Ring-Opening Co- and Terpolymerization of Epoxides, Cyclic Anhydrides, and L-Lactide Using Constrained Aluminum Inden Complexes

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 Tg ranging from 49 to 226 degrees 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.