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

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 SN2 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 lead 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.