Early Stages of Ethylene Polymerization Using the Phillips CrO_x/Silica Catalyst

Abstract

The reaction of ethylene with CO prereduced CrO x /silica polymerization catalyst has been monitored by quadrupole mass spectrometry. Evolution of 1-hexene is observed shortly after ethylene adsorption. This corresponds to the formation of a chromacyclopentane intermediate species which can also participate in ethylene polymerization.

Enhancing the Initial Rate of Polymerisation of the Reduced Phillips Catalyst by One Order of Magnitude

“…[1, 11b, 13,14] The above-mentioned induction period becomes a problem when ethylene polymerisation must be performed at a lower temperature (e.g., for production of ultra-high-molecular-weight polyethylene).…”

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

“…In the presence of ethylene,t he reduced Cr II site is proposed to form Cr IV -alkyl complexes that could coordinate and insert ethylene (Scheme 17). [259,[273][274][275][276][277][278][279][280] Another possibility is the oxidative coupling of ethylene on aC r II site to form aC r IV -metallacyclopentane (Scheme 17) [262,281] that can grow into ap olymer by ring expansion [282] or by b-H elimination to form aC r IV -allyl hydride (SiO) 2 Cr(H)(h 3 -allyl) that is able to insert ethylene and start polymer growth. Insertion of ethylene in either the Cr-vinyl or the Cr À Hb ond of this species can initiate the polymerization.…”

Cr Complexes of Nitrogen Donor Ligands for Olefin Oligomerisation and Polymerisation

“…This catalyst has been used on great industrial scale for over half a century; however, despite this the mechanism of chain growth is still uncertain. There is no doubt some evidence for a metallacycle mechanism [3,[103][104][105]. There seems to be no obvious reason why large ring metallacycles could not grow to high molecular weight polymer.…”