Comparison of polymer blends and copolymers by broadband dielectric analysis

Dielectric relaxation measurements on poly o-chlorostyrene (PoCS), polystyr ene (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 temperatur e. The ol-relaxation process associated with micro Brownian motion of the c hain was observed in each sample. The shape of the absorption epsilon "(ome ga) 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 cur ve of the blend relative to the copolymer was well explained by a convoluti on of the individual relaxation processes, which were obtained in the copol ymer by assuming equivalence to an ideal homogeneous mixture of two segment s. The distribution, P(log tau), of the peak position was modeled by a Gaus sian error function. To apply the Vogel-Fulcher equation, the distribution P(T-0) of the Vogel-Fulcher temperature, T-0. was calculated from P(log tau ). To reflect the cooperative motion, T-0 was distributed between the T-0 o f PoCS and that of PS. This is equivalent to assuming that the broadened lo ss peak in the blend is caused by localized concentration fluctuations on t he scale of the segmental motion. The g-factor calculated from the relaxati on strength of the polymer blend was nearly the same as that of PS and of P oCS, but was considerably smaller than that of the copolymer. This differen ce suggests that the local environment of the dipole moment of the chlorost yrene unit in the blend is similar to that of the homopolymer. (C) 2001 Els evier Science Ltd. All rights reserved.