Radiation-induced graft polymerization of styrene onto poly(3-hydroxybutyrate) and its copolymer with 3-hydroxyvalerate

Graft copolymerization of styrene (St) onto poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-HV)) was carried out using simultaneous irradiation and pre-irradiation techniques with Co-60 gamma-rays. The degree of grafting (X-g) of styrene onto PHB increased with increasing pre-irradiation dose and grafting temperature while in the graft reaction of the copolymer, X-g was higher at 50 degrees C than at 70 degrees C. This X-g was lower than that in grafting methyl methacrylate (MMA) onto PHB and its copolymer. In the electron spin resonance (ESR) study, the PHB radical formed by irradiation was converted to a propagating radical by introducing St monomer at room temperature (25 degrees C) for grafting. The propagating radical was observed even at 50 degrees C and 70 degrees C, grafting of St onto PHB occurs actively at such temperatures. The decay of the radical concentration during grafting well corresponded to radical consumption in graft polymerization. The molecular weight ((M) over bar(n)) depended on the grafting conditions and the increase of the grafting temperature induced the formation of reduced (M) over bar(n) because of early termination. It was confirmed that the increase of X-g in pre-irradiation of more than 10 kGy was due to the increment of the graft chain.