Copolyesters of ϵ‐Caprolactone, Isosorbide and Suberic Acid by Ring‐Opening Copolymerization

Biodegradable copolyesters were prepared by copolymerization of ϵ‐caprolactone (ϵCL) with a cyclic polyester consisting of isosorbide and suberic acid (CPIS). Four initiators were compared: Sn(II)2‐ethylhexanoate (SnOct2) in combination with benzyl alcohol, 2,2‐dimethyl‐2‐stanna‐1,3‐dioxepane (DSDOP) lanthanium and yttrium tris(isopropoxide). For SnOct2 (combined with benzyl alcohol) and DSDPO temperature and time were varied. The highest molecular weights were obtained at the highest temperature. However, the compositions of the copolyesters varied largely. Whereas SnOct2 favored the incorporation of CPIS, DSDOP favored incorporation of ϵCL. A similar difference was found for La(OiPr)3 favoring ϵCL and Y(OiPr) favoring incorporation of CPIS. 13C NMR spectroscopy proved that SnOct2 yielded blocky sequences and mixtures of homo‐polyesters. A greater extent of transesterification and a tendency towards random sequences was observed for DSDOP catalyzed copolymers. All reaction products contained crystallizing blocks of ϵCL units. The melting temperatures decreased with the extent of transesterification.