Alternating copolymerization of γ-selenobutyrolactone with episulfides for high refractive index selenium-containing polythioesters

Abstract

Polythioesters represent a promising functional polymer owing to the ubiquity and uniqueness of thioester bonds, however, to develop new examples of (functionalized) polythioesters for broadening the range of their applications is a grand challenge. Here, we report a convenient synthesis of a polythioester incorporating both thioester and selenide groups in repeating units via the alternating copolymerization of γ-selenobutyrolactone with episulfides including propylene sulfide and cyclohexene sulfide. This process mediated by a relatively mild phosphazene base of P1 exhibits very high activity with turnover of frequency (TOF) values of up to 1200 h−1, in which the nucleophilic attack of a selenol-type anion to episulfides is convinced as the rate-determining step by kinetic investigations. The prepared poly(thioester-alt-selenide)s have rigorously alternating sequences under optimized reaction conditions, molecular weights of 2.5–12.8 kg/mol, glass-transition temperatures of as low as −45.2 °C. Of unique, this copolymer exhibits remarkably high refractive indices of up to 1.74, suggesting a potential application prospect in optical materials.