Prof. Dr. Axel Müller

The mechanical performance of immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) (SAN) and the subsequent influence of com-patibilisation by tailored polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock terpolymers (SBM) on the mechanical performance under static and dynamic loads was analysed in detail. The composition of the triblock terpolymers was sys-tematically varied in order to allow evaluation of the influence of the SBM grade and content. With regard to the uncompatibilised PPE/SAN blends, the tensile behaviour of injection-moulded specimens revealed a brittle-to-ductile transition at a composition of 60 wt% of PPE; for this reason, the PPE/SAN 60/40 blend was selected as a base system for the subsequent compatibilisation efforts. The observed static tensile behaviour was described by microme-chanical models and was correlated to the blend microstructures as observed by transmission electron microscopy. In most cases, the addition of the SBM triblock terpolymers further en-hanced the ductility of the blend and, interestingly, only led to a minor reduction of modulus and strength. Triblock terpolymers with symmetric end blocks, mainly located at the interface between PPE and SAN, led to nearly isotropic specimens. In contrast, SBM materials with a longer polystyrene block predominantly formed micelles in the PPE phase and the blends re-vealed a highly anisotropic morphology. Comparative investigations of the fatigue crack growth behaviour parallel to the injection-direction, the weakest link, also reflected this varia-tion in anisotropy of the mechanical behaviour of the compatibilised blends. A poor toughness and a predominant interfacial failure were observed in the case of the SBM with a long poly-styrene block. In contrast, a considerable improvement in properties as a result of pronounced plastic deformations was observed for blends compatibilised by triblock terpolymers with symmetric end blocks. The systematic correlation between morphology and mechanical per-formance of compatibilised PPE/SAN blends established in this study provides an efficient way for the desired selection of suitable and effective SBM compatibilising agents, ensuring both a superior multiaxial toughness as well as a high strength and modulus of the overall system.