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

Graft copolymerization of methyl methacrylate (MMA) or 2-hydroxyethyl methacrylate (HEMA) onto poly(3-hydroxybutyrate) (PHB) and its copolym er poly( 3-hydroxybutyrate-co-3-hydroxyvalerate) {P(HB-HV)} was carrie d out by using simultaneous radiation and preirradiation techniques fr om a Co-60 gamma-rays source. Degree of grafting (X(g)) of MMA onto bo th polymers increased as the irradiation dose increased. The X(g) for PHB graft-polymerized by simultaneous radiation was lower than that fo r the copolymer of 24 mol% HV content (24 M sample). On the contrary, X(g) of PHB graft-polymerized after preirradiation was higher than tha t of the 24 M sample. The X(g) depended on differences in regularity i n the crystalline regions or crystallinity and rate of radical decay. Crystalline regions of PHB remained almost unchanged after grafting, w hile crystalline regions of the 24 M sample were partially destroyed b y the introduction of grafting. Glass transition temperatures of both grafted polymers increased up to 8 degrees C. The number-average molec ular 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 introductio n of crosslinking. Biodegradability steeply decreased by the introduct ion of MMA grafting, while that grafted with HEMA increased at first b ecause of improvement of wettabiity between the polymer and an enzyme solution, then steeply decreased as X(g) increased.