Abstract: The present invention relates to a process for the start up of polymerization or copolymerization in the gas phase by bringing the said alpha-olefins in contact under polymerization or copolymerization conditions in a fluidized bed and/or with mechanical stirring with a charge powder, in the presence of a catalyst system of the Ziegler-Natta type, this process being characterized in that the charge powder used is previously dehydrated and subjected to a treatment by bringing the said charge powder into contact with an organoaluminum compound for a period of at least five minutes, so that the polymerization or copolymerization starts up immediately after the contracting of the alpha-olefins with the charge powder in the presence of the catalyst system.

Abstract: The present invention relates to a process for starting up the polymerization of ethylene or copolymerization of ethylene and at least one other alpha-olefin by bringing ethylene and optionally at least one other alpha-olefin in contact under fluidized-bed polymerization or copolymerization conditions and/or stirred mechanically, with a charge powder in the presence of a catalyst comprising a chromium oxide compound associated with a granular support and activated by thermal treatment, this catalyst being used in the form of a prepolymer, this process being characterized in that the charge powder employed is previously subjected to a treatment by contacting the said charge powder with an organo-aluminium compound, in such a way that the polymerization or copolymerization starts up immediately after the contacting of the ethylene and optionally one other alpha-olefin with the charge powder in the presence of the prepolymer.

Abstract: The present invention relates to a gas fluidized bed process for the production of copolymers having a density between 0.900 and 0.935, which process comprises copolymerization of (a) ethylene, (b) propylene and/or 1-butene, and (c) alpha-olefins comprising from 5 to 8 carbon atoms in the gaseous state, in admixture with an inert gas and optionally with hydrogen, in the presence of a catalytic system comprising a cocatalyst consisting of at least 1 organo-metallic compound of a metal of groups II and III of the Periodic Table of Elements and a special solid catalyst.

Abstract: The present invention relates to a process for the polymerization of alpha-olefins in the gas phase in the presence of a Ziegler-Natta catalyst system consisting of a catalyst comprising atoms of halogen, magnesium and a transition metal, and cocatalysts based on an organometallic compound of a metal of Groups II or III of the Periodic Table of Elements, this catalyst system being previously converted into a prepolymer or a catalyst supported on a granular substance. This process is characterized in that the polymerization in the gas phase is carried out by contacting one or more alpha-olefins, on the one hand with the prepolymer or the supported catalyst system comprising an organometallic compound (a) which is only slightly volatile as cocatalyst, and on the other hand another cocatalyst consisting of an organometallic compound (b) which is relatively volatile, in such a way that the total quantity of cocatalyst employed is relatively small.

Abstract: The invention is addressed to solid catalysts comprising essentially compounds of magnesium and of transition metals selected from the sub-groups IVa, Va and VIa of the periodic table, applicable to the polymerization of olefins and particularly ethylene, in which the catalyst is obtained by first preparing a solid compound of magnesium, monohalogenated hydrocarbon and halogen and/or organic derivatives of the transition metal in a state of valency of at least 4 and then reacting the solid compound of magnesium and transition metal with an oxidizing compound.

Abstract: This invention is addressed to catalysts for use in the polymerization of olefins comprising compounds of magnesium and one or more transition metals of groups IVa, Va and VIa, which are at least partially reduced, with the catalysts being prepared by reaction of magnesium, at least one mono-halogenated hydrocarbon and a compound of a transition metal having a valence of at least 4. The catalysts can be used for the polymerization of olefins, such as ethylene, in the low-pressure process.