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

为了改善或改善均聚物的性能，经常进行无规共聚合。在无规共聚制备商业材料时，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、热和机械性能。然而，开环共聚很难制备出组成均一的无规共聚物。在开环共聚中提出了一种新的概念，即通过与不可聚合的共聚单体(如γ-丁内酯(BL))进行共聚而得到真正统计的共聚酯，并从理论上证明了其合理性。对于ε-己内酯(CL)与BL的阴离子共聚反应，证明了该概念的正确性，得到的共聚物组成均匀，含有-lt；8mol%的BL单元。与传统的共聚…相反此外，在整个共聚过程中，共聚物的组成几乎没有变化，尽管剩余单体之间的比例随着共聚过程的进展而发生了很大的变化。该共聚技术可成功地应用于乙交酯(GL)/BL和CL/THF体系的共聚反应，以阳离子引发剂三氟甲磺酸甲酯为引发剂，随着共聚单体初始浓度的增加，前者的共聚单体含量可达3%，后者的共聚单体含量可达50%，并进一步研究了均匀度对聚(CL-co-BL)热性能和生物降解性的影响。通过在共聚体系中连续加入BL制备了锥形组成的共聚物，以供参考。均相共聚物的玻璃化转变温度普遍低于具有相似BL含量的非均相共聚物，而玻璃化温度不受均质度的影响。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容易生物降解。较少

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