Thermal decomposihon processes in poly(β-hydroxybutyrate)(PHB) and Poly (β-hydroxybutyrate-co-β-hydroxyvalerates) [P(HB-co-HV)s] with composihon ratios HB/HV of 96:4 and 82:18 were investigated by direct pyrolysis mass spectrometry (DPMS). It can provide up to hoptelner pyrolynates and estimate the composition and sequence distribution of copolymers. The results indicate that the thermal degradation of PHB and P(HB-co-HV) occurs quite selctively through a β-Hydrogen transfer process

with formation of oligomers bearinng carboxyl and olefin end-groups. Oligomeri groducts corresponding to dehydrated monomer up to heptamer were also identified both in the case of PHB and P(HB-co-HV).