Toughening of SMA copolymers with an SAN‐grafted rubber

Styrene/maleic anhydride (SMA) copolymers were toughened by blending with a styrene/acrylonitrile (SAN) grafted rubber. The AN content of the SAN graft was fixed at 22.5% and the MA content of the SMA matrix was varied from 8 to 25%. The maximum impact strength was observed for blends based on SMA copolymers containing 14–17% MA (depending on the rubber content). These compositions are near the boundary of miscibility between the SMA matrix and SAN graft since miscibility of SMA and SAN occurs when the MA and AN contents are about the same in each Dilatational processes were shown to be the major mechanism of defor‐mation for these blends. Scanning electron microscopy was used to observe fracture surfaces as the miscibility between SMA and SAN or as the rubber content was changed. Toughening of miscible SMA/SAN matrices by this impact modifier was also examined. The results are discussed in terms of a variety of possible contributing factors including the coupling of the rubber to the matrix via miscibility of the latter with the SAN graft.