Abstract: A process for the preparation of blends including an ethylene copolymer by copolymerizing ethylene and at least one comonomer selected from a compound represented by the formula H2C?CHR wherein R is an alkyl group or an aryl group, and a diene, in the presence of a solid catalyst system comprising a support, a transition metal compound and an activator capable of converting the transition metal compound into a catalytically active transition metal complex.

Abstract: This invention relates to olefin polymers particularly suited to satisfying the dielectric properties required in electrical device use. The olefin polymers can be prepared by contacting polymerizable olefin monomers with catalyst complexes of Group 3–11 metal cations and noncoordinating or weakly coordinating anion compounds bound directly to the surfaces of finely divided substrate particles or to polymer chains capable of effective suspension or solvation in polymerization solvents or diluents under solution polymerization conditions. Thus, the invention includes polyolefin products prepared by the invention processes, particularly ethylene-containing copolymers, having insignificant levels of mobile, negatively charged particles as detectable by Time of Flight SIMS.

Abstract: A catalyst system useful to polymerize and co-polymerize polar and non-polar olefin monomers is formed by in situ reduction with a reducing agent of a catalyst precursor comprising {Cp*MRR?n}+{A}? wherein Cp* is a cyclopentadienyl or substituted cyclopentadienyl moiety; M is an early transition metal; R is a C1–C20 hydrocarbyl; R? are independently selected from hydride, C1–C20 hydrocarbyl, SiR?3, NR?2, OR?, SR?, GeR?3, SnR?3, and C?C-containing groups (R?=C1–C10 hydrocarbyl); n is an integer selected to balance the oxidation state of M; and A is a suitable non-coordinating anionic cocatalyst or precursor. This catalyst system may form stereoregular olefin polymers including syndiotactic polymers of styrene and methylmethacrylate and isotactic copolymers of polar and nonpolar olefin monomers such as methylmethacrylate and styrene.

Abstract: In one embodiment the invention is a polymerizable composition comprising a) an organoborane amine complex; b) one or more of monomers, oligomers or polymers having olefinic unsaturation which is capable of polymerization by free radical polymerization; c) one or more compounds, oligomers or prepolymers having a siloxane backbone and reactive moieties capable of polymerization; and d) a catalyst for the polymerization of the one or more compounds, oligomers or prepolymers having a siloxane backbone and reactive moieties capable of polymerization. This composition may further comprise a compound which causes the organoborane amine complex to disassociate.

Abstract: The present invention relates to a catalyst for polymerization of a conjugated diene or the like, which is composed of a metallocene-type cation complex of a gadolinium compound. Examples of such catalyst include a metallocene-type cation complex of a trivalent gadolinium compound represented by the general formula (I): RaGdXb (wherein, Gd represents gadolinium; R represents a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group, a substituted indenyl group, a fluorenyl group, or a substituted fluorenyl group; X represents an anion; “a” represents an integer of 1 or 2; and “b” represents an integer of 1 or 2). The present invention provides a catalyst by which polymerization of a conjugated diene or copolymerization of a conjugated diene and an aromatic vinyl compound can be carried out efficiently and inexpensively.

Abstract: A transition metal complex having the following Formula (A): wherein the monovalent groups R1 and R2 are —Ra, —ORb, —NRcRd, and —NHRe; the monovalent groups Ra, Rb, Rc, Rd and Re, and the divalent group R3 are (i) aliphatic hydrocarbon, (ii) alicyclic hydrocarbon, (iii) aromatic hydrocarbon, (iv) alkyl substituted aromatic hydrocarbon (v) heterocyclic groups and (vi) heterosubstituted derivatives of said groups (i) to (v); M is a Group (3) to (11) or lanthanide metal; E is phosphorus or arsenic; X is an anionic group, L is a neutral donor group; n is (1) or (2), y and z are independently zero or integers, such that the number of X and L groups satisfy the valency and oxidation state of the metal M. n is preferably (2) and the two resulting R1 groups are preferably linked.

