Mechanism of thermochemical degradation of bacterial poly-3-hydroxybutyrate in solutions.

Controlled thermal degradation of high-molecular-weight poly-3-hydroxybutyrate (PHB) was studied in dimethylformamide (DMF), bromoform, tetrabromoethane, and trichloropropane. Samples with molecular weights of 1.6 kDa and higher were obtained. PHB degradation in pure DMF and in trichloropropane resulted in the formation of C-terminal crotonic acid residues at the sites of polymer chain scission. In the case of bromoform and tetrabromoethane, 3-bromobutyric acid residues were formed (61–68% at 100 °C and 29–54% at 145 °C), along with crotonic acid residues. This indicates the possibility of halogen capture from solvent molecules at the moment of chain scission. Presumably, the reaction follows the E1 mechanism involving the formation of an intermediate carbocation. The results show the possibility of using thermochemical degradation of biodegradable polyesters in solutions for obtaining their oligomeric bromo-substituted derivatives. [ABSTRACT FROM AUTHOR]