STRUCTURAL GRADIENTS DEVELOPED IN INJECTION-MOLDED SYNDIOTACTIC POLYSTYRENE (SPS)

In this experimental research, we investigated the influence of proces sing history on the development of structural gradients in injection-m olded syndiotactic polystyrene (sPS). The structures formed during inj ection molding of this slow-to-crystallize polymer are explained by th e complex interplay between the mechanical history of the sample and t he cooling conditions dictated by such variables as mold temperature, cavity geometry, and injection speed. When crystallized under shear, s PS exhibits unusually high preferential chain orientation along the fl ow direction; this orientation gradually decreases toward the core. Th e mechanical properties are related to the degree of orientation and c rystallinity. (C) 1996 John Wiley & Sons, Inc.