Activated monomer cationic ring-opening polymerization of epsilon-caprolactone (epsilon-CL) and delta-valerolactone (delta-VL) and the synthesis of di- and triblock copolymers of a seven-membered cyclic carbonate (7CC) and these lactones initiated with n-butyl alcohol/HCl . Et2O and H2O/HCl . Et2O were carried out to obtain the corresponding homopolymers and block copolymers with narrow polydispersity ratios in one pot quantitatively. The molecular weights of the obtained polymers could be controlled with the feed ratio of the monomer and initiator.