Changes in diad sequence distribution by preferential chain scission during the thermal hydrolysis of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Specific hydrolysis properties of microbial copolyester P(3HB- co -6%-3HHx) was found during super-heated steam treatment in a temperature range of 130–190 °C. From changes in diad sequences on 13 C nuclear magnetic resonance spectra, preferential and suppressive chain scission of HHx*HB and HB*HHx sequences, respectively, were determined. These specific reaction properties were considered to be contributed by higher steric propyl group in HHx unit than methyl group in HB unit, that is, promoting effect due to the concentration of HHx units in amorphous regions and suppressive effect due to steric hindrance and hydrophobicity of propyl group. Further, it was validated by the lowest-unoccupied molecular orbital analysis using a semi-empirical molecular orbital calculation method.