Filler effects on the phase separation behavior of poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) binary polymer blends

Abstract The phase separation behaviors of poly (methyl methacrylate) (PMMA)/ poly (styrene-co-acrylonitrile) (SAN) blends with and without fumed silica (SiO 2 ) have been investigated using time-resolved small-angle light scattering and dynamic rheological measurements. It is found that the effect of SiO 2 on the phase separation behavior of PMMA/SAN blend obviously depends on the composition of the blend matrix. The addition of SiO 2 causes the cloud point ( T c ) and binodal temperature ( T b ) to slightly increase for 60/40 PMMA/SAN, and sharply decrease for 30/70 PMMA/SAN. However, the introduction of SiO 2 just causes a small increase of the spinodal temperatures ( T s ) for PMMA/SAN with all compositions. Hence, the metastable region of 30/70 PMMA/SAN filled with 5 wt% SiO 2 is expanded in large amplitude by the fillers, while the same region of 60/40 filled PMMA/SAN hardly changes. The selective absorption of PMMA on the surface of SiO 2 results in the difference between the composition of surface layer and that of polymer matrix, especially for 30/70 PMMA/SAN filled with 5 wt% SiO 2 . For such system, the phase separation of the surface layer occurs according to an SD mechanism at relatively low annealing temperatures. The SiO 2 particles then act as nuclei, inducing the phase separation of the matrix according to NG mechanism.