Abstract: Novel silylene or ethylene bis(tetrahydrofluorenyl)metallocenes are synthesized and used as olefin polymerization catalysts.

Abstract: The olefin polymerization catalyst comprises a supported transition metal, magnesium and halogen; the support comprises aluminum phosphate and at least one oxide of silica or alumina. The catalyst is formed by impregnating the support with a liquid complex formed by reacting a magnesium compound and a transition metal compound, which can contain either oxygen or halogen, and then precipitating the complex on the support with an organoaluminum compound which may be halogenated. The catalyst is used with an organometallic cocatalyst.

Abstract: Process for the preparation of a catalyst for the polymerization of alpha-olefins involves contacting a porous polyolefin support with a solution containing an activator (ii) to form a suspension. The suspension is evaporated in a reactor fitted with a stirrer comprising a scraping element. The scraping element follows the walls of the reactor at a distance from 2 to 200 times the mean particle diameter of the support. The catalyst includes a compound of a transition metal (i) from Groups 4 to 6 of the Periodic Table and at least one optionally substituted cyclopentadiene ligand and an aluminoxane activator (ii). The aluminoxane activator (ii) and transition metal compound are supported on the porous polyethylene support (iii). The walls of the reactor show no traces of crusting.

Abstract: Disclosed is for the preparation of a catalytic composition for the polymerization of alpha-olefins. The catalyst comprises a compound of a transition metal (i) of Groups 4 to 6 of the Periodic Table, containing at least one possibly substituted cyclopentadiene ligand, and an activator (ii) chosen from aluminoxanes and ionizing agents supported on a support (iii) consisting of porous particles of polyolefin(s). Preparation includes a preliminary polymerization which includes contact with an alpha-olefin, under polymerizing conditions, in a diluent whose kinematic viscosity, measured at 20° C., is from 3 to 3000 cSt (centistokes) from 3 to 3000 mm2/s, such as mineral oil which may be derived from coal tars and petroleum fractions, to form from 0.01 to 50 g of polyolefin per g of catalyst containing compounds (i), (ii) and (iii).

Abstract: The invention relates to a process for the production of ethylene polymers by the polymerization of ethylene or the copolymerization of ethylene with one or more C3 to C8 olefins in contact with a chromium-based catalyst deposited on a support essentially consisting of silica. According to the invention, the chromium catalyst is subjected in succession to a heat treatment in nitrogen and then to a heat treatment in air under defined temperature conditions before bringing it into contact with ethylene and, optionally, one or more olefins under polymerizing conditions. The process of the invention makes it possible to manufacture ethylene polymers having an improved compromise between processability, stiffness and resistance to slow crack growth.

Abstract: Asymmetric silicon-bridged metallocenes represented by the general formula: wherein M represents a transition metal selected from Ti, Zr and Hf. X and X′ represent a halogen atom, R1, R2, R3 represent alkyl groups containing 1 or 2 carbon atoms or hydrogen atoms, providing that at least two of R1, R2, R3 are alkyl groups, and R4 and R5 represent alkyl or aryl group containing from 1 to 10 carbon atoms. A process for their preparation and polymerization of olefins in the presence of the asymmetric silicon-bridged metallocenes are disclosed.

Abstract: Process for the preparation of a composition containing ethylene polymers comprising a polymer of melt index MI2 of 5 to 1000 g/10 min and a polymer of melt index MI5 of 0.01 to 2 g/10 min, the ratio of these indices being from 500 to 50,000 and the weight ratio of the two polymers being equal to (30 to 70):(70 to 30), according to which part of the ethylene, a catalyst derived from a transition metal having an intrinsic molecular weight distribution defined by an intrinsic Mw/Mn ratio less than or equal to 10 and a deactivation constant less than or equal to 0.5 h−1, and a cocatalyst are introduced into a first reactor, polymerization of the ethylene is carried out therein, a mixture comprising one of the polymers, the catalyst and the cocatalyst is drawn off from this reactor and the mixture and another part of the ethylene are introduced into a second reactor, which ethylene is polymerized to form the other polymer.

Abstract: Process for the emergency stopping of a polymerization reaction in the gas phase, comprising the injection of a poison of the reaction into a polymerization reactor and the evacuation of the gaseous content of the polymerization reactor via delaying means to a burner at the maximum limited feed rate, characterized in that the delaying means simultaneously serve to obtain a homogeneous distribution of the poison of the reaction inside the polymerization reactor so as to interrupt the polymerization reaction, and to regulate the flow of gasses evacuated to the burner so as not to exceed the maximum feed rate of the burner.

Abstract: Ethylene polymer having a blow-up ratio (RB) of at least 1.4, a resistance to crazing under stress (ESCR) of at least 55 h and a melt index (MI5) of at least 0.2 g/10 min. Processes for obtaining this ethylene polymer using different catalytic systems, the first based on titanium and zirconium used in a polymerization in two reactors; the second consisting of a mixture of a titanium catalyst and a titanium and zirconium catalyst, used in a polymerization in two reactors; the third based on chromium on a support comprising at least two constituents chosen from silica, alumina and aluminium phosphates, used in a polymerization in a single or in two reactors.

Abstract: Polymeric composition containing: a) 100 parts by weight of a random copolymer of propylene and ethylene containing less than 6 weight % of ethylene, b) 0.1 to 4 parts by weight of an elastomeric block copolymer having at least one polymeric block containing predominantly polymerized monovinyl aromatic compound and at least one polymeric block containing predominantly polymerized conjugated diene, and c) 12 to 20 parts by weight of an elastic metallocene polyolefin. Use of said composition for the manufacture of shaped objects and objects so obtained.

