We demonstrated the compatibilizing effect of graphene oxide (GO) in the immiscible poly(methyl methacrylate)/polystyrene (PMMA/PS, 80/20) blend and showed that such a compatibilizing effect was affected by the processing temperature. For the blends prepared at a relatively low temperature (190 °C), the incorporation of 0.5 wt% of GO results in a dramatic reduction in the domain diameter of dispersed minor phase (PS), indicating that GO is an effective compatibilizer. Increasing the processing temperature decreases the dispersed phase size reduction, illustrating that the compatibilizing effect of GO is adverse to processing temperature. The characterization results including the changes in chemical composition of GO and morphologies evolution of blends at different annealing temperatures reveal that this temperature-dependent compatibilizing effect should be attributed to the in situ thermal reduction of GO during the melt processing, which breaks the hydrophilicity-hydrophobicity balance of GO and renders it more hydrophobic. A comparative experiment shows that chemically reduced GO has almost no compatibilizing effect for PMMA/PS blends, which further confirms the proposed mechanism. In addition, the GO-compatibilized blends exhibit great improvement in the mechanical properties than uncompatibilized blends.

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