Since free radical ring-opening polymerization made it possible to introduce functional groups, such as esters, carbonates, thioesters, and amides, into the backbone of an addition polymer, it was reasoned that simple hydrolysis of these copolymers would produce the desired oligomers that could be terminated with various combinations of hydroxyl, amino, thiol, and carboxy1 groups. Thus the copolymerization of 2-methylene-1,3-dioxepane and styrene (r1=0.021 and r2=22.6) gave a copolymer containing 10 mole-percent of an ester-containing unit with 100% ring opening at 120°C. Hydrolysis of this copolymer gave an oligomer terminated with a hydroxyl group and a carboxylie acid group. Similarly the copolymerization of 2-methylene-1,3-dioxepane and ethylene gave a series of biodegradable polyethylene copolymers containing 2.1 to 10.4% ester-containing units. Hydrolysis of these copolymers gave a series of ethylene oligomers with nine to forty-seven ethylene units and terminated with a hydroxyl group and a carboxylic acid group. By the same general method oligomers of various monomers that are terminated with a methylandno group and a carboxylic acid group from N-methyl-Z-methylene-1,3-oxazolidine and with a thiol group and a carboxyl group from Z-methylene-1,3-oxathiolane.