Creation of Environmental-benign polymer composites

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Biodegradable polymers do not possess the high mechanical properties, such as strength and elastic modulus, due to the aliphatic chain structure and its orientation and thereby they cannot replace high performance plastics. The composite of biodegradable plastics with reinforcement compensate this problem and hereby the reinforcement possessing not only the high mechanical properties but also good biodegradability is necessary. We have paid attention to prepare the whisker of polyglycolic acid (PGA). The polymers were synthesized in the heterogeneous (liquid-solid) solution polymerization in which an excess of solid glycolide coexists as a buffer to keep the very high glycolide concentration during polymerization in which temperature. As a result PGA whiskers were obtained as mixtures with dendrite crystals.The stereoselective synthesis of poly(l-lactic acid) (PLLA) is of great importance because the properties of PLLA are highly related to the stereoregularity. Here, the selective preparation of PLLA from partially rac-lactide is examined by the crystallization during ring-opening polymerization as a novel approach for stereoselective polymerization. Polymerizations of L-lactide and D,L-lactide were carried out at 80℃ in the mixed solvent of toluene and n-octane (40 / 60 by volume). The stereoselective polymerization occurs as follows. Once polymerization is started, homo-oligomer and co-oligomer formed are diastereomeric and thereby the physical properties become different. The homo-oligomers are preferentially precipitated to form the crystals at the early of polymerization due to the lower miscibility into solvent than that of co-oligomer. Thereafter, L-lactide is selectively polymerized at the active chain end of oligomers in the crystals with simultaneous crystallization. D,L-lactide is eliminated from the polymerization site on the crystals by segregation and the PLLA crystals containing less D-lactic acid unit are finally formed from partially rac-lactide