The potential of polystyrene/polymethylphenylsiloxane (PS/PMPS) blends as a matrix for nanocomposites is investigated. It was proven by dynamic rheometry and conductivity measurements that PMPS effectively disperses carbon nanotubes, as was already known for polydimethylsiloxane (PDMS). The phase behaviour of PS/PMPS blends was investigated using differential scanning calorimetry or modulated temperature differential scanning calorimetry. The blends were found to exhibit partial miscibility, in contrast to the known immiscible behaviour of PS/PDMS blends. A miscibility window exists for PS/PMPS blends containing less than approximately 10 wt% PMPS.