AbstractDialkyl fumarates with bulky ester substituents were found to homopolymerize easily in the presence of 2,2′‐azobisisobutyronitrile. Among these fumarates, diisopropyl fumarate (DiPF) homopolymerized with the above initiator (20mmol/1) in bulk at 40∼60°C to give homopolymers with number‐average molecular weight of 70 000∼221 000. Similar results were also observed for di‐t‐butyl fumarate (DtBF) and Methyl‐t‐butyl fumarate (MtBF). These polymers were found to consist of a lessflexible rod‐like (polyalkoxycarbonylmethylene) from the molecular model and the solution property measurements. These polymers which were colorless powders did not melt before thermal degradation, but they were soluble in most organic solvents. From TG thermogram observed in a nitrogen atmosphere, the DiPF polymer showed T(init.)=257°C and T(max.)=316°C, and the main degradation products at 400°C, except gaseous materials, were isopropanol and DiPF monomer (32:1 in mole ratio). These thermal degradation behavior was different from that for the polymers of DtBF and MtBF which underwent degradation from lower temperatures like 190°C. Acid and alkaline hydrolyses of the DiPF polymer were obser