This article examines the effects of dispersed phase concentration, processing apparatus, viscosity ratio, and interfacial compatibilization using an SAN-amine compatibilizer on the morphology of blends of bisphenol A-polycarbonate (PC) with styrene-acrylonitrile (SAN) copolymers. For uncompatibilized blends, the dispersed phase particle size increased significantly with SAN concentration, and was found to exhibit a minimum at a viscosity ratio of approximately 0.35 for a fixed concentration of 30% SAN in the blend. Although the morphology of uncompatibilized PC/SAN blends mixed in a Brabender mixer, single-and twin-screw extruders were quite similar, the twin-screw extruder produced significantly finer morphologies in blends containing SAN-amine. The average particle size for blends compatibilized with the SAN-amine polymer was approximately half that of uncompatibilized blends and was relatively independent of viscosity ratio and dispersed phase composition.

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The physical approach of blending polymers to develop new or improved polymeric products has been an extremely active area of academic and industrial research for nearly three decades, owing to the much higher costs associated with the alternative of chemical synthesis of new polymers. This activity has been paced by the rapid commercialization of products based on blend technology, including polyamide‐, polyester‐, styrenic‐, vinyl‐, acrylic‐, olefinic‐, and epoxy‐ based materials. The basic principles needed to practice this approach are reviewed, including molecular and thermodynamic factors affecting blend‐phase behavior (miscibility or compatibility), phase morphology, processing, interfacial behavior, and chemical reactions that can occur. General trends and examples of physical properties are given, with special emphasis on the important commercial developments, followed by speculations about future developments.