Polymers for biodegradable medical devices. III. Polymerization and copolymerization of cyclic derivatives of...

The syntheses of anhydrosulphite and anhydrocarboxylate derivatives of tartronic acid are described. These compounds, more correctly named 5-carboxy-1,3,2-dioxathiolan-4-one-2-oxide and 5-carboxy-1,3-dioxolan-2,4-dione have been shown to undergo polymerization and copolymerization to poly-alpha-esters containing the tartonic acid residue, characterized by the presence of a pendant carboxyl group. Thermal polymerization of the anhydrosulphite appears to proceed in a substantially identical manner to other members of the series in which the monomer decomposes by a first order process to yield an alpha-lactone which polymerizes by a rapid chain growth reaction. Because the rate of thermal polymerization of tartronic acid anhydrosulphite is much more rapid than simple alkyl substituted anhydrosulphites, copolymerization favours the former residues. More successful copolymerization was achieved by the use of tertiary base initiators and the anhydrocarboxylate derivative of tartronic acid. The polymers and copolymers described are of potential value in the synthesis of drug-carrying biodegradable matrices or more hydrophilic analogues of poly(glycolic acid) which combine the known bioerodibility of the moiety with that presence of a pendant carboxyl group.