| Summary: | Synthesis of P(3HB-<i>co</i>-3HV-<i>co</i>-4HV) copolymers by the wild-type strain <i>Cupriavidus necator</i> B-10646 on fructose or sodium butyrate as the main C-substrate with the addition of γ-valerolactone as a precursor of 3HV and 4HV monomers was studied. Bacterial cells were cultivated in the modes that enabled production of a series of copolymers with molar fractions of 3HV (from 7.3 to 23.4 mol.%) and 4HV (from 1.9 to 4.7 mol.%) with bacterial biomass concentration (8.2 ± 0.2 g/L) and PHA content (80 ± 2%). Using HPLC, DTA, DSC, X-Ray, SEM, and AFM, the physicochemical properties of copolymers and films prepared from them have been investigated as dependent on proportions of monomers. Copolymers are characterized by a reduced degree of crystallinity (C<sub>x</sub> 38–49%) molecular weight characteristics M<sub>n</sub> (45–87 kDa), and M<sub>w</sub> (201–248 kDa) compared with P(3HB). The properties of the films surface of various composition including the porosity and surface roughness were studied. Most of the samples showed a decrease in the average pore area and an increase in their number with a total increase in 3HV and 4HV monomers. The results allow scaling up the productive synthesis of P(3HB-<i>co</i>-3HV-<i>co</i>-4HV) copolymers using <i>Cupriavidus necator</i> B-10646.
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