Two‐dimensional Fourier transform infrared spectroscopy study of biosynthesized poly(hydroxybutyrate‐co‐hydroxyhexanoate) and poly(hydroxybutyrate‐ co‐hydroxyvalerate)

Generalized two‐dimensional (2D) Fourier transform infrared correlation spectroscopy was used to investigate the effect of the comonomer compositions on the crystallization behavior of two types of biosynthesized random copolymers, poly(hydroxybutyrate‐co‐hydroxyhexanoate) and poly(hydroxybutyrate‐co‐hydroxyvalerate). The carbonyl absorption band around 1730 cm−1 was sensitive to the degree of crystallinity. 2D correlation analysis demonstrated that the 3‐hydroxyhexanoate units preferred to remain in the amorphous phase of the semicrystalline poly(hydroxybutyrate‐co‐hydroxyhexanoate) copolymer, resulting in decreases in the degree of crystallinity and the rate of the crystallization process. The poly(hydroxybutyrate‐co‐hydroxyvalerate) copolymer maintained a high degree of crystallinity when the 3‐hydroxyvalerate fraction was increased from 0 to 25 mol % because of isodimorphism. The crystalline and amorphous absorption bands for the carbonyl bond for this copolymer, therefore, changed simultaneously.