Vanadium and Chromium Catalysts for Polymerization of Ethylene

Abstract

In the present progress report literature data concerning homogeneous catalyst systems based on vanadium and chromium are reviewed and complemented by a combined study of the magnetic properties and the polymerization activity of such systems. The results show that vanadium forms active species as V ( I I I ) and as V ( I I ) , but chromium only as Cr ( I I ) ; models are suggested for the polymerization process.-A comparison with heterogeneous systems (Phillips catalyst) allows the establishment of some general principles concerning the activity of the catalyst and the properties of the polymers.Angew. Chem. internat. Edit. Vol. 10 (1971) / No. I I

Catalytic Olefin Polymerization

“…Soluble catalytic systems are also obtained by reaction of Ti(acac)3 [43] and Cr(acac)3 [44] with AIE~ as well as by reaction of Cr(acac)3 and VO(acac)2 with AlEt 2 CI in the presence of triethyl phosphite [45]. In the last case, the catalytic activity reaches its maximum at AIN ratio = 50.…”

“…a) Ziegler-Natta soluble catalysts The catalytic system CP2 TiCI 2 -AlEt 2 CI is thoroughly soluble and, after a short induction time, exhibits an elevated efficiency in the initial 2-3 minutes (1.5 x 10-3 mol dm-3 S-l; [Ti] = 3 x 10-3 mol dm- 3 ; [AI] = 6 x 10-3 mol dm -3; [C 2 H 4 ] = 10.4 x 10-2 mol dm -3) followed by quick deactivation probably due to side reactions [33]. 293 293 303 [33] [32] [35] [37] [39] [45] [45] The activity of these' catalytic systems is considerably enhanced by the addition of small quantities of water to the Al alkyl compound (Table 3).…”

Coordination Polymerization

“…Before insertion, the double bond in the olefin monomer coordinates to the coordination vacancy of the transition metal. After the olefin is inserted into the growing polymer chain, another olefin monomer can coordinate to the vacant site; thus the process of insertion is repeated to increase the size of the polymer chain by one monomer unit at a time until chain transfer takes place [17]. In the case of copolymerization, there is a competition between the comonomers to coordinate to the active sites and to be inserted into the growing polymer chains.…”

Effect of Alkyl Aluminums on Ethylene Polymerization Reactions with a Cr‐V Bimetallic Catalyst

“…Compared with the Cr/SiO 2 system, vanadium‐based catalysts allows the preparation of high‐MW polymers with narrow MWD and high a‐olefin incorporation, but very low activity due to the deactivation during catalysis by reduction of active vanadium species to low‐valent, less active or inactive species . Henrici‐Olivé et al reported that both V(III) and V(II) species were active for ethylene polymerization in a homogenous system with aluminum alkyl, but the increase of Al/V favored the V(III) in the equilibrium reaction of V(II) and V(III) . Czaja and Bialek reported a high activity and stability of the vanadium catalyst supported on magnesium complex with diethylaluminum chloride as cocatalyst.…”

“…[38][39][40] Henrici-Olivé et al reported that both V(III) and V(II) species were active for ethylene polymerization in a homogenous system with aluminum alkyl, but the increase of Al/V favored the V(III) in the equilibrium reaction of V(II) and V(III). [41] Czaja and Bialek reported a high activity and stability of the vanadium catalyst supported on magnesium complex with diethylaluminum chloride as cocatalyst. They attributed it to the resistance of reducing active vanadium (III) to inactive vanadium(II) by the organoaluminium co-catalyst.…”