A series of functionalized poly(epsilon-caprolactone) copolymers, poly(epsilon-caprolactone-co-vinylphosphonic acid) and poly(epsilon-caprolactone-co-dimethyl vinylphosphonate), were synthesized by the free-radical copolymerization of 2-methylene-1,3-dioxepane with two vinyl monomers, vinylphosphonic acid and dimethyl vinylphosphonate. The copolymers have ester groups in the backbone as well as pendant functional groups. The structure of each copolymer was established by H-1 and C-13 NMR as well as IR spectroscopy. Differential scanning calorimetry indicated that the copolymer had a random structure. NMR study showed hydrogen transfer during the copolymerization. The copolymers have different solubility behavior due to the presence of different pendant functional groups.