New functional aliphatic polyesters were prepared by chemical modification of brominated copolyesters. Poly(epsilon -caprolactone)-co-poly(gamma-(2-bromo-2-methylpropionate)-epsilon -caprolactone) copolymer was prepared and successfully converted into copolyester bearing methacrylate double bonds by dehydrohalogenation of the pendant tertiary alkyl bromides, thus leading to cross-linkable polyester. The tertiary alkyl bromide groups of the original copolyester were also quaternized by reaction with pyridine, although some side reactions occurred which Limited the reaction yield. Nevertheless, quaternization of the bromide groups of the poly(epsilon -caprolactone)-co-poly(gamma -bromo-epsilon -caprolactone) copolymer proved to be quantitative and to occur without degradation of the polyester chains. This general strategy paves the way to either amphiphilic copolyesters or water-soluble polyesters. The poly(epsilon -caprolactone)-co-poly(gamma -bromo-epsilon -caprolactone) lactone) copolymer was also quantitatively converted into unsaturated copolyester by dehydrohalogenation with formation of double bonds including acrylic-type double bonds. As an alternative, gamma -bromo-epsilon -caprolactone was first dehydrohalogenated, and the unsaturated cyclic monomer was copolymerized with epsilon -caprolactone. Finally, the nonconjugated double bonds of the copolyesters were oxidized into epoxides, except for the acrylic-type unsaturations which remained unchanged.