Synthesis and Characterization of Multicomponent PHAs

Abstract

Cupriavidus necator B10646 bacterial cells were cultivated in the mode of synthesis of the reserve polyhydroxyalkanoates (PHAs) in the growth medium that contained, in addition to glucose as the main substrate, precursor substrates of the monomers of various monocarboxylic acids – salts of valeric and hexanoic acids, propionate, and γ-butyrolactone. PHA terpolymers and quaterpolymers with different compositions and proportions of monomers were synthesized, and their physicochemical properties were studied. The terpolymers were composed of monomers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 4-hydroxybutyrate (4HB), or 3-hydroxyhexanoate (3HHx) and had the following compositions: P(3HB/3HB/4HHx) and P(3HB/3HV/4HHx). The quaterpolymers had the following composition: P(3HB/3HV/4HB/3HHx). All copolymer samples, regardless of the composition and proportions of monomers, had lower molecular weights and higher polydispersity values compared to the highly crystalline 3-hydroxybutyrate homopolymer, but retained thermal stability properties, with a difference between the melting point and thermal degradation of at least 100-110 °С. The inclusion of 3HV, 4HB, and 3HHx monomers in the C-chain of 3HB caused changes in the crystalline to amorphous phase ratio and a significant decrease in the degree of crystallinity (Cx), which depended on the type of monomers and their contents in the copolymer. The maximum decrease in Cx (9-17 %) was detected in the P(3HB/3HV/4HB) terpolymer and the P(3HB/3HV/4HB/3HHx) quaterpolymer (30-36 %). The study confirms that there is the possibility of synthesizing polymers with various compositions, including new ones, which differ significantly in their basic properties