The influence of microstructure on dynamic mechanical behavior in the two phase blend of polycarbonate, (PC), with poly(styrene‐co‐acrylonitrile), (SAN), was studied by comparing the torsional response for injection and compression molded samples. A matrix component's glass transition ( T g ) damping was only moderately altered by the presence of a dispersed phase although shifts in T g , assigned to the local maxima in tan delta, indicated partial miscibility. In compression molded samples the onset of a co‐continuous PC phase suppressed the damping characteristics of the SAN T g on the high temperature side shifting the assignment of this T g to lower temperatures. This suppression results from PC dominating the composite's response at temperatures above the SAN T g . In injection molded samples the onset of PC co‐continuity only partially suppressed the damping of the SAN T g such that a doublet results. Co‐continuity within the injection molded microstructure could be idealized as alternating sheets which, subsequently, in the dynamic mechanical measurement are arranged In series to a shearing stress during torsion. Above the T g of SAN the presence of such a series phase arrangement allows the composite to strain approximately to that extent which would be exhibited by pure SAN alone. The response of the composite is thereby approximately the response of SAN with the almost full extent of its T g damping process realized.
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K. W. McLaughlin (1989) studied this question.
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