Abstract: The present invention relates to a process for the polymerization of olefins, comprising the steps of introducing at least one olefin, at least one polymerization catalyst, at least one cocatalyst and at least one cocatalyst aid, and optionally a scavenger, into a polymerization reactor, and polymerizing the olefin, wherein the cocatalyst aid is a reaction product prepared separately prior to the introduction into the reactor by reacting at least one metal alkyl compound of group IIA or IIIA of the periodic system of elements and at least one compound (A) of the formula RmXR?n, wherein R is a branched, straight, or cyclic, substituted or unsubstituted, hydrocarbon group having 1 to 30 carbon atoms, R? is hydrogen or any functional group with at least one active hydrogen, X is at least one heteroatom selected from the group of O, N, P or S or a combination thereof, and wherein n and m are each at least 1 and are such that the formula has no net charge.

Abstract: A process for producing a Gp 2/transition metal olefin polymerisation catalyst component, in which a Gp 2 metal complex is reacted with a transition metal compound so as to produce an oil-in-oil emulsion, the disperse phase containing the preponderance of the Mg being solidified by heating to provide a catalyst component of excellent morphology. Polymerisation of olefins using a catalyst containing such a component is also disclosed. The process may be employed in the production of Ziegler-Natta catalysts.

Abstract: A method for making a solid catalytic component for a Ziegler-Natta catalyst includes contacting a particulate porous support with a solution of a hydrocarbon soluble organomagnesium precursor compound in a hydrocarbon solvent; and reacting said hydrocarbon soluble organo-magnesium precursor compound with an amount of aliphatic or aromatic alcohol, said amount being within an acceptable range of a molar equivalent of aliphatic or aromatic alcohol calculated according to formula (I): Equ Alkanol = 2 · [ ( mmole ? ? MgR / g ? ? support ) - 2.1 - 0.

Abstract: The present invention provides a method for supporting a nonmetallocene olefin polymerization catalyst, comprising the following steps: a carrier reacts with a chemical activator to obtain a modified carrier; a magnesium compound is dissolved in a tetrahydrofuran-alcohol mixed solvent to form a solution, then the modified carrier is added to the solution to perform a reaction, then filtered and washed, dried and suction dried to prepare a composite carrier; a nonmetallocene olefin polymerization catalyst is dissolved in a solvent, and then reacts with said composite carrier, then is washed and filtered, dried and suction dried, to prepare a supported nonmetallocene olefin polymerization catalyst. The present invention further relates to a supported nonmetallocene olefin polymerization catalyst as prepared by this method.

Abstract: The present invention relates to a catalyst for polymerization of ethylene, a process for preparing the same, and a method for controlling kinetic behavior of said catalyst in ethylene polymerization. Said catalyst contains a titanium-containing main catalyst component and a co-catalyst. The titanium-containing main catalyst component is prepared by reacting the following components: (1) a hydrocarbon solution of dialkylmagnesium compound of formula RMgR?.yEt3Al; (2) an alcohol compound of formula R1OH; (3) a silica support thermally activated at 200-800° C.; (4) an alkylaluminum compound of formula R2nAlCl3-n; (5) a linear halogenated alkane of formula R3X; and (6) a titanium compound of formula Ti(OR4)mCl4-m. The co-catalyst is an organoaluminum compound. Three different types of ethylene polymerization kinetic curves can be obtained by adjusting the temperature for thermally activating the silica support and the ratio of titanium to magnesium in the titanium-containing main catalyst component.

Abstract: This invention relates to an improved method for improving the tacticity of Ziegler-Natta catalyst systems and for controlling the behaviour of the active stereospecific sites.

Abstract: The invention relates to a process for preparing a catalyst support, in which zirconium dioxide powder is mixed with a binder, if desired a pore former, if desired an acid, water and, if desired, further additives to give a kneadable composition and the composition is homogenized, shaped to produce shaped bodies, dried and calcined, wherein the binder is a monomeric, oligomeric or polymeric organosilicon compound. Suitable binders are monomeric, oligomeric or polymeric silanes, alkoxysilanes, aryloxysilanes, acryloxysilanes, oximinosilanes, halosilanes, aminoxysilanes, aminosilanes, amidosilanes, silazanes or silicones. The invention also provides the catalyst support which has been prepared in this way, a catalyst comprising the support and its use as dehydrogenation catalyst.

