Comparison of polymer blends and copolymers by broadband dielectric analysis

Dielectric relaxation measurements on poly o-chlorostyrene (PoCS), polystyrene (PS), a 50 mol% PoCS/PS blend, and a 50 mol% P(oCS/S) random copolymer were made in the frequency range 1 mHz to 1 MHz as a function of temperature. The α-relaxation process associated with micro Brownian motion of the chain was observed in each sample. The shape of the absorption ϵ″(ω) of the copolymer was nearly the same as that of PS and of PoCS, and was considerably narrower than that of the blend. The broadened relaxation curve of the blend relative to the copolymer was well explained by a convolution of the individual relaxation processes, which were obtained in the copolymer by assuming equivalence to an ideal homogeneous mixture of two segments. The distribution, P(log τ), of the peak position was modeled by a Gaussian error function. To apply the Vogel–Fulcher equation, the distribution P(T0) of the Vogel–Fulcher temperature, T0, was calculated from P(log τ). To reflect the cooperative motion, T0 was distributed between the T0 of PoCS and that of PS. This is equivalent to assuming that the broadened loss peak in the blend is caused by localized concentration fluctuations on the scale of the segmental motion. The g-factor calculated from the relaxation strength of the polymer blend was nearly the same as that of PS and of PoCS, but was considerably smaller than that of the copolymer. This difference suggests that the local environment of the dipole moment of the chlorostyrene unit in the blend is similar to that of the homopolymer.