The high temperature application of styrenic polymers was extended beyond the glass transition temperature of amorphous PS by the two following modifications: 1. Increasing the syndiotactic portion, producing crystallites, which act as physical cross-links in the temperature region between the glass transition and the melting point. 2. Copolymerisation with DPE leading to an increase in the glass transition temperature with increasing DPE-content. In both materials crazing prevails. Toughness has been successfully improved by rubber modification, by which the initiation and stabilisation of the deformation processes-mostly voiding and crazing-are enhanced. Due to the higher stiffness of the molecules in S/DPE and the mutual interaction between the propagating crazes and the crystalline lamellae in sPS, the rubber toughening in these two types of products is likely to be reduced compared to an amorphous PS.