Abstract: A process for the trimerization of olefins is disclosed, comprising contacting a monomeric olefin or mixture of olefins under trimerization conditions with a catalyst which comprises (a) a source of chromium, molybdenum or tungsten (b) a ligand containing at least one phosphorus, arsenic or antimony atom bound to at least one hydrocarbyl or heterohydrocarbyl group having a polar substituent, but excluding the case where all such polar substituents are phosphane, arsane or stibana groups; and optionally (c) an activator.

Abstract: A catalyst system useful to polymerize and co-polymerize polar and non-polar olefin monomers is formed by in situ reduction with a reducing agent of a catalyst precursor comprising {Cp*MRR?n}+{A}? wherein Cp* is a cyclopentadienyl or substituted cyclopentadienyl moiety; M is an early transition metal; R is a C1–C20 hydrocarbyl; R? are independently selected from hydride, C1–C20 hydrocarbyl, SiR?3, NR?2, OR?, SR?, GeR?3, SnR?3, and C?C-containing groups (R?=C1–C10 hydrocarbyl); n is an integer selected to balance the oxidation state of M; and A is a suitable non-coordinating anionic cocatalyst or precursor. This catalyst system may form stereoregular olefin polymers including syndiotactic polymers of styrene and methylmethacrylate and isotactic copolymers of polar and nonpolar olefin monomers such as methylmethacrylate and styrene.

Abstract: The invention relates to a chemical compound of formula (I), wherein M1 represents an element selected from main groups II, III or IV of the periodic table of elements; x is equal to 1, 2, 3 or 4; y is equal to 2, 3 or 4, and; A represents a cation of main group V of the periodic table of elements; R1 is the same or different and represents a branched or unbranched linear or cyclic C1–C40 group that contains carbon; R2 is the same or different and represents a branched or unbranched linear or cyclic C1–C40 group that contains carbon; R3 represents a branched or unbranched linear or cyclic C1–C40 group that contains carbon, and; R4 represents a hydrogen atom; whereby R2 and R3 are always different from one another

Abstract: The present invention provides isotactic polypropylene compositions suitable for cast film applications, cast polypropylene films made therefrom, and processes for forming such films. The novel polypropylene films are formed from film resins having a melt flow ratio of from 6–15 dg/min, with a narrow molecular weight distribution, narrow composition distribution, low level of solvent extractables, and increased film clarity (i.e., decreased haze %) compared to prior art Ziegler-Natta polypropylene film resins. The polypropylene films can be cast from an extruded polypropylene polymer, the extruded isotactic polypropylene polymer being formed by polymerization with a fluorided silica supported catalyst.

Abstract: The present invention provides a non-metallocene catalyst comprising a complex having one or more ligands coordinated a transition metal. The catalyst contains substituents bonded to the transition metal through a heteroatom such as oxygen or sulfur. Furthermore, the complex includes a Group 3 to 10 transition or lanthanide metal and one or more anionic or neutral ligands in an amount that satisfies the valency of the metal such that the complex has a net zero charge. The present invention also discloses a method for preparing the catalyst and polymerizing olefins utilizing the catalyst of the present invention.

Abstract: A cocatalyst or cocatalyst component, including a compound corresponding to the formula: (A*+a)b(Z*J*j)?cd, wherein: A* is a cation of from 1 to 80 atoms, not counting hydrogen atoms, Z* is an anion group of from 1 to 50 atoms, not counting hydrogen atoms, containing two or more Lewis base sites; J* is a Lewis acid of from 1 to 80, not counting hydrogen atoms, coordinated to at least one Lewis base site, and optionally two or more such J* groups may be joined together in a moiety having multiple Lewis acidic functionality, j is from 2 to 12 and a, b, c, and d are integers from 1 to 3, with the proviso that a×b is equal to c×d, and provided further that one or more of A*, Z* or J* comprises a hydroxyl group or a polar group containing quiescent reactive functionality.

Abstract: The present invention relates to a method for preparing homo- and co-polymers having high molecular weights in high yields by polymerizing cyclic olefin compounds using a complex prepared by mixing a nickel salt compound, an organoaluminoxane compound, and at least one organic boron compound.

