Silanol polyhedrad oligomeric silsesquiosane terminated with phenyl rings (phPOSS) has been considered as dispersing agent for carbon nanotubes (CNTs) in polyamide (PA) matrix. Two different approaches have been followed for the introduction of the phPOSS molecules: a classical approach which involves the introduction of the dispersing agent during the melt mixing, and an innovative approach, consisting in the immobilization, either covalent and non-covalent, of phPOSS molecules onto CNTs surface. The properties of PA-based nanocomposites, containing free phPOSS molecules and phPOSS molecules immobilized onto the CNTs outer surface, have been evaluated through rheological, mechanical, thermo-mechanical, and morphological analyses. Obtained results highlight the effectiveness of the immobilization of the dispersing molecules onto the surface of the CNTs because of the enhancement of the interfacial interaction between the nanofillers and matrix. The preferential localization of the phPOSS molecules at the interface between the nanofillers and polymer chains helps the CNTs dispersion during melt processing and promote the stress transfer across the interface, leading to the obtainment of nanocomposites with enhanced mechanical performance. POLYM. ENG. SCI., 57:588-594, 2017. (c) 2017 Society of Plastics Engineers