Preparation of Disentangled Ultrahigh-Molecular-Weight Polyethylene by Using Half-Sandwich Titanium Catalysts

Disentangled ultrahigh-molecular-weight polyethylene (dis-UHMWPE) is of fundamental interest and practical importance due to its high crystallinity and facile processing. However, the synthesis of dis-UHMWPE has still been seriously restricted by few catalysts until now, and the molecular weight is limited. Herein, we report the synthesis of a series of half-sandwich titanium complexes and their catalytic performance toward ethylene polymerization activated by less amounts of alkyl aluminum. The catalyst structure (bulky steric hindrance and fluorine atoms on the ligand) and polymerization conditions play important roles in controlling for molecular weight and the disentangled state of polyethylene. The resultant polyethylene showed ultrahigh molecular weight ranging from 3.16 × 10 6 g·mol –1 to 7.15 × 10 6 g·mol –1 with a narrow polydispersity index ( M w / M n < 2.6) and high linearity, and the disentangled state was studied by compression molding and differential scanning calorimetry (DSC) annealing experiments. The formation of active species was also proposed according to electron paramagnetic resonance (EPR) and in situ 1 H NMR experiments.