Abstract: The invention encompasses late transition metal catalyst systems immobilized on solid supports and their use in heterogenous polymerization processes, particularly in gas phase polymerization of olefin monomers. Preferred embodiments include a late transition metal catalyst system comprising a Group 9, 10, or 11 metal complex stabilized by a bidentate ligand structure immobilized on a solid porous metal or metalloid oxide particle support, particularly those comprising silica. The gas phase polymerization process for olefin monomers comprises contacting one or more olefins with these catalyst systems under gas phase polymerization conditions.

Abstract: The present invention relates to a catalyst system for preparing styrene polymer and a method of preparing styrene polymer using the same, more particularly to a catalyst system for preparing styrene polymer capable of preventing coagulation of polymer to the reactor by preventing gelation, offering high conversion ratio, simplifying polymer production and enabling product size control, and a method of preparing styrene polymer using the same.

Abstract: Metal complexes, catalysts derived therefrom, and polymerization processes using the same, characterized by the presence of one or more nitrogen and boron containing, anionic 5-membered cyclic ligand groups, especially 1,2-azaborolyl groups, are disclosed.

Abstract: Bimodal polyolefins having a reverse or partial reversed comonomer incorporation may be prepared in the presence of a dual catalyst on the same support wherein each catalyst has a different response to temperature, ethylene partial pressures, partial pressure of non-polymerizable hydrocarbons present in the reaction mixture and hydrogen partial pressure.

Abstract: The invention relates to a catalyst system for the selective trimerization of olefins, which system is based on a titanium complex of formula (Cp-B(R)nAr)TiR13, wherein: Cp is a cyclopentadienyl type ligand, optionally substituted, B is a bridging group, based on a single atom selected from the groups 13 to 16 inclusive of the Periodic System, Ar is a aromatic group, optionally substituted, R is, independently, hydrogen, or a hydrocarbon residue, optionally being substituted and optionally containing heteroatoms, or groups R and B are joined together to form a ring, n is an integer equal to the (valency of B minus 2), and R1 is a mono-anionic group, and further comprises an activator. The present catalyst system obviates the use of toxic chromium compounds.

Abstract: An olefin polymerization pre-catalyst, an activated catalyst and a process for preparing the catalysts are described herein. The pre-catalyst has the formula: wherein the groups M and R1–R4 are defined herein. The group R4 includes a solid-support.

Abstract: A process for polymerizing and copolymerizing cyclic olefins, such as, norbornene is disclosed. The disclosed process uses a catalyst complex that exhibit a high activity for the polymerization and co-polymerization of cyclic olefins and improved stability toward heat, oxygen and moisture.

Abstract: A method is provided for the polymerization of olefins substituted with a functional group using a transition metal catalyst that, by virtue of one or more stabilizing groups incorporated within the catalyst structure, “fixes” the stereoconfiguration of each olefinic monomer relative to the transition metal complex during each successive reaction in the polymerization process. The invention substantially reduces the likelihood of olefin rearrangement at the active site of the catalyst during polymerization. In one particular embodiment, the functional group is a polar, electron-donating group and the stabilizing group is a Lewis acid substituent; examples of polymers that can be prepared with such a system include poly(vinyl acetate), poly(vinyl alcohol), and poly(vinyl ethers). Novel complexes and catalyst systems useful in the polymerization method are also provided.

Abstract: Catalyst systems and methods for olefin polymerization are disclosed. The polymerizations are performed in the presence of a clathrochelate which comprises a transition metal ion and an encapsulating macropolycyclic ligand. At least one of the capping atoms of the macropolycyclic ligand is a Group 3–10 transition metal or a Group 13 atom. When a capping atom is a Group 3–10 transition metal, the clathrochelate can be used with an activator to polymerize olefins. When a capping atom is a Group 13 atom, the clathrachelate can be used as an activator for an olefin polumerization. Clathrochelates allow polyolefin markers to fine tune catalyst reactivity and polyolefin properties.

