Study of the effect of the nature of catalyst systems on the molecular structure and properties of ultra-high molecular weight polyethylene

Supported catalysts were prepared by interaction of TiCl4 and VOCl3 vapours with surface OH-groups of amorphous SiO2. These catalysts, combined with (C2H5)2AlCl and (C4H9)1,5(C8H17)0.5Mg, are highly active catalyst systems for polymerization of ethylene. It is shown that by careful selection of catalyst concentration and mole ratio of catalyst components in suspension polymerization, ultra-high molecular weight polyethylene (UHMWPE) with molecular weights from 1.2×106 to 5.3×106 can be obtained. Titanium and vanadium containing catalyst systems without carrier was also studied for comparison. The rate of the polymerization process was studied for the catalysts giving high productivity. The slowest polymerization was observed with supported vanadium catalyst and UHMWPE obtained was with molecular weight 5.3×106. The molecular structure of the polymers synthesized was studied by IR spectroscopy after ageing in air. It is shown that the higher content of vinyl groups in UHMWPE synthesized with unsupported titanium catalyst and the higher content of carbonyl groups in UHMWPE with highest molecular weight decreased the thermal stability of the polymers. The thermal and thermodynamic characteristics of the UHMWPE obtained were studied by derivatographic analysis and differential scanning calorimetry. The primary thermooxidative and main chain destruction of UHMWPE obtained with supported titanium catalyst was found to begin at higher temperatures. This determined better physicomechanical properties of the polymers studied.