Switchable Copolymerization of Maleic Anhydride/Epoxides/Lactide Mixtures: A Straightforward Approach to Block Copolymers with Unsaturated Polyester Sequences

Abstract

Switchable copolymerization of oxygenated heterocycle mixtures by a single catalytic system has been proved to be a promising approach to sequence-controlled block copolymers. However, there are still big challenges in one-step synthesis of multiblock copolymers containing unsaturated polyester blocks from maleic anhydride, epoxides, and lactone mixtures. Herein, a switchable pathway for polylactide-b-poly(MAH-alt-epoxide)-bpolylactide block copolymers is established. The excellent chemoselectivity in multicomponent copolymerization is achieved by bipyridine bisphenolate aluminum complexes that can induce an obvious kinetic differentiation between ring-opening copolymerization of maleic anhydride/epoxides and ring-opening polymerization of lactide. The scope of the epoxide for switchable copolymerization is explored and it is found that the steric hindrance of the substituents on epoxide significantly influences the formation of block copolymers. Block copolymers with various sequential and topological structures can be easily prepared by exquisite selection of different initiators. Furthermore, it is demonstrated that the conversion of cis-maleate units in the block copolyester could be completely converted to trans-fumarate units by isomerization without chain degradation, cross-linking, and chain scrambling.

Simple magnesium alkoxides: synthesis, molecular structure, and catalytic behaviour in the ring-opening polymerization of lactide and macrolactones and in the copolymerization of maleic anhydride and propylene oxide

“…68,69 Recently, block polyesters were obtained by chemoselective copolymerization from a multicomponent system formed by MA, PO, and LA with bipyridine bisphenolate aluminum. 70…”

“…8) of the resulting polymers showed signals attributable to both blocks and were fully consistent with those previously reported. 70…”

(Bipyridine bisphenolate)-aluminum/onium salt pair: a highly active binary catalyst for ring-opening polymerization of lactide with improved thermostability and protic tolerance

“…Recently, we synthesized a series of bipyridine bisphenolate aluminum (BpyBph-Al) complexes and used these complexes to catalyze maleic anhydride/epoxide copolymerization for the synthesis of unsaturated polyesters. 75–77 Compared with a typical (salen)Al/onium salt and Lewis pairs, the (BpyBph)Al/onium salt exhibited significantly improved tolerance to protonic impurities. Thus, the catalytic activity of the (BpyBph)Al/onium salt can be maintained at a low catalyst loading and high concentration of the chain transfer agent (100 equiv.…”