Fast, selective and metal-free ring-opening polymerization to synthesize polycarbonate/polyester copolymers with high incorporation of ethylene carbonate using an organocatalytic phosphazene base

摘要: Ring-opening polymerization (ROP) is a powerful method used for converting cyclic monomers to polymers, but ethylene carbonate (EC), which has five-membered ring, an exception owing the unfavorable thermodynamics of its ring-opening reaction unless release CO2. This behavior stems from faster cyclization form stable ring in comparison direct reaction. Hence, many attempts have been made copolymerize EC with other such as esters overcome thermodynamic barrier. In this context, copolymerization various esters, including e-caprolactone (CL), δ-valerolactone (VL) and L-lactide (LLA), successfully achieved using organocatalytic phosphazene superbase, trimeric base (CTPB). The random copolymerizations proceeded fast turnover frequency (TOF) 19 800 h−1 under mild conditions afforded corresponding copolymers without formation ether unit. Under all kinds experimental conditions, no homopolymerization occurred. molecular structures obtained P(EC-co-CL) were characterized 1H NMR 13C NMR, demonstrated that ca. 38 mol% can be incorporated within copolymer chain depending on different ratios CL monomers. With same catalytic system similar amounts into EC/VL (up 26 mol%) EC/LLA (ca. 4.8 lower than EC/CL copolymerization. 2D (1H–1H correlated spectroscopy (COSY), 1H–13C heteronuclear single quantum coherence (HSQC) multiple bond correlation (HMBC)) performed confirm assignments spectra better understand copolymers. Therefore, polycarbonate/polyester greater incorporation realized fast, selective metal-free process.