Abstract: A continuous process for obtaining propylene polymers in the presence of a catalytic system of the Ziegler-Natta type containing a catalytic solid comprising chlorine, magnesium and titanium atoms and at least one electron-donor compound, called internal donor, a cocatalyst which is an organoaluminium compound, and optionally an electron-donor compound, called external donor, comprising the following successive stages: (a) polymerization of propylene in liquid propylene to form, per g of titanium in the catalytic solid, from 11000 to 28000 g of a prepolymer chosen from among the homopolymers of propylene, and (b) gas-phase polymerization of propylene in one or more successive fluidized-bed reactors and in the presence of the prepolymer (a), of propylene, optionally in the presence of one or more other monomers chosen from among the &agr;-olefins containing from 2 to 12 carbon atoms to produce a final propylene polymer whose fraction of particles of diameter smaller than 125 &mgr;m (FP) is at most 10 wt %.

Abstract: Continuous process for manufacturing a polyolefin resin in at least two polymerization reactors connected in series, in which the polymer suspensions leaving the reactors are transferred into hydrocyclone separators in which a flow comprising diluent and polymer particles, on the one hand, and a concentrated suspension of polymer particles, on the other hand, are formed and separated. The flows comprising the polymer particles are recycled into the first polymerization reactor.

Abstract: Ethylene polymer having a blow-up ratio (RB) of at least 1.4, a resistance to crazing under stress (ESCR) of at least 55 h and a melt index (MI5) of at least 0.2 g/10 min. Processes for obtaining this ethylene polymer using different catalytic systems, the first based on titanium and zirconium used in a polymerization in two reactors; the second consisting of a mixture of a titanium catalyst and a titanium and zirconium catalyst, used in a polymerization in two reactors; the third based on chromium on a support comprising at least two constituents chosen from silica, alumina and aluminium phosphates, used in a polymerization in a single or in two reactors.

Abstract: Process for manufacturing an olefin polymer composition in at least two polymerization reactors connected in series, in which the suspension of polymer in a diluant, formed in the first reactor, is sent into a hydrocyclone seperator in which, on the one hand, a stream comprising diluant and, on the other hand, a concentrated suspension of polymer particles are formed and separated. The concentrated suspension is then introduced into the subsequent polymerization reactor.

Abstract: Process for manufacturing olefin polymers, in which some of the suspension of olefin polymer particles formed in a diluant is drawn off from the polymerization reactor and diluted by means of a liquid before being sent into a hydrocyclone separator in which, on the one hand, a concentrated suspension of polymer particles and, on the other hand, a stream essentially comprising diluant are formed and separated.

Abstract: Process for the manufacture of a composition comprising ethylene polymers, in at least two polymerization reactors connected in series, according to which, in a first reactor, from 30 to 70% by weight with respect to the total weight of the composition of an ethylene homopolymer (A) having a melt flow index MI2 of 5 to 1000 g/10 min is formed and, in a subsequent reactor, from 30 to 70% by weight with respect to the total weight of the composition of a copolymer of ethylene and of hexene (B) having a melt flow index MI5 of 0.01 to 2 g/10 min is formed. The compositions obtained by this process exhibit a good compromise between the processing properties and the mechanical properties, which renders them capable of being used in the manufacture of articles shaped by extrusion and extrusion blow-molding, such as films and pipes.

Abstract: Process for the manufacture of a composition comprising ethylene polymers, in at least two polymerization reactors connected in series, according to which, in a first reactor, from 30 to 70% by weight with respect to the total weight of the composition of an ethylene homopolymer (A) having a melt flow index MI2 of 5 to 1000 g/10 min is formed and, in a subsequent reactor, from 30 to 70% by weight with respect to the total weight of the composition of a copolymer of ethylene and of hexene (B) having a melt flow index MI5 of 0.01 to 2 g/10 min is formed. The compositions obtained by this process exhibit a good compromise between the processing properties and the mechanical properties, which renders them capable of being used in the manufacture of articles shaped by extrusion and extrusion blow-molding, such as films and pipes.

Abstract: The invention comprises a catalyst support containing an &agr;-olefin polymer which is in the form of particles of mean size from 5 to 350 &mgr;m in which the pore volume generated by the pores of radius from 1,000 to 75,000 Å is at least 0.2 cm3/g. A catalyst usable for the polymerization of &agr;-olefins, including a compound containing at least one transition metal belonging to groups IIIb, IVb, IVb and VIb of the Periodic Table, bound in or on this support, is also described.

Abstract: Process for the polymerization of olefins using a catalytic system comprising a solid precursor containing at least one neutral halogenated metallocene derived from a transition metal and at least one ionizing agent, and an organometallic compound derived from a metal chosen from groups IA, IIA, IIB, IIIA, and IVA of the Periodic Table.

Abstract: An ethylene homopolymer having a density of from about 0.956 to about 0.970 g/cm3 and a high load melt index (190° C. and 21.6 kg) of from about 7 to about 21 g/10 min. A continuous polymerization process for the production of the ethylene homopolymer, in the presence of a diluent chosen from the group consisting essentially of n-butane, n-hexane, n-heptane, isobutane, isopentane, isooctane, 2,2-dimethylpropane, cyclopentane, cyclohexane and their mixtures, wherein ethylene is brought into contact with a chromium oxide catalyst deposited on an inorganic support containing from about 0.1 to about 5 wt % chromium and activated at a temperature from about 600 to about 900° C., at a polymerization temperature from about 55 to about 150° C., the ethylene concentration in the diluent being from about 1 to about 10 mol %. A composition consisting essentially of the ethylene homopolymer, the composition having a density of from about 0.956 to about 0.