Ziegler–Natta catalysts on silica for ethylene polymerization

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Abstract
The amount of dibutylmagnesium (DBM) or triethylaluminum (TEAL) that reacted with silica at 55–60°C depended on the silica calcining temperature. Lower silica calcining temperatures resulted in more Mg or Al fixed to the silica surface, indicating greater amounts of DBM or TEAL reacting with the silica. The amount of the metal alkyls butyl(octyl) magnesium ethoxide, ethylaluminum dichloride, tri‐n‐hexylaluminum, and diethyl(ethyldimethylsilanolato) aluminum that reacted with 600°C calcined silica was also determined. The metal alkyl can react with the silica at two sites, a surface hydroxyl group and a siloxane group. The silica surface hydroxyl groups can be chemically converted to trimethylsilyl groups so that only the siloxane groups are available for attack. After the metal alkyl was reacted with silica, the resulting intermediate was treated with titanium tetrachloride to yield an ethylene polymerization catalyst in the presence of TEAL. When no metal alkyl was employed, titanium tetrachloride reacted only with the silica surface hydroxyl groups to yield a weakly active ethylene polymerization catalyst.