COPOLYMERIZATION OF 3-(S)-[(BENZYLOXYCARBONYL)METHYL]-1,4-DIOXANE-2,5-DIONE AND L-LACTIDE - A FACILE SYNTHETIC METHOD FOR FUNCTIONALIZED BIOABSORBABLE POLYMER

The copolymerization of 3-(S)-[(benzyloxycarbonyl)methyl]-1,4-dioxane-2,5-dione (BMD) and L-lactide (LAC) was carried out in bulk at relatively low BMD/LAC feed ratios with stannous 2-ethylhexanoate as the catalyst. The resulting copolymers were subjected to hydrogenolysis at atmospheric pressure in the presence of a palladium on charcoal catalyst to remove the pendant benzyl groups quantitatively. The deprotected copolymers consisted Of L-lactic (L), glycolic (G) and L-alpha-malic acid (M) repeating units, with the copolymer composition being almost identical to the monomer feed composition. C-13 n.m.r. spectroscopy revealed that the BMD units (G-M) had been randomly incorporated into the copolymer (L-L). These poly(alpha-hydroxy acid)s with pendant carboxyl groups were found to hydrolyse more rapidly than poly(L-lactide), because of the water-absorbing and catalytic activities of the carboxyl moieties. They were allowed to react with p-azidophenacyl bromide in the presence of triethylamine to form photo affinity labelling groups at the carboxyl functionalities. These findings suggested that the malic-acid-containing poly(alpha-hydroxy acid)s should have a high potential for use as functionalized bioresorbable polymers.