Abstract: The present invention relates to an olefin polymerization obtainable by depositing on a dry inorganic oxide support at least one mononuclear chromium complex, which is representable by the general formula: ##STR1## wherein: the cyclopentadienyl ligand is substituted with 4 or 5 hydrocarbyl groups (R.sub.1 -R.sub.5) containing 1 to 3 carbon atoms, andL is one or more hydrocarbyl ligands which are sufficiently reactive to enable the complex to react with the inorganic oxide without thermal activation.The catalyst can be used without thermal activation for polymerizing olefins, particulary ethylene optionally with C.sub.3-8 alpha-olefins. It produces polyolefins having broad molecular weight distribution.

Abstract: The present invention relates to an olefin polymerization catalyst obtainable by depositing on a dry inorganic oxide support a monocuclear chromium complex to produce a catalyst precursor and thereafter by thermally activating the said catalyst precursor. The catalyst is characterized in that the mononuclear chromium complex is representable by the general formula: ##STR1## wherein: the cyclopentadienyl ligand is substituted with 4 or 5 hydrocarbon groups containing 1 to 3 carbon atoms,L is either a four or five-substituted cyclopentadienyl ligand, or (CO).sub.3 R in which R is H, methyl or ethyl.The catalyst is used for polymerizing olefins, particularly ethylene optionally with C.sub.3 -C.sub.8 alpha-olefins. It produces polyolefins having a relatively high molecular weight and a broad molecular weight distribution.

Abstract: The present invention relates to an olefin polymerization catalyst obtainable by depositing on a dry inorganic oxide support a mononuclear chromium complex which is a mixture of (A) a first mononuclear chromium complex represented by the general formula: ##STR1## wherein three of R.sub.1 to R.sub.5 are H and the other two are H, or C.sub.1 -3 hydrocarbyl group, andL is one or more hydrocarbyl ligands which are sufficiently reactive to enable the complex to react with the inorganic oxide without thermal activation, and(B) a second mononuclear chromium complex representable by the general formula ##STR2## wherein the cyclopentadienyl ligand is substituted with 4 or 5 hydrocarbyl groups (R1-R5) containing 1 to 3 carbon atoms, andL has the same definition as above, being identical or different.The catalyst can be used for polymerizing olefins, particularly ethylene optionally with C.sub.3 -8 alpha-olefins. It can be thermally activated before use in olefin polymerization.