Abstract: It has been discovered that using n-butylmethyldimethoxysilane (BMDS) as an external electron donor for succinate-containing Ziegler-Natta catalysts can provide a catalyst system that may prepare polypropylene films with improved properties. The catalyst systems of the invention provide for controlled chain defects/defect distribution and thus a regulated microtacticity along with broadened molecular weight distribution.

Abstract: Catalyst components for the polymerization of olefins comprising Mg, Ti, halogen and 1,3-diethers as internal donors having an improved balance of properties in terms of activity and morphological stability are obtained by a process comprising: (A) A first step comprising reacting an adduct of formula MgCl2(ROH)n, where R is a C1-C10 alkyl group, and n is from 0.5 to 6, with a titanium compound having at least a Ti—Cl bond at a reaction temperature ranging from 0° C. to 80° C.; (B) A subsequent step comprising contacting the solid product obtained in (A) with an electron donor ED selected from 1,3 diethers with a titanium compound having at least a Ti—Cl bond at a temperature higher than 80° C.; and (C) A subsequent step comprising reacting the solid product coming from (B) with a titanium compound having at least a Ti—Cl bond at a temperature higher than 80° C.

Abstract: This invention relates to a process for preparing magnesium alkoxide granulates. The process includes the steps of reacting magnesium metal with at least one compound of formula AlR3-nHaln and an alcohol in a non-coordinating solvent. R is an alkyl or aryl radical, Hal is a halogen radical and n is in the range of between 0 and 2.

Abstract: A polyethylene may be prepared using a mixture of a silica supported catalyst and a magnesium chloride supported catalyst. By changing the ratio of the two catalysts, the polyethylene produced may have a varying bulk density and shear response. The method allows for the tuning or targeting of properties to fit a specific application, such as a blow molding or vapor barrier film.

Abstract: For the (co) polymerization of ethylene with other 1-olefins, a Ziegler catalyst which comprises the product from the reaction of a magnesium alkoxide suspended or dispersed as ge in an inert solvent with a tetravalent transition metal compound and is subjected to a thermal after-treatment for a period of not more than 180 minutes is prepared. The catalyst gives a high yield of a polymer powder which has a broad molar mass distribution and is best suited to the production of films, hollow bodies and pipes.

Abstract: Catalyst precursors comprising Mg, Cl, Ti, and OR groups that are in molar ratios defined by the formula MgClnTip(OR)(2-n)+4p in which n is from 0.3 to less than 1.7, p is lower than 0.6, the molar ratio (OR)/Cl is lower than 4 and R is C1-C15 hydrocarbon groups. The said precursor, just upon activation with organo-Al compounds, are able to advantageously polymerize ethylene and alpha olefins, and that upon reaction with halogenating compounds generate in high yields catalyst components with high polymerization activity particularly in the polymerization of propylene also in combination with 1,3-diethers.

Abstract: A magnesium compound represented by the formula (I): Mg(OC2H5)2?n(OR1)n??(I) where R1 is CmH2m+1 (where m is an integer of from 3 to 10), and n is a numerical value satisfying 0<n<0.35; a solid catalyst component for olefin polymer using the magnesium compound; a catalyst for olefin polymer; and methods of producing olefin copolymers such as a propylene-based random copolymer and propylene-based block copolymer by using the catalyst for olefin polymer.

Abstract: A method of producing a magnesium compound by reacting the following components (i), (ii) and (iii): (i) metal magnesium (ii) an alcohol (iii) a metal dihalide compound represented by the general formula (I) containing at least 0.001 mole of M relative to one mole of magnesium of the metal magnesium (i) MX2??(I) where X is a halogen atom and M is Mn, Fe, Co or Zn.

Abstract: The present invention relates to a method for preparing a solid catalyst for ethylene polymerization and/or copolymerization. More specifically, the present invention relates to a solid titanium catalyst supported in a magnesium support which has an extremely high catalytic activity, advantageous catalyst shape and a simple preparation process, capable of producing a polymer with a high bulk density, a narrow and uniform particle size distribution and a broad molecular weight distribution, and a method for preparation of the same. A silicon-containing magnesium compound is prepared by reacting an electron donor such as a silicon compound containing an alkoxy group of Formula 1, a silicon compound containing an alkoxy group of Formula 2, or a mixture thereof in a magnesium compound solution, and reacted with a titanium compound to obtain the solid catalyst of the present invention.

