FTIR Spectroscopic Investigation of the Initiation of Ethylene Polymerization on Cr/Silica

A new chromium(III)/p-tert-butylcalix[4]arene/alkylaluminum catalyst system for the preparation of low molecular weight polyethylene

“…monodentate phenolate ligands [37]. The combinations of chromium(VI)/calix [4]arene and chromium(III)/partially methylated p-tert-butylcalix [4]arene (LH 4 ) were studied by Gibson et al [38] and Floriani et al [39], respectively. Until now, none of them has been reported as a catalyst for ethylene polymerization.…”

“…Until now, none of them has been reported as a catalyst for ethylene polymerization. In our preliminary ethylene polymerization experiments using a chromium(III)/calix [4]arene catalytic combination which was activated by alkylaluminum, the catalyst systems were expected to be specially effective for the preparation of low molecular weight polyethylene by showing an almost homogeneous reaction product, even at high ethylene conversions.…”

“…Despite intense studies, the nature of the active site on the catalyst has remained obscure and the mechanisms of olefin polymerization are still under dispute [1][2][3][4][5][6][7][8][9][10][11]. It is clear, however, that the silica-supported chromium in the hexavalent state is reduced by a reductant, such as CO or ethylene, to a low-valent chromium, which is the active species to polymerize ethylene catalytically [3].…”

“…Their unique structual platform has been utilized to form various complexes with almost all transition metal elements [23][24][25][26][27][28][29][30][31][32][33]; however, only a few of them were considered as homogeneous catalysts for ␣-olefin polymerization [34][35][36]. The early transition metal centers combined by calix [4]arene ligand have been characterized to be more easily coordinated by -donor species such as ethylene compared to the metal centers coordinated by four H 4 L OH OH HO OH Fig. 1.…”

“…The effects of polymerization parameters such as temperature, ethylene pressure, chromium catalyst concentration, type of alkylaluminum compounds, and Al/Cr molar ratio on the catalytic activity and properties of the polyethylene were investigated. The formation of low molecular weight polyethylene using the chromium(III)/p-tert-butylcalix[4]arene/alkylaluminum catalyst system was explained by the coordination effect of structurally hindered and less electron-donating p-tert-butylcalix [4]arene (LH 4 ) anion ligand. …”