Profiles of ethylene polymerization with zirconocene-trialkylaluminum/borane compound

Ethylene polymerization was conducted with bis(cyclopentadienyl)zirconium d ichloride (1) and rac-dimethylsilylenebis(indenyl)zirconium dichloride (2) combined with trialkylaluminum (AlR3; R = methyl (Me), ethyl (Et), isobutyl (iBu))/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)(4 )) or tris(pentafluorophenyl)borane (B(C6F5)(3)) to study the effect of coc atalysts on polymerization rate (R-p). When AlMe3 was used, no activity or very low activity was observed with both zirconocenes regardless of the bor ane compounds used. The replacement of AlMe3 to AIEt(3) or AliBu(3) with 1- AlR3/Ph3CB(C6F5)(4) caused polymerization and induction time was observed t o reach the maximum R-p. Especially in the case of using AlEt3, it took abo ut 30 min to show the activity. When B(C6F5)(3) was used, AlEt3 was not eff ective but AliBu(3) gave the highest activity among all the combinations of AlR3 and the borane compounds. In the case of polymerization with 2 using Ph3CB(C6F5)(4), high activity was observed with both AlEt3 and AliBu(3) wit hout any induction period. When B(C6F5)(3) was used instead of Ph3CB(C6F5)( 4) very low activity was observed with AlEt3. On the other hand, high activ ity was observed with AliBu(3), and the maximum R-p was found at the beginn ing of the polymerization. The effect of AlR3 on the formation of active sp ecies was discussed based on these results. (C) 1999 Elsevier Science B.V. All rights reserved.