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

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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