Nanohybrid (phPOSS-f-CNTs) based on Carbon Nanotubes (CNTs) and Phenyl Polyhedral Olygomenric Silsesquioxane (phPOSS) have been synthesized to be used as multifunctional filler for polymer nanocomposites. The success of the functionalization procedure has been demonstrated via accurate spectroscopic, spectrometric and thermo-gravimetric analyses. The results reveal that a large portion of phPOSS is covalently linked to CNTs, while a small amount of phPOSS remains physically adsorbed due to the strong interactions coming from π electron coupling between the CNTs and phenyl rings in phPOSS. Small amounts (1 wt.%) of phPOSS-f-CNTs have been dispersed in Ultra High Molecular Weight Polyethylene (UHMWPE), aiming at improving the photo-stability of the resulting nanocomposite. The rheological and thermo-mechanical behavior of UHMWPE/phPOSS-f-CNTs nanocomposite reflects two …