Ethylene Polymerizations with Alkyl-, Disilylamino- and Cyclopentadienylchromium/MMAO Initiators

Abstract

The catalytic activities of non‐metallocene type chromium, half‐sandwich type chromium and metallocene type chromium complexes for the polymerization of ethylene were explored using MAO, modified MAO (MMAO) or BuAO in the presence or absence of a silica support. The complexes, Cr[N(SiMe3)2]3 (1), Cr[CH(SiMe3)2]3 (2), Cr(CH2SiMe3)4 (3), and Cr(CH2CMe3)4 (4), displayed good catalytic activities for the polymerization of ethylene in the presence of excess MAO or MMAO. The activities exceed 103 g‐PE/Cr‐mol·h to lead to polymers with Mw > 80×104. The molecular weight distributions are rather narrow in cases of complexes 1 and 2. More efficient catalysis was observed when C5Me4‐CH2CH2NMe2CrCl2 (5) and C5H4CH2CH2N(iPr)2CrCl2 (6) were used coupling with MMAO in the presence of a silica support. The Mw increased to 276.2×104 and the Mw/Mw value decreased into 2.2 in the case of complex 5. The catalysis of (C5H5)2Cr (7) in the presence of a silica support is very high and the complex (7) produced high molecular weight polyethylene with narrow molecular weight distribution, while [1,3‐(SiMe3)2C5H3]2Cr (8) shows only a little catalytic activities presumably due to its very weak interaction with a silica support.

Ethylene Polymerization with Silica-Supported Cr[N(SiMe3)2]3/Alumoxane Catalyst

“…reacting anhydrous CrCl 3 with (Me 3 Si) 2 NLi in tetrahydrofuran and obtained as bright green crystals. 23 The detail procedure of the synthesis and results of elemental analysis and mass spectrum measurement are described in ref 23. The crystals were dissolved and diluted by hexane to prepare the 0.1 M Cr[N(SiMe 3 ) 2 ] 3 stock solution.…”

New divalent samarocenes for butadiene polymerisation: influence of the steric effect and the electron density on the catalytic activity

“…The divalent lanthanocenes are not active either [7], because of the formation of a stable Ln(III)(g 3 -allyl) complex [8]. Very recently, Wakatsuki and his co-workers [9] reported that polymerisation of butadiene was possible with Cp à 2 Sm(THF) 2 (3) activated by aluminium derivatives: MMAO (modified methylaluminoxane containing both isobutyl and methyl groups [10]) or AlR 3 /[Ph 3 C][B(C 6 F 5 ) 4 ] (R¼ Me, Et, i Bu). The authors obtained regular cis-1,4 polybutadiene and discussed the reactivity of the catalytic system in regard to the nature of the aluminium reagent.…”

Immobilization and Activation of a Single‐Site Chromium Catalyst for Ethylene Polymerization using MgCl2/AlRn(OEt)3 − n Supports

“…An activity of 2 889 kg Á (mol Cr) À1 Á bar À1 Á h À1 was obtained at around 30 8C under homogeneous polymerization conditions, which is significantly higher than the activities later reported by Yasuda et al for the same complex activated using MAO under homogeneous conditions or on a silica support. [12] Related half-sandwich cyclopentadienylchromium complexes have very recently been reported by Huang and coworkers. [13] In the present work we have investigated the immobilization and activation of the chromium complex 1, making use of MgCl 2 /AlR n (OEt) 3 À n supports prepared by the reaction of an adduct of composition MgCl 2 Á 1.1EtOH with different aluminium alkyls.…”