Rates of increase and decrease for each block of poly(3-hydroxybutyrate)(P3HB)-b-poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(P3HBV) and P3HBV-b-P3HB during biosynthesis by Ralstonia Eutropha

The number-average molecular weights (M_ns) of the first and second blocks of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HBV)-b-poly(3-hydroxybutyrate) (P3HB) and P3HB-b-P3HBV block copolymers biosynthesized from Ralstonia eutropha were investigated. Pentanoic acid and glucose were used as carbon sources for the biosynthesis of the blocks of P3HBV and P3HB, respectively. The cultivation time for the first carbon source was fixed at 72 h, and that for the second carbon source was varied. The first and second blocks for P3HBV-b-P3HB and P3HB-b-P3HBV showed a decrease and increase in the M_n, respectively; this indicates that degradation and polymerization proceeded at the initial end of the first block and at the other end of the second block, respectively. In the biosynthesis of P3HBV-b-P3HB, the rates of decrease and increase in the M_n for the P3HBV and P3HB blocks were 9.0 × 10³ and 2.9 × 10⁴ g/(mol∙h), respectively. For P3HB-b-P3HBV, the rates of decrease and increase in the M_n were 2.6 × 10³ and 2.0 × 10³ g/(mol∙h) for P3HB and P3HBV, respectively.