In this study, we attempted to graft vinyl acetate (VAc) onto a PHB film because the grafted poly(vinyl acetate) could be transformed into degrad- able poly(vinyl alcohol) (PVA) after saponification treatment. It is known that PVA can be degraded completely by a degradative enzyme.12,13 Thus, the purpose of grafting VAc onto the PHB film is to obtain a film with controllable biodegradability and the ability to degrade completely after saponification.
The PHB grafted with VAc films (PHB-g-VAc) was prepared by preirradiation techniques of radiation- induced graft polymerization. Xg was controlled by changes in the monomer concentration during a typ- ical grafting reaction. However, the polymerization reactivity of the VAc monomer was very low. Therefore, some VAc polymerization methods were stud- ied to improve the polymerization reactivity. As one of the improved processes, VAc emulsion polymerization has been extensively studied.14 The degree of polymerization of VAc was increased exponentially by the use of this emulsion polymerization method. In this study, we applied this emulsion polymerization method to the grafting reaction of VAc on the surface of PHB films. Initially, the best surfactant was selected on the basis of the stability of the VAc emulsion prepared. We then investigated the optimum VAc and surfactant concentrations during the grafting reaction. The grafting reactivity of the emul-

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sion system was compared with those of VAc/water, VAc monomer, and VAc/methanol systems.