/mL, the reaction temperature of 120°C and the reaction time of 1 h. The thermal properties of raw PHBV and grafted PHBV were evaluated with a simultaneous thermal analysis system. The results showed that the thermal stability of grafted PHBV samples was remarkably improved, which was dependent on G%. When the G% reached 10.48%, the decomposition temperature (Td) of grafted PHBV increased to nearly 30°C compared to raw PHBV, while the melting temperature (Tm) of all samples was almost constant.