Pressure effects on the vibrational spectra of amorphous polystyrene. II. Grüneisen parameters

Mode Gruneisen parameters (γi) of an amorphous polystyrene were determined by measuring the shift of IR absorption frequencies as a function of pressure. It is found that values of γi not only depend on the specific frequency, but also on the volume at which it is determined. Literature data obtained at acoustic frequencies were found to be two orders of magnitude greater than those obtained in this study at IR frequencies. Gruneisen constant γ defined by the macroscopic definition were an order of magnitude greater. It is suggested that there can be many Gruneisen parameters for a given polymer, and that their values depend on the methods of definition and measurement.