Library of Stereoregular Polythioesters for Stereocomplex Formation Enabled by Isomerization-Driven Cationic Ring-Opening Polymerization

Abstract

Supramolecular stereocomplexation is an important tool to advance sustainable polymers, and oxygen-containing polymers represent the most widely studied materials for stereocomplexation. However, the sulfur-containing analogues, a newly emerged class of sustainable polymers, remain essentially unexplored because of a significant challenge encountered in the synthesis of stereoregular polymers and relatively low supramolecular interaction. In this contribution, by the utilization of [Et₃O]⁺[B(C₆F₅)₄]⁻ as a metal-free cationic initiator, controlled isomerization-driven ring-opening polymerizations (IROPs) of nine examples of chiral five-membered thionolactones have been achieved with free or suppressed racemization via unique monomer-stabilized S_N2 propagation mechanism, which allows an unprecedented access to a library of new stereoregular polythioesters with high isotacticities (80.0%–99.5%). The investigations into structure–stereocomplexation relationship led to the disclosure of two new polythioester stereocomplexes with high melting temperatures (117.0–161.0 °C). The fundamental aspects of stereocomplex formation mechanism and critical factors that affect stereocomplexed ability have also been revealed.