Dielectric study of poly(methylacrylate) plus poly(4-hydroxystyrene) or plus poly(4 hydroxystyrene-co-4-methoxystyrene) blends near the glass transition

The dynamics of blends of poly(methylacrylate) (PMA) + poly(4-hydroxystyrene) (P4HS) and poly(4-hydroxystyrene-co-4-methoxystyrene) (MP4HS) have been studied by dielectric relaxation in the frequency range 20 < omega/Hz < 10(5). The results have been analysed in terms of the Havriliak-Negami function plus a conductivity contribution. The time-temperature superposition principle breaks down for the blends, while it seems to be valid for PMA. The width of the relaxation region increases with the content of P4HS or MP4HS, in accordance with previous dynamic mechanical relaxation data. For a given composition, the data of the blends follow the scaling curve proposed by P. W. Dixon (Phys. Rev. Lett., 1990, 42, 8179), however in the low frequency region each sample follows a different scaling curve, which slope is related to the ct parameter of the Havriliak-Negami function. The increase of the width of the relaxation curves with decreasing the PMA content can be well correlated by the coupling model when a gaussian distribution of coupling parameters is taken into account. (C) 1997 Elsevier Science Ltd.