Ring-opening copolymerizations of propylene oxide (PO) with cyclic acid anhydrides, succinic anhydride (SA), maleic anhydride (MA) and phthalic anhydride (PA) were carried out in the presence of a double metal cyanide (DMC) catalyst of molecular formula Zn(2.3)Cl(1.0)[Co(CN)(6)](1.0)center dot 2.0'BuOH center dot 1.0H(2)O as a means of developing functional polyols bearing ester backbones. Uniform alternating copolymers are produced when [PO]/[anhydride] in the copolymer approaches unity. All resulting copolymers have moderate molecular weights (M(n) = 2300-10,600) and a narrow polydispersity index (1.02-1.49). The apparent reactivity ratio of PO is 0.34, 0.28, and 0.26 for PO/SA. PO/MA, and PO/PA copolymerizations, respectively, assuming that the reactivity ratio of the anhydrides is zero. The DMC-catalyzed PO copolymerizations with anhydrides are an efficient way to produce polyester polyols, expanding the versatility of conventional polyols. (c) 2010 Elsevier Ltd. All rights reserved.