Typical ring-opening copolymerization (ROCOP) of cyclic anhydrides (A) and epoxides (B) catalyzed by most metal complexes underwent strict alternating monomer insertions giving (AB) n polyesters. In this contribution, a novel polyester containing (ABB) n polymer sequences was prepared via the ROCOP of cyclic anhydrides and cyclohexene oxide (CHO) using a tin­(II) alkoxide complex. Quantum calculations revealed that the preference for the (ABB) n sequence was enhanced by the energetic preference of the second CHO insertion. The copolymer with (ABB) n content as high as 70% was obtained from the ROCOP of succinic anhydride and CHO with an enhanced T g of 65 °C (>20 °C higher than the (AB) n analogue). The ROCOP of maleic anhydride and CHO also gave a copolymer with high (ABB) n content at 48% and improved T g of 89 °C (38 °C higher). The improved thermal properties were a result of the more rigid (ABB) n polymer backbone compared with conventional alternating (AB) n copolymer analogues. In addition, terpolymerization with ε-caprolactone (ε-CL) was achieved by sequential addition of ε-CL affording the block copolymer with the (ABB) n backbone.

Seven constrained aluminum inden complexes having different substituents and diamine backbones were developed for the ring-opening copolymerization (ROCOP) of epoxides and bulky cyclic anhydrides giving alternating polyesters with T g ranging from 49 to 226 °C. Among several catalyst/cocatalyst screenings, the aluminum inden complex having a rigid phenylene backbone coupled with 4-dimethylaminopyridine showed the best performance giving linear polyesters. In the case of cyclohexene oxide (CHO) and succinic anhydride (SA), the linear poly(CHO-alt-SA) could be transformed to cyclic polymer when the polymerization was left under prolonged reaction time to induce intramolecular transesterification. The kinetic studies of the ROCOP revealed a zeroth-order dependence on cyclic anhydride and a first-order dependence on epoxide and the catalyst. The catalysts can be extended efficiently to the one-pot CHO/PA/l-lactide terpolymerization giving uncommon tapered copolymers of poly(CHO-alt-PA) and PLA via switchable polymerization.

Bis(amidinate) tin(II) complex (1) was reported as active catalyst for ring‐opening copolymerization of cyclic anhydrides and epoxides via a binary catalyst system. Polymerizations of six combinations of epoxides and cyclic anhydrides were carried out giving highly alternating poly(anhydride‐alt‐epoxide) with narrow dispersities, except for cyclohexene oxide where significant amount of ether linkage up to 62 % was observed. This ether linkages could be diminished by increasing the amount of cocatalyst to over 3 equiv. Six well‐known cocatalysts were screened where PPNCl was found to be the best cocatalyst.