Abstract: Supported catalyst compositions use for use in the gas-phase polymerization of one or more ?-olefins and methods for making and using the same, the catalyst composition including A) an inert support; B) a Group 4–10 metal complex corresponding to the formula: where M is a metal from one of Groups 4 to 10 of the Periodic Table of the Elements in the +2 or +4 formal oxidation state, Cp is a ?-bonded anionic ligand group, Z is divalent moiety bound to Cp and bound to M by either covalent or coordinate/covalent bonds and contains boron or a member of Group 14 of the Periodic Table of the Elements, and also nitrogen, phosphorus, sulfur or oxygen, and X is a neutral conjugated diene ligand group having up to 60 atoms, or a dianionic derivative thereof; and C) an ionic cocatalyst capable of converting the metal complex into an active polymerization catalyst represented by the formula: [L*-H]+[(C6F5)3BC6H4—O—MORCx-1Xay]?, wherein L* is a neutral Lewis base, Mo is a metal or metalloid selected from Groups 1–14 o

Abstract: A catalyst for addition polymerization obtained by contacting (A) an organoaluminum compound, (B) a specific boron compound and (C) a solid inorganic compound, and a process for producing an addition polymer characterized by polymerizing an addition-polymerizable monomer in the presence of the catalyst.

Abstract: A new class of zwitterionic metallocycles is disclosed. A positively charged Group 4-10 transition metal is chelated to two heteroatoms and one of the heteroatoms has a substituent bearing a negative charge. We have found that substitution in this position stabilizes the zwitterion form of the metallocycle. The zwitterionic metallocycle is useful for olefin polymerizations.

Abstract: A catalyst is used which comprises a cocatalyst component wherein a non-coordinating ion-containing compound is chemically bonded to a fine particulate carrier, together with a metallocene compound and a specific hydrocarbon. There are provided an olefin polymerization catalyst which produces olefin polymers containing few solvent-soluble components without a wider molecular weight distribution, and which exhibits no significant reduction in activity even after storage, as well as olefin polymerization catalyst components and a method for their storage, and a process for production of propylene polymers using them.

Abstract: An olefin polymerization catalyst system is prepared from a catalyst of formula I or II: R1–R7 and R1–R12 in formulae I and II, respectively, are each independently —H, -halo, —NO2, —CN, —(C1–C30)hydrocarbyl, —O(C1–C30)hydrocarbyl, —N((C1–C30)hydrocarbyl)2, —Si((C1–C30)hydrocarbyl)3, —(C1–C30)heterohydrocarbyl, -aryl, or -heteroaryl, each being unsubstituted or substituted with one or more —R8 and —R12 groups, respectively. Two R1–R7 can be joined to form a cyclic group. R8 in formula I is -halo, —(C1–C30)hydrocarbyl, —O(C1–C30)hydrocarbyl, —NO2, —CN, —Si((C1–C30)hydrocarbyl)3, —N((C1–C30)hydrocarbyl)2, —(C1–C30)heterohydrocarbyl, -aryl, or -heteroaryl. T in formula I is —CR9R10— wherein R9 and R10 are defined as for R1 above. R12 is independently -halo, —NO2, —CN, —(C1–C30)hydrocarbyl, —O(C1–C30)hydrocarbyl, —N((C1–C30)hydrocarbyl)2, —Si((C1–C30)hydrocarbyl)3, —(C1–C30)heterohydrocarbyl, -aryl, or -heteroaryl. E, M, m, X, Y, and n in formulae I and II are defined herein.

Abstract: A process for polymerizing ethylene is disclosed. The ethylene is polymerized with a catalyst system which comprises an activator and an indeno[2,1-b]indolyl Group 4-6 transition metal complex having open architecture. The process gives polyethylene having a broad molecular weight distribution for improved processability.

Abstract: A dual olefin polymerization process is disclosed. The process uses a bridged indenoindolyl ligand-containing Group 4 transition metal complex and an activator. It is carried out in multiple stages or in multiple reactors. The same complex and the same activator are used in all stages or reactors. Different polyolefins are made in different stages or reactors by varying the monomer compositions, hydrogen concentrations, or both. The process of the invention produces polyolefins which have broad molecular weight distributions, composition distributions, or both.

