EN
Structural changes in polyhydroxybutyrate (PHB) brought about by addition of chain extender and/or plasticizer were studied using ^{13}C MAS NMR spectra, which were measured using the direct polarization technique at 30 and 98°C. Four resonances associated with the CO, CH, CH_{2} and CH_{3} groups of PHB were observed in the spectra. The CH_{3} resonance appearing at 98°C shows splitting into two lines related to the crystalline and amorphous regions. Analysis of the CH_{3} resonances made it possible to estimate the influence of applied modifications on crystallinity and distribution of conformations in amorphous and crystalline domains of PHB samples.