Abstract: The invention refers to a process for preparing a Group 2 metal/transition metal olefin polymerisation catalyst component in particulate form having an improved high temperature activity and the use thereof in a process for polymerising olefins.

Abstract: A catalyst for olefin polymerization comprising (A) a solid catalyst component prepared by causing (a) a magnesium compound, (b) a tetravalent titanium halide compound, and (c) an electron donor compound to come in contact with each other, (B) an organoaluminum compound of the general formula R1pAlQ3-p, and (C) an oligomer of an organosilicon compound of the following chemical formula; R4—(R2R3SiO)m—R5 can produce olefin polymers having higher stereoregularity and a broader molecular weight distribution in a higher yield than conventional catalysts.

Abstract: Disclosed are catalyst systems and methods of making the catalyst systems for the polymerization of an olefin containing a solid titanium catalyst component containing an inorganic titanium compound, a magnesium alcohol adduct made from an inorganic magnesium compound and an alcohol, and a porous support having at least one of a certain specific surface area, a certain pore volume, and a certain median particle size. The catalyst system may further contain an organoaluminum compound and optionally an organosilicon compound. Also disclosed are methods of making polyolefins.

Abstract: A method for identifying a catalyst composition for use in the heterogeneous Ziegler-Natta addition polymerization of an olefin monomer, said catalyst composition comprising a procatalyst comprising a magnesium and titanium containing procatalyst and a cocatalyst said method comprising: a) providing a library comprising at least one procatalyst compound, b) forming a catalyst composition library by contacting the member of said procatalyst library with one or more cocatalysts and contacting the resulting mixture with an olefin monomer under olefin polymerization conditions thereby causing the polymerization reaction to take place, c) measuring at least one variable of interest during the polymerization, and d) selecting the catalyst composition of interest by reference to said measured variable.

Abstract: A process for the copolymerization of ethylene and ?-olefins which utilizes a mixed modifier comprised of a conjugated diene and alkoxysilane is disclosed.

Abstract: A magnesium titanium olefin polymerization procatalyst is prepared by A) reacting a diorganomagnesium compound with a source of active chlorine, (with the proviso that the amount of chlorine is insufficient to completely convert the diorganomagnesium to magnesium dichloride); then B) removing unreacted diorganomagnesium from the reaction product; then depositing a tetravalent titanium species on the reaction product. This procatalyst is highly active for the solution polymerization of olefins when combined with a cocatalyst.

Abstract: The invention refers to a process for preparing a Group 2 metal/transition metal olefin polymerization catalyst component in particulate form having an improved high temperature activity and the use thereof in a process for polymerizing olefins.

Abstract: Catalyst components, methods of forming catalyst compositions, polymerization processes utilizing the catalyst compositions and polymers formed thereby are described herein. The methods generally include providing a magnesium dialkoxide compound, contacting the magnesium dialkoxide compound with a first agent to form a solution of a reaction product “A1”, contacting the solution of reaction product “A1” with a reducing agent to form a reduced reaction product “A2”, contacting reduced reaction product “A2” with a second agent to form a solid reaction product “A3”, contacting solid reaction product “A3” with a metal halide to form reaction product “B” and contacting reaction product “B” with an organoaluminum compound to form a catalyst component.

Abstract: A process for synthesizing a catalyst component for manufacturing ethylene polymer and co-polymer. The present invention provides a process for synthesizing catalyst component (A), comprising forming a complex by contacting the solid intermediate (B) with an aluminum compound represented by formula X3-nAl(OY)n, and alkyl metal (C), wherein X is halide, Y is a hydrocarbon group or chelating carbonyl group, and wherein 1 is less than or equal to n which is less than or equal to 3, and then contacting the complex with titanium halide having formula TiX4 wherein X is halide. Solid intermediate (B) is formed by reacting magnesium metal with alkyl halide in the presence of alkoxy aluminum represented by formula Al(ORa)3, silicon halide represented by formula SiX4 and alkoxy silane represented by formula Si(ORb)4, wherein Ra and Rb are an aromatic or aliphatic alkyl group and wherein X is halide.

Abstract: The invention refers to a process for preparing a Group 2 metal/transition metal olefin polymerization catalyst component in particulate form having an improved high temperature activity and the use thereof in a process for polymerising olefins.

