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Graft copolymerization of styrene (St) onto poly(3-hydroxybutyrate) (PHB) andpoly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-HV)) was carried out using simultaneous irradiation and pre-irradiation techniques with 6oCo y-rays. The degree of grafting (X,) of styrene onto PHB increased with increasing pre-irradiation dose and grafting temperature while in the graft reaction of the copolymer, X, was higher at 50°C than at 70°C. This X, 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 "C) for grafting. The propagating radical was observed even at 50°C and 70"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 (Mn) depended on the grafting conditions and the increase of the grafting temperature induced the formation of reduced M, because of early termination. It was confirmed that the increase of X, in pre-irradiation of more than 10 kGy was due to the increment of the graft chain. ZUS AMMENFASSUNG: Die Pfropfcopolymerisation von Styrol (St) auf Poly(3-hydroxybutyrat) (PHB) und auf dessen Copolymeres Poly(3-hydroxybutyrat-co-3-hydroxyvalerat) (P(HB-HV)) wurde unter gleichzeitiger Anwendung von Bestrahlungs-und Vorbestrahlungstechniken mit 60Co-y-Strahlung durchgefuhrt. Der Pfropfungsgrad (X,) von Styrol auf PHB erhohte sich mit zunehmender Vorbestrahlungsdosis und Pfropfungstemperatur. Dagegen lag der Pfropfungsgrad des Copolymeren bei 50 "C hoher als bei 70°C. Verglichen mit der Pfropfung von Methylmethacrylat auf PHB und dessen Copolymeres wurden mit Styrol geringere Pfropfungsgrade erzielt. ESR-Untersu-

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