The organically modified montmorillonites (o-MMT) used in this study were prepared in a semi-solid state in molten long chain alkyl (hydrogenated tallow (HT) or stearyl) dimethyl/aryl ammonium chloride intercalant (quat), within a Brabender Plasticorder W50E chamber. The effect of quat level and structure was investigated using WAXS, FTIR (DRIFTS) and solvent swelling/dispersion viscosity studies. It was found that mono-stearyl (or HT) quats were the most suitable intercalants for the in-situ polymerised PS matrix nanocomposites produced. The distearyl (or HT) quats generally led to reduced interfacial effects in the composites and reduced toluene dispersion viscosity due to the close proximity of long alkyl tails within the molecules facilitating their self-assembly into ordered arrays, which were difficult for toluene to penetrate (toluene was used as a probe to gauge compatibility with styrene). Substitution of a benzyl group (for a methyl) led to increased compatibility with styrene/toluene, though the detrimental effect of two long alkyl groups was not overcome. PS matrix nanocomposites have been formed via insitu free radical suspension polymerisation of styrene/organo-montmorillonite (o-MMT) dispersions. These composites displayed evidence of large interfacial area relative to the volume fraction of montorillonite added; this was manifested as a reduction in melt flow rate, broadening of the molar mass distribution (increase in Mw) and an increase in thermal stability, relative to the unfilled matrix. However, wide angle X-ray scattering (WAXS) patterns of the composites revealed a strong (001) reflection (d = 3.3-3.4 nm) together with clear (002) and (003) reflections. Therefore a mixed intercalated/flocculated morphology, with no significant exfoliation into single platelets, was indicated.