Dual Organocatalysts for Highly Active and Selective Synthesis of Linear Poly(γ-butyrolactone)s with High Molecular Weights

Ring-opening polymerization (ROP) of the bioderived and nonstrained γ-butyrolactone (γ-BL) is an emerging approach to produce recyclable polymers. It remains a big challenge to synthesize high molecular weight linear poly­(γ-butyrolactone)­s (PγBLs) in a highly active and selective manner. In this report, we developed dual organocatalysts for the ROP of γ-BL, using symmetrical (thio)­ureas with electron-donating groups to buffer the growing anions that were generared by the superbase phosphazene (P4). Linear PγBLs were selectively obtained with high apparent rate constant (ca. 39 times than single P4), and high number-average molecular weights of up to 64.3 kg/mol (ca. 3 times than single P4). The turnover frequencies of these P4/(thio)­urea pair-catalyzed processes were as high as 125 h–1. High molecular weight PγBLs exhibited dramatically improved mechanical properties