Preparation of Truly Random Copolymers of Homogenous Composition by Equilibrium Ring-opening Copolymerization

无规共聚通常用于改善或修饰均聚物的性能。在无规共聚制备工业材料时，保持共聚物的组成恒定是非常重要的，因为组成的变化往往会降低材料的光学、热学和机械性能。但开环共聚很难制备出组成均匀的无规共聚物。在开环共聚中提出了“平衡开环共聚（ERC）”的新概念，即与不可聚合的共聚单体γ-丁内酯（BL）共聚可以得到真正统计的共聚物，并从理论上证明了这一概念的正确性。在ε-己内酯（CL）与BL的阴离子共聚反应中证实了这一概念的有效性，得到了组成均匀的共聚物，其中BL单元的含量<8 mol%。与常规共聚物不同的是，在整个共聚过程中，共聚物的组成几乎没有变化，但剩余单体的比例会随着共聚的进展而急剧变化。该共聚技术可以成功地应用于乙醇酸(GL)/BL和CL/THF体系的共聚，后者以阳离子引发剂三氟甲磺酸甲酯为研究对象，随着共聚单体初始浓度的增加，前者共聚单体的含量可达3%，后者共聚单体的含量可达50%。进一步研究了均匀性对聚CL-co-BL热降解性能的影响。通过在共聚体系中依次加入BL，制备了锥形组成的共聚物，以供参考。均相共聚物的T_m一般低于具有相似BL含量的非均相共聚物，而T_g不受均相性的影响。另一方面，非均相共聚物的结晶度略高于均相共聚物。均相共聚物比相应的非均相共聚物更易被生物降解。少

Random copolymerization is often carried out to improve or modify properties of homopolymers. In random copolymerization to prepare a commercial material, it is very important to keep the copolymer's composition constant as the variation in the composition often degrades the optical, thermal, and mechanical properties of material. However, it is difficult to prepare random copolymer of homogeneous composition by ring-opening copolymerization.A new concept in ring-opening copolymerization that a truly statistic copolyester is readily obtained by the copolymerization with a non-polymerizable comonomer, e.g.γ-butyrolactone (BL), was postulated under the name of "equilibrated ring-opening copolymerization (ERC)", and its appropriateness was proven theoretically. The validity of the concept was demonstrated for the anionic copolymerization between ε-caprolactone (CL) and BL, which gave copolymers of uniform composition containing <8 mol% of the BL units. Contrary to the conventional copolym … More erization, the copolymer's composition was hardly changed throughout the copolymerization, although the ratio between the remaining monomers was drastically changed according to the progress of copolymerization. This copolymerization technique could be successfully applied to the copolymerization between glycolide (GL)/BL and CL/THF systems, the latter was examined with methyl trifluoromethanesulfonate, a cationic initiator : the comonomer's content reached to 3% in the former case and 50% in the latter combination with increasing the comonomer's initial concentration.The effect of homogeneity on the thermal and biodegradable natures of poly(CL-co-BL) was further investigated. Copolymers of tapered composition were prepared by the sequential addition of BL into the copolymerization systems for reference. Homogeneous copolymer generally shows lower T_m than the heterogeneous copolymer having analogous BL content, while T_g was not influenced by the homogeneity. On the other hand, the crystallinity of heterogeneous copolymer was slightly higher than that of homogeneous copolymer. The homogeneous copolymer was biodegraded more readily than the corresponding heterogeneous copolymer. Less