Radical ring-opening polymerization has been efficiently used to copolymerize 2-methylene-1,3,6-trioxocane (MTC) and 2-methylene-1,3-dioxepane (MDO). The cyclic ketene acetal MTC was first synthesized and homopolymerized at different temperatures using either 2,2-azobisisobutyronitrile or dicumyl peroxide as initiator. The polymerization mechanism was not temperature-dependent, and the polymerization proceeded with 100% ring-opening at all the temperatures evaluated. The structures of MTC and PMTC were verified by H-1-nuclear magnetic resonance (NMR) and C-13-NMR spectroscopies. A number-average molecular weight of 6500 was obtained after 2 days at 70 degrees C in bulk, which was somewhat higher than the theoretical molecular weight. A significant amount of branching was detected from the high polydispersity index as well as the glass-transition temperatures. The polyester-ether was then successfully obtained by copolymerization of MTC with MDO. Different feed ratios and temperatures were used to map the reaction, and the copolymers were characterized by NMR, size exclusion chromatography, and differential scanning calorimetry. The amount of MTC within the polymer was independent of the feed ratio and always higher than the amount of MDO. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4965-4973, 2010