Abstract: A catalyst system useful for polymerizing olefins is disclosed. The catalyst system includes an organometallic complex that incorporates a Group 3 to 10 transition metal and a hydroxyl-depleted calixarene ligand that is chelated to the metal. Molecular modeling studies reveal that organometallic complexes incorporating such calixarene ligands, when combined with an activator such as MAO, should actively polymerize olefins.

Abstract: A spray-dried catalyst precursor composition and method of making a spray-dried catalyst precursor composition with an inert filler, magnesium, a transition metal, solvent, and one electron donor compound. The catalyst precursor composition is substantially free of other electron donor compounds, the molar ratio of the electron donor compound to magnesium is less than or equal to 1.9, and comprises spherical or substantially spherical particles having a particle size of from about 10 to about 200 ?m. Catalysts made from the spray-dried catalyst precursors and polymerization methods using such catalysts are disclosed.

Abstract: This invention relates to the field of olefin polymerization catalyst compositions, and methods for the polymerization and copolymerization of olefins, including polymerization methods using a catalyst composition. One aspect of this invention is the formation and use of a catalyst composition comprising a stannoxy-substituted half-sandwich metallocene and an activator for olefin polymerization processes. For example, this invention encompasses the preparation of (?5-C5H5)Ti(OSnPh3)Cl2, its contact with an activator, for example, zinc-impregnated chlorided alumina, to form a catalyst composition, and the use of this catalyst composition for polymerizing olefins or acetylenes.

Abstract: The present invention relates to a method for preparing homo- and co-polymers having high molecular weights in high yields by polymerizing cyclic olefin compounds using a complex prepared by mixing a nickel salt compound, an organoaluminoxane compound, and at least one fluorine-containing compound.

Abstract: A process for polymerizing ethylene is disclosed. A magnesium chloride-alcohol is used to support an organometallic complex comprising a Group 3 to 10 transition metal and an indenoindolyl ligand. The supported organometallic complex is mixed with an activator and ethylene and the ethylene is polymerized. Use of magnesium chloride containing an alcohol as the support provides an unexpected boost in catalyst activity and improves polymer rheological properties.

Abstract: A process for polymerizing olefins is disclosed. The process uses an organometallic complex with at least one non-bridged indenoindolyl ligand bonded to M. The substituent on the indole nitrogen contains an atom selected from the group consisting of S, O, P, and N. Polyolefins from the process have unexpectedly high molecular weight compared with polyolefins made using similar supported indenoindolyl complexes.

Abstract: A catalyst for olefin polymerization, comprising: a solid catalyst component comprising [A] a solid component having substantially no hydroxyl group, [B] a compound of a transition metal selected from Groups 3-11 of the Periodic Table, and [C] a mixture of an activator compound (C-1) capable of reacting with the transition metal compound [B] to form a metal complex having catalytic activity and an organoaluminum compound (C-2); and [D] an organomagnesium compound soluble in a hydrocarbon solvent which is obtained by reacting (i) an organomagnesium compound represented by the general formula: (Mt)?(Mg)?(R1)a(R2)b wherein Mt is a metal atom belonging to Groups 1-3 of the Periodic Table, R1 and R2 are hydrocarbon groups of 2-20 carbon atoms, and ?, ?, a and b are numerals satisfying the following relationship: 0??, 0<?, 0?a, 0<b, a+b>0, and r?+2?=a+b (where r is a valence of Mt) with (ii) a compound selected from an amine, an alcohol and a siloxane.

Abstract: A catalyst composition for use in dimerizing, co-dimerizing or oligomerizing olefins comprises: at least one zero-valent nickel complex; at least one acid with formula H+X? in which X? represents an anion; and at least one ionic liquid with general formula Q+ A? in which A? is an anion identical to or different from X?. The composition can also comprise a nitrogen-containing ligand. It can be used in dimerizing, co-dimerizing, oligomerizing and in polymerizing olefins.

