Creation of Environmental-benign polymer composites

由于脂肪族链结构及其取向，生物可降解聚合物不具有高机械性能，例如强度和弹性模量，因此它们不能取代高性能塑料。生物降解塑料与增强体的复合材料弥补了这一问题，因此，增强体不仅具有高的机械性能，而且具有良好的生物降解性是必要的。本文着重研究了聚乙醇酸（PGA）晶须的制备。该聚合物是在多相（液-固）溶液聚合中合成的，其中过量的固体乙交酯作为缓冲剂共存以在聚合过程中保持非常高的乙交酯浓度。聚L-乳酸（PLLA）的立构规整性与其性能密切相关，因此，聚L-乳酸（PLLA）的立体选择性合成具有重要意义。在这里，选择性制备PLLA从部分外消旋丙交酯的开环聚合过程中的结晶作为一种新的立体选择性聚合的方法进行检查。以甲苯和正辛烷（体积比40 / 60）为混合溶剂，在80℃下进行L-丙交酯和D，L-丙交酯的聚合。立体选择性聚合如下进行。一旦聚合开始，所形成的均低聚物和共聚低聚物是非对映异构体，从而物理性质变得不同。由于均聚物在溶剂中的溶解性比共聚低聚物低，因此在聚合早期优先沉淀形成晶体。此后，L-丙交酯在晶体中的低聚物的活性链末端选择性聚合，同时结晶。D，L-丙交酯通过分离从晶体上的聚合位点消除，最终由部分外消旋丙交酯形成含有较少D-乳酸单元的PLLA晶体

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