Compositional analysis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by pyrolysis-gas chromatography in the presence of organic alkali

Copolymer composition of a biodegradable aliphatic copolyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) with a wide range of 3HV contents (ca. 4-23 mol%) was determined by pyrolysis-gas chromatography (Py-GC) in the presence of tetramethylammonium hydroxide (TMAH). Nine major peaks of methylated products, five of which were attributed to the products from 3HV unit and the other four from 3HB unit, were commonly observed in the pyrograms. The copolymer compositions of P(3HB-co-3HV) samples estimated based on the relative intensities of these peaks were consistent with those by 1H NMR. These results demonstrated that Py-GC in the presence of TMAH can be applied to the accurate and highly sensitive compositional analysis of P(3HB-co-3HV) using trace amounts (ca. 0.1 mg or less) of the samples. Furthermore, the fact that a small amount (ca. 1%) of the pyrolyzate from 3HV unit was also observed on the pyrogram of a commercially available poly(3-hydroxybutyrate), PHB, suggested that the given PHB might be actually a copolymer containing minor amount of 3HV unit.