Low-Frequency Vibrational Motions of Polystyrene in Carbon Tetrachloride: Comparison with Model Monomer and Dependence on Concentration and Molecular Weight.

In this study, the low-frequency vibrational dynamics of polystyrene (PS) in CCl was investigated by femtosecond Raman-induced Kerr effect spectroscopy. Ethylbenzene (EBz) was also investigated as a model monomer of the polymer to elucidate the unique dynamical features of PS in solution. The broadened low-frequency spectrum of the PS/CCl in the frequency region below 150 cm is significantly different from that of the EBz/CCl. Difference spectra between the PS or EBz solutions and neat CCl, normalized to an internal vibrational mode of CCl, clearly show a much lower spectral intensity for the PS/CCl than the EBz/CCl in the low-frequency region below ca. 20 cm. This indicates that translational motions are suppressed in the PS/CCl compared to the EBz/CCl. Moreover, the high-frequency motion at ca. 70 cm, mainly due to phenyl ring librations, occurs at higher frequency in PS (78 cm) than EBz (65 cm). In addition, the results of concentration-dependent experiments show that the first moment () of the low-frequency difference spectra of both PS/CCl and EBz/CCl is almost independent of the concentration. The molecular weight dependence of the low-frequency spectrum in the PS/CCl shows that the value of the low-frequency spectral band of PS shifts to higher frequencies when the molecular weight of PS increases up to = ∼1000, which corresponds approximately to the decamer, and then remains constant upon further increasing the molecular weight.