Propylene polymerization withrac-(EBl)Zr(NC4H8)2 cocatalyzed by MAO or AlR3 and anionic compounds

Abstract

Propylene polymerization was carried out using an ansa-zirconocene pyrrolidide based catalytic system of racemic ethylene-1,2-bis(1-indenyl)zirconium dipyrrolidide [rac-(EBI)Zr(NC4H8)2 or (rac-1)] and methylaluminoxane (MAO) or a noncoordinating anion. In situ generation of cationic alkylzirconium species was also investigated by NMR-scale reactions of rac-1 and MAO, and rac-1, AlMe3, and [Ph3C] [B(C6F5)4]. In the NMR-scale reaction using CD2Cl2 as a solvent, a small amount of MAO ([Al]/[Zr] = 30) was enough to completely activate rac-1 to give cationic methylzirconium cations that can polymerize propylene. The resulting isotactic polypropylene (iPP) isolated in this reaction showed a meso pentad value of 91.3%. In a similar NMR-scale reaction rac-1 was stoichiometrically methylated by AlMe3 to give rac-(EBI)ZrMe2, and the introduction of [Ph3C] [B(C6F5)4] into the reaction mixture containing rac-(EBI)ZrMe2 led to in situ generation of cationic [rac-(EBI)Zr(μ-Me)2AlMe2]+ species that can polymerize propylene to give iPP showing a meso pentad value of 94.7%. The catalyst system rac-1/MAO exhibited an increase of activity as the [Al]/[Zr] ratio increased within an experimental range ([Al]/[Zr] = 930–6511). The meso pentad values of the resulting iPPs were in the range of 83.2–87.5%. The catalytic activity showed a maximum (Rp = 6.66 × 106 g PP/mol Zr h atm) when [Zr] was 84.9 × 10−6 mol/L in the propylene polymerization according to the concentration of catalyst. MAO-free polymerization of propylene was performed by a rac-1/AlR3/noncoordinating anion catalytic system. The efficiency of AlR3 was decreased in the order of AlMe3 (Rp = 13.0 × 106 g PP/mol Zr h atm) > Al(i-Bu)3 (8.9 × 106) > AlPr3 (8.8 × 106) > Al(i-Bu)2H (8.4 × 106) > AlEt3 (8.4 × 106). The performance of the noncoordinating anion as a cocatalyst was on the order of [HNMePh2][B(C6F5)4] (Rp = 13.0 × 106 g PP/mol Zr h atm) > [HNMe2Ph][B(C6F5)4] (10.8 × 106) > [Ph3C][B(C6F5)4] (8.4 × 106) > [HNEt2Ph][B(C6F5)4] (7.8 × 106). The properties of iPP were characterized by 13C-NMR, FTIR, DSC, GPC, and viscometry. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 875–885, 1999