Preparation of Al(C6F5)3 and its use for the modification of methylalumoxane

Tris(pentafluorophenyl)aluminum was prepared from a metathesis between AlMe3 and B(C6F5)(3) in a quantitative yield. Out of CN stretching frequency of various benzonitrile adducts, it is found that the title aluminum compound is a quite weaker Lewis acid than B(C6F5)(3) is, and has rather similar acidity as AlMe3. When mixtures of methylalumoxane (MAO) and Al(C6F5)(3).(toluene)(0.5) or B(C6F5)(3) were heated at 65 degrees C, it is observed that the C6F5 group was exchanged with the methyl group of the MAO. Several MAOs were prepared with variable degrees of modification. Catalytic activity of pristine MAO and modified MAOs were tested for ethylene and propylene polymerization. It is found that the activity is enhanced with the modification, and the effectiveness is reduced as modification level is increased. In particular, 7-fold increase of activity for polyethylene is observed, when 5.5 x 10(-3) equimolar amount of Al(C6F5)(3).(toluene)(0.5) is used for the modification. The modification with B(C6F5)(3) incorporates boron atoms into the oligomeric chain, and is less effective than that with the aluminum analogue. (C) 1998 Elsevier Science B.V. All rights reserved.