RADIATION-INDUCED GRAFT-POLYMERIZATION OF POLY(3-HYDROXYBUTYRATE) AND ITS COPOLYMER

Graft copolymerization of methyl methacrylate (MMA) or 2-hydroxyethyl methacrylate (HEMA) onto poly(3-hydroxybutyrate) (PHB) and its copolymer poly( 3-hydroxybutyrate-co-3-hydroxyvalerate) {P(HB-HV)} was carried out by using simultaneous radiation and preirradiation techniques from a Co-60 gamma-rays source. Degree of grafting (X(g)) of MMA onto both polymers increased as the irradiation dose increased. The X(g) for PHB graft-polymerized by simultaneous radiation was lower than that for the copolymer of 24 mol% HV content (24 M sample). On the contrary, X(g) of PHB graft-polymerized after preirradiation was higher than that of the 24 M sample. The X(g) depended on differences in regularity in the crystalline regions or crystallinity and rate of radical decay. Crystalline regions of PHB remained almost unchanged after grafting, while crystalline regions of the 24 M sample were partially destroyed by the introduction of grafting. Glass transition temperatures of both grafted polymers increased up to 8 degrees C. The number-average molecular weight (($) over bar M(n)) of grafted PMMA was comparable to that of trunk polymers, while ($) over bar M(n) of that graft-polymerized with simultaneous radiation was far larger, reflecting the introduction of crosslinking. Biodegradability steeply decreased by the introduction of MMA grafting, while that grafted with HEMA increased at first because of improvement of wettabiity between the polymer and an enzyme solution, then steeply decreased as X(g) increased.