Abstract: The present invention relates to a process for the production of catalysts, particularly of Ziegler-Natta type of catalysts for olefin polymerisation, to the catalysts as such, and to their use in polymerising olefins.

Abstract: A process for preparing a catalyst component, comprising a Mg compound a Ti compound and an electron donor compound (ED) selected from alcohol, glycols, esters, ketones, amines, amides, nitrites, alkoxysilanes and aliphatic ethers as essential compounds, comprising two or more steps of reaction involving the use of at least one of said essential compounds as fresh reactant alone or in a mixture in which it constitutes the main component, said process being characterized by the fact that in the last of said one or more reaction steps the essential compound used as a fresh reactant is the ED compound.

Abstract: The present invention provides for a method for preparing a storable fluidic olefin polymerisation catalyst composition, said catalyst comprising an organometallic compound of a transition metal of Group 3 to 10 of the Periodic Table (IUPAC), or of an actinide or lanthanide, and the use of such composition for polymerising ?-olefins.

Abstract: A magnesium compound obtainable by reacting metal magnesium, ethanol, an alcohol having from 3 to 10 carbon atoms and a halogen and/or a halogen-containing compound containing at least 0.0001 gram atom of a halogen atom relative to one gram atom of the metal magnesium at 0 to 70° C., which comprises composition represented by the formula (I), and which has a particle diameter D50 corresponding to 50% of cumulative weight fraction of from 4 to 20 ?m and a particle size distribution index (P) of P<4.0: Mg(OC2H5)2?n(OR1)n??(I) where n is a numerical value satisfying 0<n<0.35, R1 is CmH2m+1, and m is an integer of from 3 to 10.

Abstract: The present invention relates to a preparation method of solid titanium catalyst for olefin polymerization comprising the steps of: (1) preparing a magnesium compound solution by dissolving a magnesium halide compound into a mixed solvent of a cyclic ether and one or more of alcohol; (2) preparing a carrier by adding firstly a titanium halide compound to the magnesium compound solution at low temperature, elevating the temperature of the resulted solution or aging it, and then thereto adding secondly the titanium halide compound additionally; (3) preparing a titanium catalyst by reacting the carrier with a titanium compound and an electron donor; and (4) washing the titanium catalyst with hydrocarbon solvent at high temperature.

Abstract: The present invention relates to a solid catalyst component for the polymerization of olefins CH2?CHR in which R is hydrogen or a hydrocarbon radical with 1-12 carbon atoms, comprising Mg, Ti, halogen and an electron donor selected from ?-keto-ester derivatives of a particular formula. Said catalyst components when used in the polymerization of olefins, and in particular of propylene, are capable to give polymers in high yields and with high isotactic index expressed in terms of high xylene insolubility.

Abstract: Solid fine particles which contain a magnesium atom, an aluminum atom and a C1-20 alkoxy group simultaneously, are insoluble in a hydrocarbon solvent, and have an average particle diameter of 3 to 80 ?m, and an olefin polymerization catalyst containing the solid fine particles and a transition metal compound in the groups 3 to 11 in the periodic table, exhibit a very high olefin polymerization activity without combination with an expensive organoaluminum oxy compound or organoboron compound and maintains a high activity in polymerization for a long time, and an olefin polymer excellent in powdery properties can be produced by using the olefin polymerization catalyst. The transition metal compound in the groups 3 to 11 in the periodic table includes a transition metal compound having a ligand containing two or more atoms selected from a boron atom, a nitrogen atom, an oxygen atom, a phosphorus atom and a sulfur atom.

Abstract: A solid catalyst component for olefin polymerization in which the molar ratio of residual alkoxy groups to supported titanium is 0.60 or less is obtained by reacting the following compound (a1) with the following compound (b1) at a hydroxyl group/magnesium molar ratio of 1.0 or more, reacting the reaction mixture with the following compound (c1) at a halogen/magnesium molar ratio of 0.20 or more, reacting the resultant reaction mixture with the following compounds (d1) and (e) at a temperature of 120° C. or higher but 150° C.

Abstract: A catalyst composition for the polymerization of olefins comprising the combination of one or more Ziegler-Natta procatalysts comprising one or more transition metal compounds; one or more aluminum containing cocatalysts; and a mixture comprising two or more selectivity control agents (SCA's), corresponding to the formula: (CH3O)nSi(OR)4-n, wherein R, independently each occurrence, is C2-12 alkyl, C3-12 cycloalkyl, C6-18 aryl or (poly)alkyl-substituted aryl, or C7-18 poly(aryl)-substituted alkyl, and n is an integer from zero to 4.

