Perfectly Alternating and Regioselective Copolymerization of Carbonyl Sulfide and Epoxides by Metal‐Free Lewis Pairs

The preparation of perfectly alternating and regioslective copolymers derived from the copolymerization of carbonyl sulfide (COS) and epoxides by metal‐free Lewis pair catalysts composed of a Lewis base (amidine, guanidine, or quaternary onium salts) and a Lewis acid (triethyl borane) is described. Colorless and highly transparent copolymers of poly(monothiocarbonate) were successfully obtained with over 99 % tail‐to‐head content and high molecular weight (up to 92.5 kg mol−1). In most instances, oxygen–sulfur exchange reactions (O/S ERs), which would generate random thiocarbonate and carbonate units, were effectively suppressed. The turnover frequencies (TOF) of these Lewis pair catalyzed processes were as high as 119 h−1 at ambient temperature.