DIFFUSIVE RELAXATION MODE IN POLY(STYRENE-B-METHYLPHENYLSILOXANE) COPOLYMER MELTS ABOVE AND BELOW THE ORDER-DISORDER TRANSITION

Photon correlation spectroscopy in the polarized mode has been used to investigate the dynamics of the composition fluctuations in three poly(styrene-b-methylphenylsiloxane)bulk copolymers. A new diffusive relaxation process has been measured at different temperatures in the disordered (samples S1 and S2) and ordered (S3) state. We interpret the diffusion in S1 and S2 as originating from the relaxation of the equilibrium composition configurations (''pattern'') and the diffusion in S3 as arising from the motion of polystyrene microdomains (cylinders) dispersed in the mobile poly(methylphenylsiloxane) microphase. The vastly different temperature dependence of the pattern and the microdomain diffusion coefficients resemble the temperature dependence of the copolymer zero shear viscosity and the bulk poly(methylphenylsiloxane) viscosity, respectively.