The aim of the present work was to investigate the hydrophobicity and polymer compatibility of aminopropylisooctyl polyhedral oligomeric silsequioxane (POSS) - modified Na-montmorillonite (Na-MMT) towards developing polymer-clay nanocomposites. The effect of different concentrations of POSS on properties of Na-MMT was studied. The intercalation ability of the POSS molecules into the Na-MMT interlayer was analyzed by X-ray diffraction. It was found that the d(001) value was increased with increasing the POSS concentration, indicating the successful intercalation of the POSS molecules into the Na-MMT interlayer. The d(001) value was 4.12 nm at 0.4 cation exchange capacity (CEC) loading of POSS, increased at a slight rate upon further increase of CEC loading, and finally reached 4.25 nm at 1.0 CEC loading of POSS. The results of the thermogravimetric (TGA) analysis confirmed the high thermal stability of the POSS-MMT. The thermal stability was defined as a 5% mass loss (T-5) at 0.2 CEC loading of POSS was observed at 352 degrees C and slightly decreased with further increase in the POSS concentration. The porous properties, such as specific surface area (SSA), pore volume, and pore size were estimated by the adsorption of N-2 molecules on the Na-MMT surface. The SSA and pore volume were reduced with increasing the concentration of the POSS molecules due to the adsorption of the POSS molecules on the Na-MMT, while the pore size was increased upon the formation of macroporous structure. The interfacial interaction energy between water and POSS-MMT (Delta G(Clay/Water/Clay)(IF)) was used to evaluate the surface hydrophobicity, and a similar approach was also applied to assess the polymer compatibility of the developed composite. The obtained results confirm that the polymer compatibility of POSS-MMT prepared in this study is better than that of commonly used HDTMA-MMT. (C) 2017 Elsevier Inc. All rights reserved.