UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization

Different nanocomposites have been attained by in situ polymerization based on ultra-high molecular weight polyethylene (UHMWPE) and mesoporous SBA-15, this silica being used for immobilization of the FI catalyst bis [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium (IV) dichloride and as filler as well. Two distinct approaches have been selected for supporting the FI catalyst on the SBA-15 prior polymerization. A study on polymerization activity of this catalyst has been performed under homogenous conditions and upon heterogenization. A study of the effect of presence of mesoporous particles and of the immobilization method is also carried out. Moreover, the thermal characterization, phase transitions and mechanical response of some pristine UHMWPEs and UHMWPE/SBA-15 materials have been carried out. Relationships with variations on molar mass, impregnation method of catalyst and final SBA-15 content have been established

Synthesis of high molecular weight polyethylene using FI catalyst

A FI Zr-based catalyst of bis[N-(3,5-dicumylsalicylidene)-2′,6′­diisopropylanilinato]zirconium(IV) dichloride was prepared and used for polymerization of ethylene. The effects of reaction conditions on the polymerization were examined in detail. The increase in ethylene pressure and rise in polymerization temperature up to 35 oC were favorable for catalyst/MAO to raise the catalytic activity as well as the viscosity-average molecular weight (Mv) of polyethylene. The activity of the catalyst was linearly increased with increasing MAO concentration and no optimum activity was observed in the range studied. Although introduction of the bulky cumyl and 2′,6′-diisopropyl alkyl substitution groups on ortho positions to the phenoxy-oxygen and on phenyl ring on the N, respectively enhanced the viscosity average molecular weight (Mv) of the obtained polymer strongly, diminished the activity of the catalyst. Neither the activity of the catalyst nor the (Mv) of the obtained polymer were sensitive to hydrogen concentration. However, higher amount of hydrogen could slightly increase the activity of the catalyst. The (Mv) of polyethylene ranged from 2.14×106 to 2.77×106 at the monomer pressure of 3 and 5 bar respectively which are much higher than that of the reported FI Zr-based catalysts