SYNTHESIS AND CHARACTERIZATION OF POLY(3-HYDROXYBUTYRATE) AND POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE) POLYMER MIXTURES PRODUCED IN HIGH-DENSITY FED-BATCH CULTURES OF RALSTONIA-EUTROPHA (ALCALIGENES-EUTROPHUS)

Alternate feeding of glucose and propionic acid to phosphate-depleted batch cultures of Ralstonia eutropha (reclassified from Alcaligenes eu trophus) produced poly(3-hydroxybutryate-co-3-hydroxyvalerate) [P(3HB- co-3HV)] with thermal properties markedly different from random copoly mers of similar monomer content. These polymers exhibited a single gla ss transition and a single melting peak that was significantly higher than expected for a random copolymer. The polymers were found, by solv ent fractionation and NMR, to be a mixture of poly(3-hydroxybutyrate) [P(3HB)] and a random copolymer, P(3HB-co-3HV). When compared with ran dom copolymers of similar monomer content, the polymers produced by al ternate substrate feeding displayed no improvement in mechanical prope rties and possessed similar aging characteristics.