Abstract: A process and catalyst for polymerizing olefins, especially ethylene or a mixture of ethylene with up to 40 wt % (based on total monomer) or other 1-olefinic monomer, the process comprising (a) supporting a chromium compound on a refractory oxide support material, (b) adding one or more tetravalent titanium compounds, (c) heating the product under such conditions that an active polymerization catalyst in the presence of one or more organometallic compounds wherein the metal is of groups 1A, 2A, 2B or 3A of the Periodic Table (Mendeleef), especially aluminium trialkyls. Step (d) is preferably carried out in the presence of a polyene modifier. The refractory oxide support material is preferably silica. The produced polyolefins are also claimed.

Abstract: Process for polymerizing ethylene, or mixtures thereof with up to 40 wt % of other 1-olefinic monomer comprising contacting the monomer under particle form polymerization conditions at a temperature not greater than 112.degree. C. with a catalyst prepared by heat activating chromium oxide or a compound calcinable thereto, on a refractory oxide support material and a catalyst modifier comprising an aliphatic diene and a trihydrocarbyl boron. The refractory oxide support material can be, for example silica and the heat activation is preferably carried at 400.degree. to 900.degree. C. The aliphatic diene preferably contains 1 to 10 carbon atoms and can be, for example butadiene, isoprene, 1,5-hexadiene, 1,7-octadiene or ethylidene norbornene. The trihydrocarbyl boron, for example trimethyl, triethyl or triisobutyl boron. The quantity of diene is preferably 10 to 5000 moles per gram atom of chromium and the quantity or trihydrocarbyl boron is preferably 0.1 to 20 moles per gram atom of chromium.

Abstract: Process for polymerizing ethylene or mixtures of ethylene with up to 40 weight % of other 1-olefin(s) by contacting the monomer with a catalyst (A) in the presence of a catalyst modifier (B), catalyst (A) being prepared by supporting chromium trioxide, or a chromium compound calcinable thereto, on a refractory oxide support material and heat activating, catalyst modifier (B) comprising (1) a trihydrocarbyl aluminum compound and (2) an .alpha., .omega.-aliphatic diene containing a chain of at least 6 carbon atoms. The refractory oxide is preferably silica, alumina, zirconia, thoria or silica-alumina. The trihydrocarbyl aluminum compound is suitably an alkyl, aryl or alkaryl aluminum. The .alpha.,.omega.-diene is peferably 1,5-hexadiene or 1,7-octadiene. The polymerization is preferably carried out under particle form process conditions in a fluid medium.