[3-t-Bu-2-O-C6H3CH=N(C6F5)](2)TiCl2 catalyst (FI catalyst) was immobilized on disilanolisobutyl POSS to synthesize disentangled ultra-high molecular weight polyethylene (UHMWPE)/POSS nanocomposites during ethylene in situ polymerization. The presence of POSS significantly influenced the polymerization properties of the FI catalyst active centers. It was shown that the characteristic of "living" polymerization of the FI catalyst was retarded. Furthermore, disilanolisobutyl POSS is dispersed uniformly in the UHMWPE matrix with particles size of only several tens nanometers. Interestingly, the incorporation of the POSS into nascent UHMWPE matrix led to a strong interaction between the POSS particles and the UHMWPE chains, resulting in an increased density of entangled chains, as reflected by theological test. Moreover, the crystallinity and the lamellae thickness of nascent UHMWPE increased upon increasing POSS loading, as observed by differential scanning calorimetry. It suggested that the POSS particles would be presented as a nucleating agent. Finally, the thermal stability and the hydrophilic property of the nanocomposites were improved due to the incorporation of POSS particles. (C) 2014 Elsevier Ltd. All rights reserved.