Isotactic-Rich Polythioethers Synthesized from Asymmetric Ring-Opening Polymerization of Racemic Terminal Thiiranes

The ring-opening polymerization (ROP) of thiiranes constitutes a straightforward route to fabricating diverse polythioethers. However, poor stereochemical control during polymerization results in a low tacticity of the obtained polythioethers, which exhibit weak thermal and mechanical properties. Herein, we propose to obtain isotactic-rich polythioethers directly from racemic thiiranes via the kinetic resolution ROP of thiiranes using a dinuclear Cr^III complex. The ROP of rac-(phenoxymethyl)thiirane (rac-POMT) proceeds via a kinetic resolution polymerization mechanism and affords poly((phenoxymethyl)thiirane) (PPOMT), with isotacticity reaching 92%. Notably, the highly isotactic PPOMT exhibited a crystalline nature with a melting temperature (T_m) of 121 °C, whereas the atactic PPOMT exhibited an amorphous nature with a glass transition temperature (T_g) of 22 °C. Consequently, the isotactic-rich PPOMTs exhibited enhanced mechanical performance, including strain, stress at break, and storage modulus, compared to that of the atactic PPOMTs. This strategy provides a category of poly(thioether)s with good properties and presents a methodology for acquiring isotactic-rich sulfur-containing polymers.