Abstract: A catalyst for use in the formation of polypropylene is disclosed that comprises a titanium compound having at least one titanium-halogen bond, supported on an activated, amorphous magnesium dihalide support that is essentially free of alkoxy functionality, with a titanium metal content of no more than about 2 wt %, based on the weight of the support, and an internal donor component.

Abstract: A complex compound comprising the skeletal unit (A), wherein the ring C(R1)-A1-A2-(A3)x-C(R2)—C— has delocalised unsaturation and is optionally substituted via one or more of A1, A2 and A3 by hydrogen, alkyl, aryl, halogen, or heterocyclic groups containing at least one N, S or O in a carbon ring; A1, A2 and A3 are carbon, nitrogen and, oxygen, R1 and R2 are hydrocarbyl, chlorine, bromine and iodine at least one of R1 and R2 being chlorine, bromine or iodine; x is zero or 1, 0 is oxygen, E is nitrogen, phosphorus or arsenic, Q is a divalent bridging group comprising one or more Group 14 atoms; X is a monovalent atom or group covalently or ionically bonded to M; L is a mono- or bidentate molecule datively bound to M, y satisfies the valency of M and z is from 0 to 5. The complex can be used to polymerise olefins optionally with organo-A1 or -B compounds as activator.

Abstract: The present invention relates to MgCl2.(EtOH),m(ROH)n(H2O)p adduct in which R is a C1-C15 hydrocarbon group different from ethyl, n and m are indexes, higher than 0, satisfying the equations (n+m)?0.7 and 0.05?n/(n+m)?0.95 and p is a number ranging from 0 to 0.7 with the proviso that when R is methyl and (n+m) is in the range of 0.7 to 1, the value of n/(n+m) ranges from 0.05 to 0.45. The catalyst components obtained from the adducts of the present invention are capable to give catalysts for the polymerization of olefins characterized by enhanced activity with respect to the catalysts prepared from the adducts of the prior art.

Abstract: An olefin polymerization catalyst may be prepared using a process including contacting a metal compound of the formula M(OR1)2 with a diketone to form a catalyst precursor having the general formula: wherein M is a Group IIA metal; O is oxygen; n=1 or 2; R1, R2, R3, and R4 are the same or different; and are a hydrogen or a substituted or unsubstituted alkyl or aryl moiety having from about 1 to about 20 carbons atoms.

Abstract: This invention relates to a process for the production of a polymer film or fibre wherein a polymer composition comprising a propylene homo- or copolymer is formed into a film or fibre, and wherein said propylene homo or copolymer is produced in a process which comprises the polymerization of propylene monomers or propylene monomers and one or more types of comonomers in the presence of a high yield Ziegler-Natta olefin polymerization catalyst, which catalyst comprises a component in the form of particles having a predetermined size range which has been produced in a process comprising: a) preparing a solution of a complex of a Group 2 metal and an electron donor by reacting a compound of said material with said electron donor or a precursor thereof in an organic liquid reaction medium, b) reacting said complex in solution with a compound of a transition metal to procedure an emulsion the dispersed phase of which containing more than 50 mol % of the Group 2 metal in said complex, c) maintaining the particles

Abstract: The present invention relates to a Ziegler-Natta catalyst for olefin polymerization and a method for polymerization of olefin using the same. Specifically, the invention relates to a Zeigler-Natta catalyst for olefin polymerization, which is produced by a method comprising the step of reacting a transition metal compound in which the transition metal having an oxidation number of 4 or more is selected from Groups IV, V or VI of the Periodic table and two or more aryloxy ligands are bound to the transition metal, with an organomagnesium compound, to reduce said transition metal compound to a reduced form in which the transition metal has an oxidation number of 3, and a method for polymerization of olefin using said catalyst.

Abstract: The present invention relates to a supported catalyst containing titanium, its preparation and it use in the homo-, co-, and ter-polymerization of olefin-unsaturated compounds. The present invention also relates to a catalytic system comprising a supported catalyst based on titanium and a co-catalyst selected from organo-derivatives of aluminum. More specifically, the present invention relates to catalyst supported on silica, obtained by reacting a titanium halocarboxylate and a magnesium halocarboxylate with an aluminum chloroakylderivative, in the presence of a carrier consisting of high porosity silica. The above reaction essentially takes place in the pores of the silica itself.

