Intermolecular interactions of poly(3-hydroxybutyrate -co-3-hydroxyvalerate) (P(HB- co-HV)) with PHB-type crystal structure and PHV-type crystal structure studied by low-frequency Raman and terahertz spectroscopy

摘要

AbstractComposition-, temperature-, and polarization-dependent low-frequency Raman and terahertz (far-infrared; FIR) spectra were measured for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) with PHB-type crystal structure and PHV-type crystal structure to investigate their intermolecular interactions. Band assignments were attempted by comparing the low-frequency Raman and terahertz (FIR) spectra of P(HB-co-HV) with the varying HV content with the corresponding spectra of PHB and by observing spectral variations. The spectra of P(HB-co-HV) (HV?=?9, 15, and 21?mol%) are similar to the corresponding spectra of PHB. There are two bands at 97 and 82?cm?1which are assigned to a spring type vibrational mode of the helical structure and to the mode reflecting the intermolecular interaction (CH3?O=C hydrogen bond), respectively. The low-frequency Raman and terahertz spectra of P(HB-co-HV) with HV content of 66 and 88.6?mol% show bands at 91 and 78?cm?1. The 78?cm?1band is assigned to the intermolecular interaction (CH2?O=C hydrogen bond). In contrast to the 97?cm?1band of P(HB-co-HV) with the low HV content, the 91?cm?1band of P(HB-co-HV) with the high HV content show a temperature-dependent shift by 4?cm?1. Thus, although it seems that both 97 and 91?cm?1