One-Step Synthesis of Sequence-Controlled Polyester-block-Poly(ester-alt-thioester) by Chemoselective Multicomponent Polymerization

One-step chemoselective copolymerization of heterocyclic mixtures has been proved to be an efficient and straightforward approach to sequence-controlled (multi)block copolyesters compared with sequential addition and the macroinitiator method. However, the scope of the monomer substrates is limited to the oxygenated heterocycles, and cyclic monomers containing other heteroatoms are underexplored. In this work, we extended the chemoselective polymerization to sulfur-containing heterocycles and successfully synthesized sequence-controlled block copolymers polyester-block-poly(ester-alt-thioester)s from anhydride/thioanhydride/epoxide monomers. This is realized via highly selective copolymerization of anhydride/epoxide prior to thioanhydride/epoxide copolymerization using rationally designed aluminum-based catalysts bearing bipyridine bisphenolate ligands. A significant difference between the reactivity of anhydride and thioanhydride with alkoxide chain end led to the excellent chemoselectivity. Moreover, transesterification side reactions are completely inhibited even at a high temperature up to 80 degrees C during the copolymerization, resulting in block copolymers with well-defined sequence structure on the polymer chains. Chemoselective copolymerization is also highly controlled in the use of a family of different epoxide derivatives, providing a powerful tool box for creating various advanced polythioesters for many different applications.