Anion Effects on the Activity and Stereoselectivity in Propene Polymerisations Catalyzed by C₂‐Symmetric and “Oscillating” Catalysts

Abstract

Summary: The influence of perfluoroborate anions on catalyst activity and stereospecificity has been determined for propene polymerisations at 20–60 °C. For C2‐symmetric ansa‐zirconocenes, activities were strongly ligand‐dependent, with systems activated by TIBA/Ph3C+X−, where TIBA = AliBu3, X = {Z[B(C6F5)3]2}, and Z = CN or NH2, giving significantly higher activities than methylaluminoxane under comparable conditions. For high‐activity catalysts at 60 °C, {H2N[B(C6F5)3]2}− proved superior to {CN[B(C6F5)3]2}−, presumably due to the higher thermal stability of the amidoborate. The influence of counteranions on PP stereospecificity for these catalysts is negligible. On the other hand, the conformationally flexible catalyst, (2‐PhInd)2ZrCl2/TIBA/Ph3C+X−, shows not only a strong anion dependence of its activity, but also significant variation in poly(propylene) isotacticity, mainly due to the formation of small fractions of highly isotactic (mmmm > 70%) PP. This effect was particularly pronounced for {CN[B(C6F5)3]2}− and the dianion, {Ni[CNB(C6F5)3]4}2−.Effect of {CN[B(C6F5)3]2}− and {H2N[B(C6F5)3]2}− on propene polymerisation productivities for zirconocenes 1–8 at 20 °C.imageEffect of {CN[B(C6F5)3]2}− and {H2N[B(C6F5)3]2}− on propene polymerisation productivities for zirconocenes 1–8 at 20 °C.

Kinetic and mechanistic aspects of metallocene polymerisation catalysts

“…An example are the complexes [77,78]. There is no detectable effect of the counteranion on polypropenes produced with C 2 -symmetric ansa-zirconocenes [62,79]. For the C s -symmetric complex 21, on the other hand, there is a pronounced increase in stereoselectivity with tighter ion pairing.…”

“…While at 25°C the cyano-bridged anion [CN{B(C 6 -F 5 ) 3 } 2 ] À was found to give the highest propene polymerisation activities, at 60°C [H 2 N{B(C 6 F 5 ) 3 } 2 ] À proved superior, probably do to its greater thermal stability [62].…”

Recent research progress in influence of the ansa-zirconcene catalytic system on the polypropylene microstructure

“…Ansa-metallocenes of C 2 -symmetry can ensure the synthesis of iPP (isotactic polypropylene) and atactic PP, those of C 1 -symmetry provide hemi-isotactic, isotactic or stereoblock PP that depend on the type of ligands and substituents of them and those of C s -symmetry can lead to the synthesis of syndiotactic PP [11,12]. Scheme 3.…”

“…Complex 8 activated by CN[B(C 6 F 5 ) 3 ] 2 is of very high stereoselectivity and brings about isotactic PP (mmmm = 97%), because the t-butyl substituent on the 3,3 -position of ansa-bisindenyl zirconium has a great steric effect to the enantiomorphic site. Trimethylsilyl groups and t-butyl on 3,3 -position of the two cyclopentadienyl ligands (9,11) also lead to high stereoselectivity [11,12].…”

Propylene Polymerization Using ansa‐Zirconocenes with Water/Pentafluorophenol‐Modified Methylaluminoxane

“…[11][12][13][14][15][16][17][18][19][20] Recently, several research groups have studied the effect of the cocatalyst on the stereoregularity of propylene polymerization. [17,21,22] We have reported the enhancement of productivity, stereoregularity, and regioregularity as well as increased molecular weight of 1-butene polymerization with a 2,2-thiobis(phenoxy)titanium complex (1) [23][24][25][26] by isobutylmethylaluminoxane (MMAO) modification using water [27] or both water and pentafluorophenol. [28] In these studies, we claim that the addition of water and pentafluorophenol induces the structural and electrical changes in the aluminoxane and the reduction of ''free'' trimethylaluminum (TMA).…”