Abstract: A MgCl2.mEtOH.nH2O adducts, where 3.4<m?4.4, 0?n?0.7, characterized by an X-ray diffraction spectrum, taken under the condition set forth above, in which, in the range of 2? diffraction angles between 5° and 10°, at least two diffraction lines are present at diffraction angles 2? of 9.3±0.2°, and 9.9±0.2°, the most intense diffraction lines being the one at 2? of 9.3±0.2°, the intensity of the other diffraction line being less than 0.4 times the intensity of the most intense diffraction line. Catalyst components obtained from the adducts of the present invention are capable to give catalysts for the polymerization of olefins characterized by enhanced activity and/or porosity with respect to the catalysts prepared from the adducts of the prior art.

Abstract: The invention is directed to a process for producing a particulate support for an olefin polymerisation catalyst wherein a solution of a magnesium compound is contacted with a solution of an element of Group (13 or 14) of the Periodic Table (IUPAC) to obtain a solid reaction product. In the process of the invention the solid reaction product is formed by: i) contacting (a) a solution of a magnesium hydrocarbyloxy compound with (b) a solution of a halogen-containing compound of an element of Group (13 or 14) of the Periodic Table (IUPAC); and ii) recovering the solidified reaction product from the reaction mixture.

Abstract: The present invention relates to catalyst systems for polyolefin production, and more particularly, to catalyst systems for polyolefins used in producing films.

Abstract: The present invention provides a high-activity solid main catalyst component for ethylene polymerization, a process for preparing the same and a catalyst containing the same. The main catalyst component consists essentially of a magnesium compound, a titanium compound, an electron donor, an alkyl aluminum compound and fumed silica, and is prepared by a process comprising the step of: reacting powdered magnesium with an alkyl halide to form a magnesium compound in the nascent state; adding the magnesium compound in the nascent state together with a titanium compound and an alkyl aluminum compound into an electron donor to form a complex; adding and well dispersing a fumed silica thereto to form a homogeneous thick mixture; molding and drying the mixture to form main catalyst component particles with good particle morphology; and optionally, dispersing the main catalyst component particles into a hydrocarbon solvent or a mineral oil to form a slurry.

Abstract: The invention relates to supports comprising inorganic oxide particles coated with magnesium chloride and a method for making them. The inorganic oxide has a mean particle diameter of less than 5 microns and is used as a seed to crystallize magnesium chloride from solution. The magnesium chloride-coated inorganic oxide is useful for supporting transition metal compounds; the supported transition metal compounds are used as catalysts for polymerizing olefins.

Abstract: The invention relates to a method for producing a poly-1-olefin by polymerization of a 1-olefin of the formula R4C?CH2, in which R4 is hydrogen or an alkyl radical having from 1 to 10 carbon atoms, in suspension, in solution or in the gas the gas phase, at a temperature of from 20 to 200° C. and a pressure of from 0.5 to 50 bar, in the presence of a catalyst which consists of the product of the reaction of a magnesium alkoxide with a transition-metal compound (component a) and an organometallic compound (component b), whose component (a) has been produced by reacting a transitionmetal compound of titanium, zirconium, vanadium or chromium with a gelatinous dispersion of the magnesium alkoxide in an inert hydrocarbon.

Abstract: The present invention relates to silicon ether compounds having a general formula (I), a method for the preparation thereof and use thereof as a component of catalysts for polymerization of olefins. In particular, in propylene polymerization, catalyst systems comprising the silicon ether compounds as external electron donor component exhibit good hydrogen response, and can be used to prepare polymer having high isotacticity at high yield. wherein R1-R10 groups are as defined in the description.

Abstract: A process for the polymerization of olefin monomers comprising contacting ethylene or a mixture of ethylene and one or more C4-8 ? olefins with a catalyst composition comprising one or more Group 3-10 transition metal containing, Ziegler-Natta, procatalyst compounds; one or more alkylaluminum cocatalyts; and one or more polymerization control agents, said process being characterized in that at least one such polymerization control agent is an alkyl or aryl, ester of an aliphatic or aromatic (poly)carboxylic acid optionally containing one or more substituents comprising a Group 13, 14, 15, or 16 heteroatom.