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

The copolymerization of -[(benzyloxycarbonyl)methyl]-1,4-dioxane-2,5-d ione (BMD) and L-lactide (LAC) was carried out in bulk at relatively l ow BMD/LAC feed ratios with stannous 2-ethylhexanoate as the catalyst. The resulting copolymers were subjected to hydrogenolysis at atmosphe ric pressure in the presence of a palladium on charcoal catalyst to re move the pendant benzyl groups quantitatively. The deprotected copolym ers consisted Of L-lactic (L), glycolic (G) and L-alpha-malic acid (M) repeating units, with the copolymer composition being almost identica l to the monomer feed composition. C-13 n.m.r. spectroscopy revealed t hat the BMD units (G-M) had been randomly incorporated into the copoly mer (L-L). These poly(alpha-hydroxy acid)s with pendant carboxyl group s were found to hydrolyse more rapidly than poly(L-lactide), because o f the water-absorbing and catalytic activities of the carboxyl moietie s. They were allowed to react with p-azidophenacyl bromide in the pres ence of triethylamine to form photo affinity labelling groups at the c arboxyl 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.