RESUMO
A series of two-component polyhydroxyalkanoates consisting of hydroxybutyrate and hydroxyvalerate monomer at different ratios were synthesized using the bacterium Ralstonia eutropha B5786. The properties of polyhydroxyalkanoates were compared with those of the homopolymer of hydroxybutyric acid by X-ray structure analysis, IR spectroscopy, differential scanning calorimetry, and viscosimetry. With an increase in the molar fraction of hydroxyvalerate, an equalization of the ratio of the crystalline and amorphous phases in the copolymer was observed. The degree of crystallinity of the polymer decreased from 70-80 to 45-50%; in the range of an increase in the hydroxyvalerate molar fraction from several to 25-30 mol%, the dependence was linear. The temperature characteristics, the melting temperature (T(m)), and the degradation temperature (T(d)) were lower in polyhydroxyalkanoates than in polyhydroxybutyrate, for which T(m) and T(d) were 168-170 and 260-265 degrees C, respectively. In the copolymer, as the molar fraction of hydroxyvalerate grew, both parameters decreased. In the range of variation of monomer ratio studied, they decreased to 150-160 and 200-220 degrees C, respectively. No distinct correlation between the composition of the polymer and its molecular mass was found.
