MAO-Free polymerization of propylene by racMe(2)Si(1-C5H2-2-Me-4-Bu-t)(2)Zr(NMe2)(2) compound

Ansa-zirconocene diamide complex rac-Me2Si(CMB)(2)Zr(NMe2)(2) (rac-1, CMB = 1-C5H2-2-Me-4-Bu-t) reacts with AlR3 (R = Me, Et, i-Bu) and then with [CPh 3](+) [B(C6F5)(4)](-) (2) in toluene in order to in situ generate cationic alkylzirconium species. In the sequential NNR-scale reactions of rac-1 with various amount of AlMe3 and 2, rac-1 transforms first to rac-Me2Si(CMB)(2) Zr(Me)(NMe2) (rac-3) and [rac-Me2Si(CMB)(2)ZrMe](+) (rac-4) by the reaction with AlMe3, and then to [rac-Me2Si(CMB)(2)ZrMe](+) (5(+)) cation by the re action of the resulting mixtures with 2. The activities of propylene polyme rizations by rac-1/Al(i-Bu)(3)/2 system are dependent on the type and conce ntration of AlR3, resulting in the order of activity: rac-1/Al(i-Bu)(3)/2 > rac-1/AlEt3/2 > rac-1/lMAO much greater than rac-1/AlMe3/2 system. The bul kier isobutyl substituents make inactive catalytic species sterically unfav orable and give rise to more separated ion pairs so that the monomers can e asily access to the active sites. The dependence of the maximum rate (R-p,R -max) on polymerization temperature (T-p) obtained by rac-1/Al(i-Bu)(3)/2 s ystem follows Arrhenius relation, and the overall activation energy corresp onds to 0.34 kcal/mol. The molecular weight (MW) of the resulting isotactic polypropylene (iPP) is not sensitive to Al(i-Bu), concentration The analys is of regiochemical errors of iPP shows that the chain transfer to Al(i-Bu) , is a minor chain termination. The 1,3-addition of propylene monomer is th e main source of regiochemical sequence and the [mr] sequence is negligible , as a result the meso pentad ([mmmm]) values of iPPs are very high ([mmmm] > 94%). These results can explain the fact that rac-1/Al(i-Bu)(3)/2 system keeps high activity over a wide range of [Al(iBu)(3)]/[Zr] ratio between 3 2 and 3,260. (C) 1999 John Wiley & Sons, Inc.