Fast and switchable ring-opening polymerization of biorenewable omega-substituted lactones towards sustainable copolymers with facile control over monomer sequences

Abstract

Highly active catalysts for the ring-opening polymerization (ROP) of biorenewable monomers, especially lactones, are essential for sustainable polymers. (Thio)urea/base catalyst systems have been found to be active for unsubstituted lactones. However, while omega-substituted lactones are an important class of biorenewable monomers, the ROP of such lactones suffers from low polymerization rates, and (thio)ureas usually show low catalytic activity for omega-substituted lactones due to their high steric hindrance. Herein, fast and controlled ROPs of omega-substituted lactones, including ε-decalactone (ε-DL), δ-caprolactone (δ-CL) and δ-decalactone (δ-DL), were achieved using cheap and commercially available (thio)urea/base catalyst systems, whose activities were significantly improved by pairing the pK_as of (thio)ureas with bases. (Thio)urea/IMes pairs exhibited superior activity, with the most active TU3/IMes showing turnover frequencies of 270 h⁻¹, 996 h⁻¹ and 331 h⁻¹ in the ROP of ε-DL, δ-CL and δ-DL, respectively. Moreover, the block, gradient and random copolymer chain sequences can be facilely modulated by different catalyst pairs during the copolymerization of ε-caprolactone (ε-CL) and ε-DL to match different application scenarios. Therefore, this work provides fresh ideas for the transformation of similar low-activity catalysts to high-activity ones and contributes to the efficient construction of structurally and functionally diverse biorenewable polymer materials.