In this experimental research, we investigated the influence of processing history on the development of structural gradients in injection-molded syndiotactic polystyrene (sPS). The structures formed during injection molding of this slow-to-crystallize polymer are explained by the complex interplay between the mechanical history of the sample and the cooling conditions dictated by such variables as mold temperature, cavity geometry, and injection speed. When crystallized under shear, sPS exhibits unusually high preferential chain orientation along the flow direction; this orientation gradually decreases toward the core. The mechanical properties are related to the degree of orientation and crystallinity. © 1996 John Wiley & Sons, Inc.