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

Ring-opening polymerization (ROP) of the bioderived and nonstrained gamma-butyrolactone (gamma-BL) is an emerging approach to produce recyclable polymers. It remains a big challenge to synthesize high molecular weight linear poly(gamma-butyrolactone)s (P gamma BLs) in a highly active and selective manner. In this report, we developed dual organocatalysts for the ROP of gamma-BL, using symmetrical (thio)ureas with electron-donating groups to buffer the growing anions that were generared by the superbase phosphazene (P4). Linear P gamma BLs 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 P gamma BLs exhibited dramatically improved mechanical properties.