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 fr equency of various benzonitrile adducts, it is found that the title al uminum compound is a quite weaker Lewis acid than B(C6F5)(3) is, and h as 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 de grees C, it is observed that the C6F5 group was exchanged with the met hyl 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 th at the activity is enhanced with the modification, and the effectivene ss is reduced as modification level is increased. In particular, 7-fol d 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 modifi cation. The modification with B(C6F5)(3) incorporates boron atoms into the oligomeric chain, and is less effective than that with the alumin um analogue. (C) 1998 Elsevier Science B.V. All rights reserved.