The fluorinated bis(phenoxyimine)Ti complexes (FI catalyst) are immobilized onto the polyhedral oligomeric silsesquioxane (POSS)-modified silica for the preparation of ultrahigh molecular weight polyethylene (UHMWPE) with a weakly entangled state. The POSSs can assemble to spherical nanoaggregates with an average size of 60 nm, which can serve as isolators to separate the active species and growing chains. The weakly entangled UHMWPE is prepared with an exceptional activity owing to this isolation. The evolution of entanglements for polymer chains is studied based on the fragmentation of catalytic particles. It is evidenced by the results of polymerization and characterization that 30 min of polymerization is the critical time for the entire fragmentation of catalytic particles. Importantly, this fragmentation leads to a rupture of the reacted environment which is established by the POSS nanoaggregates. Further polymerization will synthesize the UHMWPE with more entangled density.