CHEMICAL SYNTHESIS OF NOVEL BIODEGRADABLE POLYESTERS

Distannoxane complexes catalyze the ring-opening polymerization of optically active beta-butyrolactone (beta-BL) to afford a high molecular weight poly(3-hydroxybutyrate). When 1-ethoxy-3-chlorotetrabutyldistannoxane was used as a catalyst (catalyst/(R)-beta-BL = 1/8000 at 100 degrees C for 4 h), poly((R)-3-hydroxybutyrate) was obtained from (R)-beta-BL in a yield of 99%. The copolymerizations of (R)-beta-BL with racemic beta-BL in several ratios gave corresponding stereocopolymers. The copolymerizations of (R)-beta-BL with epsilon-caprolactone, delta-valerolactone, beta-methyl-delta-valerolactone, and L-lactide afforded novel optically active and biodegradable polyesters of high molecular weights, comprising (R)-3-hydroxybutyrate (3HB). The polymerization of (R)-beta-BL catalyzed by the distannoxane complexes proceeded by bond breaking between the carbonyl carbon and oxygen atom of the lactone ring (acyl cleavage) with retention of the configuration and little or no racemization. Polymers that have over 80 mol% of the (R)-3HB unit were found to have almost the same degree of biodegradability as the copolyester of 3-hydroxybutyrate and 11% 3-hydroxyvalerate produced by the microbial method.