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

The phase separation behaviors of poly (methyl methacrylate) (PMMA)/ poly (styrene-co-acrylonitrile) (SAN) blends with and without fumed silica (SiO2) have been investigated using time-resolved small-angle light scattering and dynamic rheological measurements. It is found that the effect of SiO2 on the phase separation behavior of PMMA/SAN blend obviously depends on the composition of the blend matrix. The addition of SiO2 causes the cloud point (Tc) and binodal temperature (Tb) to slightly increase for 60/40 PMMA/SAN, and sharply decrease for 30/70 PMMA/SAN. However, the introduction of SiO2 just causes a small increase of the spinodal temperatures (Ts) for PMMA/SAN with all compositions. Hence, the metastable region of 30/70 PMMA/SAN filled with 5 wt% SiO2 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 SiO2 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% SiO2. For such system, the phase separation of the surface layer occurs according to an SD mechanism at relatively low annealing temperatures. The SiO2 particles then act as nuclei, inducing the phase separation of the matrix according to NG mechanism.