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Low-frequency Raman spectra of a diblock copolymer of polystyrene and polyisoprene (PS−PI) and a polystyrene−polybutadiene blend (PS−PB) have been studied. Low-frequency features, viz., the quasi-elastic lines, Boson peaks, and vibrational lines, if present, have been fitted to known theoretical expressions. It has been found for the first time that, in the diblock, the Boson peaks manifest themselves at frequencies characteristic for homopolymers; that is, big enough regions formed by pure components exist in the diblock. The temperature dependence of the overall integrated intensity in the low-frequency region undergoes a break at the order−disorder transition temperature of the PS−PI diblock and manifests a marked nonlinearity near the temperature of macrophase separation of the PS−PB blend.

Mutual effect of interparticle attraction and repulsion on isotropic Raman line contours and time correlation functions was studied. The theory of Burshtein et al. [Chem. Phys. Lett. 83, 335 (1981); 100, 155 (1983); Spectrochim. Acta 43A, 483 (1987)] was used, and broadening caused by repulsion forces was defined more precisely. The discussion of the results obtained was made with special reference to ionic systems (molten salts and salt glasses).

Repulsional contributions into spectral shifts have been expressed in terms of derivatives of atom displacements with respect to vibrational normal coordinates. Attraction and repulsion have been shown to give a comparable contribution to the overall shift. Working ability of the formulae obtained for spectral shift calculations for molecular (HCl solution in CCl 4 ) and ionic (molten lithium and rubidium nitrates) liquids is demonstrated.