A Polyhedral oligomeric silsesquioxane (POSS) modified Ziegler-Natta catalyst is reported to synthesize the weakly entangled ultra-high molecular weight polyethylene at a high temperature and with a high activity. Incorporation of POSS can form numbers of aggregates with a mean size of 48 nm adsorbing on the surface of SiO2. The structure of nanoaggregates is evidenced by the experiments and theoretical calculations where one POSS can coordinate with multiple MgCl2 molecules serving as an electric donor to the further immobilized TiCl4. The catalyst is thus featured by two distinct active regions positioned in the POSS/MgCl2 nanoaggregates and delta-MgCl2, respectively. The former regions present extremely low activity on ethylene polymerization, which function as horizontal separators for isolating the active TiCl4 sites and the growing chains. This catalyst exhibits an exceptional activity (i.e. 1.3 x 10(6) gPE mol(Ti)(-1) h(-1) bar(-1)) for the synthesis of weakly entangled polyethylene at 60 degrees C. (C) 2018 Elsevier Inc. All rights reserved.