radicals or one r8 taken together with the nitrogen atom may form an anilinium radical and r7 is as defined above in the above compounds preferably r7 is a pentafluorophenyl radical in general preferred boron activators may be described as salts of tetra perfluorophenyl boron more specifically the preferred activators are anilinium carbonium oxonium phosphonium and sulfonium salts of tetra perfluorophenyl boron with anilinium and trityl or u201c triphenyl methylium u201d salts being especially preferred it should also be noted that three coordinate boron activators i e compounds of the formula b r7 3 where r7 is as defined above are not suitable for use in the process of this disclosure this is surprising as such compounds are well known as activators for metallocene catalysts however for reasons which are not completely understood the use of a trivalent boron activator is not suitable for preparing polymers having a broad molecular distribution in accordance with the process of this disclosure triethylammonium tetra phenyl boron tripropylammonium tetra phenyl boron tri n butyl ammonium tetra phenyl boron trimethylammonium tetra p tolyl boron trimethylammonium tetra o tolyl boron tributylammonium tetra pentafluorophenyl boron tripropylammonium tetra o p dimethylphenyl boron tributylammonium tetra m m dimethylphenyl boron tributylammonium tetra p trifluoromethylphenyl boron tributylammonium tetra pentafluorophenyl boron tri n butyl ammonium tetra o tolyl boron n n dimethylanilinium tetra phenyl boron n n diethylanilinium.