A novel acid promoted ring‐opening polymerization of a seven‐membered cyclic carbonate initiated with BCl3

Ring‐opening polymerization of a seven‐membered cyclic carbonate, 1,3‐dioxepan‐2‐one, was investigated with a novel initiator system, BCl₃‐HCl·Et₂O. Addition of HCl·Et₂O promoted the polymerization even at 0°C to produce the corresponding polycarbonate with controlled molecular weight and narrow polydispersity ratio (< 1.2).