Abstract
The lower critical solution temperature ( LCST) type phase behaviour of a poly(styrene- co-acrylonitrile)/ polycarbonate blend was verified by time-resolved light scattering analysis of the kinetics of both phase separation (above LCST) and phase dissolution (below LCST). The diffusion coefficient for separation was much larger than that of dissolution. The kinetic results provided a plausible scenario for the development of bicontinuous two-phase structure in the melt-processed blend as follows. When cold pellets of both polymers are heated to above the glass transition temperature ( T g) of the polymers in the extruder, dissolution starts. Even after attaining the spinodal temperature ( T s = 223°C) dissolution continues, since T s can be elevated under shear to above the barrel temperature (260°C). The homogeneous melt is extruded and quenched quickly into water. When the single-phase blend is heated under high shear in an injection machine (at 290°C) and injected into a cold mould, spinodal decomposition proceeds until the melt is cooled down to T s. The dissolution below T s is negligible so that the bicontinuous structure attained via spinodal decomposition is frozen in the moulded blend by vitrification near T g.
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