Free-radical polymerization of tetraethyl (2,3-dimethylenebutane-1,4-diyl)bis(phosphonate), a 1,3-butadiene derivative containing two diethyl phosphonate functions in a molecule, was carried out under various conditions. When polymerization was performed in benzene at 60°C for 21 h with using 1 mol% of 2,2′-azobisisobutyronitrile as an initiator, sticky polymer was obtained in 70% yield without forming gel. Number average molecular weight of the polymer thus obtained was estimated to be 69,000 by SEC based on polystyrene calibration using N,N-dimethylformamide as an eluent. The rate of polymerization was found to be proportional to 0.5 and 1.5 power of the initiator and the monomer concentration, respectively. The overall activation energy of polymerization was determined to be 91.4 kJ/mol. The microstructure of the polymer was exclusively 1,4- but both E and Z configurations were contained. Glass transition temperature of the polymer was -18°C. Monomer reactivity ratio of the monomer with styrene as comonomer was determined to be r_st=0.15, r₂=6.1.