Dielectric segmental mode relaxation (the R-relaxation) was investigated for toluene solutions of poly(vinyl acetate) (PVAc) and for undiluted PVAc. The relaxation spectra in concentrated solutions were found to be much broad compared with those in the undiluted state and in dilute solution. It was also found that the relaxation spectra broadened with decreasing temperature near the glass transition temperature. For concentrated solutions, the correlation length of local heterogeneity (due to concentration fluctuation) was determined to be 1.0 nm by using small-angle X-ray scattering. On the basis of the assumption that the distribution of relaxation times in logarithmic scale is proportional to the magnitude of the heterogeneity, the temperature dependence of the broadness of loss curves can be explained. Thus, the broad dielectric relaxation spectra in concentrated solutions can be attributed to a local configurational irregularity of the polymer segments and the solvent molecules.

The effect of local heterogeneity on the distribution of dielectric relaxation times was studied for concentrated solutions of poly(vinyl acetate) (PVAc) in 1-methylnaphthalene (MN) and those of poly-(vinyl octanoate) (PVOc) in toluene (Tol). The half-widths Λ of the dielectric loss curves for the primary processes of those systems are compared with those of the PVAc/Tol system reported previously. The data indicate that Λ decreases in order of PVAc/Tol, PVAc/MN, and PVOc/Tol systems if compared at the same temperature T/T g where Tg denotes the glass transition temperature of solutions. The halfwidth of each solution increases with decreasing temperature. The loss curve is calculated by assuming a Gaussian distribution of the local concentration φ which results in the distribution of relaxation times g(τ). The calculated loss curves agree fairly well with the observed ones. The broadening behavior is also explained by assuming that Λ is proportional to the amplitude of the local concentration fluctuation ∆φ times the slope of the φ dependence curve of the average relaxation time τ. This assumption leads to a linear relationship between Λ and ∆φ/(T -T 0) 2 where T0 is the Vogel critical temperature. Using this relation, we have attempted to estimate ∆φ. Small-angle X-ray scattering was also measured on PVAc/ MN solutions and found that the scattering intensity was lower than that for PVAc/Tol. This is consistent with the fact that Λ of PVAc/MN solutions is narrower than PVAc/Tol solutions.