Effects of mixing ratio and monomer composition on morphology and mechanical properties of SMI/SAN blends

This article was concerned with the morphology and mechanical properties of blends of poly(styrene-co-N-phenylmaleimide) (SMI) and poly( styrene-co-acrylonitrile) (SAN) as functions of the mixing ratio of the blends and the acrylonitrile content in SAN. Differential scanning calorimetry (DSC) and. field-emission scanning transmission electron microscopy (FE-STEM) were used for the morphology characterization, and tensile strength and K-I (stress intensity factor in mode I), for the mechanical property comparison. The miscibility of the polymers was clearly distinguished using the number of glass transitions shown in the DSC thermograms. FE-STEM supports the DSC results, assisting in understanding the blend morphology for the immiscible blends in terms of the shape and size of the dispersed phase. The mechanical properties suggest that the miscible blends are superior to the immiscible counterparts and illustrate how the acrylonitrile content in SAN and the molecular weights of SMI and SAN affect the toughness of the miscible blends. We conclude from the study that the miscibility between SMI and SAN is an important factor for toughness enhancement of the blends. As a miscible blend, the mechanical properties improve with increase of the acrylonitrile content in SAN and the molecular weight of SMI and SAN. (C) 1998 John Wiley & Sons, Inc.