Olefin polymerization catalyzed by amide vanadium(IV) complexes: The stereo‐ and regiochemistry of propylene insertion

Abstract

Abstract The reaction of VCl 3 (THF) 3 with 1 equiv of the lithium salt of ligand ArNH(Me 2 SiCH 2 CH 2 SiMe 2 )NHAr or ArNH(SiMe 3 ) (Ar = 2,6‐Me 2 C 6 H 3 ) afforded the corresponding V(IV) amide complexes, [1,2‐CH 2 CH 2 (Me 2 SiNAr) 2 ]VCl 2 ( 3 ) and (Me 3 SiNAr) 2 VCl 2 ( 4 ). The activation of 3 and 4 with the alkyl aluminum compound Al 2 Et 3 Cl 3 or AlEt 2 Cl produced active ethylene polymerization catalysts exhibiting productivity values among the highest reported for vanadium amide based catalysts. Moreover, syndiotactic specific propylene polymerization was successfully conducted at −40 °C in the presence of 3 /Al 2 Et 3 Cl 3 and 4 /Al 2 Et 3 Cl 3 . Syndiotactic polypropylenes with moderate stereoregularity ([ rr ] = 0.66) and a concentration of regioirregular propylene of 6.9 mol % were obtained. Monomodal molecular weight distributions and polydispersity indices lower than 2 were observed in the polymerization runs carried out in heptane solutions. Thus, ethylene–propylene copolymers with propylene concentrations up to 45 mol % were synthesized and characterized by 13 C NMR and thermal analysis. Good alternation and random distribution of the two monomers were actually obtained. Samples with elevated concentrations of propylene were completely amorphous, with a glass‐transition temperature of −50 °C. The properties and structure of the copolymers produced with amide vanadium catalysts 3 and 4 were similar to those reported for ethylene–propylenes produced with industrial vanadium‐based catalysts, suggesting the presence of the same active catalyst species. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3279–3289, 2006