Two ways to obtain aliphatic polyesters (PEs) from dimethylketene and acetaldehyde were investigated. On the one hand, a direct anionic copolymerization was carried out in toluene at -60 degrees C. The resulting polymer was mainly composed of PE units. On the other hand, a two-step process involving the synthesis of 3,3,4-trimethyl-2-oxetanone by [2+2] cycloaddition, followed by its ring-opening polymerization, with various initiators and solvents, led to the expected PE. Molecular weights up to 9000 g mol(-1) (measured by nuclear magnetic resonance (NMR)), with narrow polydispersity around 1.2, were obtained. These polymers were found stable up to 274 degrees C under nitrogen and a broad and complex endothermic peak attributed to crystallinity was observed near 139 degrees C by differential scanning calorimetry (DSC). The crystallinity, measured by X-ray diffraction, was close to 0.45. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4129-4138, 2011