Abstract: The present invention relates to a multinuclear metallocene catalyst for olefin polymerization and a process for olefin polymerization using the same, in which the multinuclear metallocene catalyst for olefin polymerization comprises, as a main catalyst, a transition metal compound that contains at least two metal atoms in the groups III to X of the periodic table as central metals and a ligand having a cyclopentadienyl structure bridging between the two metal atoms, and, as a cocatalyst, an aluminoxane compound, an organoaluminum compound or a bulky compound reactive to the transition metal compound to impart a catalytic activity to the transition metal compound.

Abstract: The metallocene compound according to the invention and the olefin polymerization catalyst containing the compound are intended to produce a catalyst capable of preparing an isotactic polymer with a high polymerization activity. The metallocene compound contains a substituted cyclopentadienyl group and a (substituted) fluorenyl group and has a structure wherein these groups are bridged by a hydrocarbon group or the like. The process for preparing a metallocene compound according to the invention is intended to selectively prepare a specific metallocene compound so as not to produce an isomer, and in this process an intermediate product is synthesized by a specific method.

Abstract: A catalyst system and a process for the bulk addition polymerization or of polycyclic olefins, such as norbornene, methylnorbornene, ethylnorbornene, butylnorbornene or hexylnorbornene, 1,2,3,4,4a,5,8,8a-octahydro-1,4:5,8-dimethanonapthalene, 5,5?-(1,2-ethanediyl)bisbicyclo[2.2.1]hept-2-ene, and 1,4,4a,4b,5,8,8a,8b-octahydro-1,4:5,8-dimethanobiphenylene are disclosed. The catalyst includes an organonickel or organopalladium transition metal procatalyst and an activator compound. Polymerization can be carried out in a reaction injection molding process to yield thermoplastic and thermoset molded polymeric articles possessing high glass transition temperatures.

Abstract: New polycyclic cyclopentadiene compounds having the formula (II) wherein the various substituents and symbols R1, R2, R3, R4, R5, R6, R7, Z1 and Z2 and “n” have the meaning specified in the description. These compounds can form metallocene complexes with transition metals, which have shown unusual properties in the (co)polymerization of ethylene and alpha-olefins in general.

Abstract: A catalyst composition for preparing olefin polymers. The catalyst composition includes a metallocene compound and an activating cocatalyst. In the metallocene compound, two cyclopentadienyl groups are bridged by X (carbon, silicon, germanium or tin) in a ring structure. The bite angle ? formed by the two cyclopentadienyl rings and X is equal to or greater than 100 degrees. The obtained olefin polymer has high cycloolefin conversion and a high glass transition temperature. In addition, the catalyst composition can still maintain relatively high activity at high temperature reaction conditions.

Abstract: Zwitterionic compositions of matter comprising cations [Ct]+ and anions connected together with substantially rigid fluorinated linking groups are described. These zwitterionic compositions serve as cocatalysts. They activate olefin polymerization catalysts, and can dissolve in aliphatic solvents. Synthesis and polymerization are illustrated.

Abstract: An activator for olefin polymerization catalysts is disclosed. One aspect of the activator is that it comprises a group-13 central atom connected to at least one fluorinated aryl ring that is itself substituted with a silyl acetylenic group. Some embodiments employ a neutral activator and others employ the activator as an anion coupled with a ligand-abstracting cation. These activators are discrete molecules.

Abstract: Ethylene and optional comonomers are polymerized using a supported metallocene catalyst, an alumoxane activator, and triisobutylaluminum (TIBAL). A silica support is first pretreated with a silane compound and then with an organoboron compound. The treated silica is then combined with a Group 4 metallocene complex and an alumoxane to generate a supported, activated catalyst. While it was previously thought that the particular support treatment technique used herein provided benefits only for polymerizations catalyzed by non-metallocene single-site complexes, it has now been found that similar benefits can be realized even with conventional metallocenes if TIBAL is selected as the scavenger.

Abstract: Disclosed herein are processes for polymerizing ethylene, acyclic olefins, and/or selected cyclic olefins, and optionally selected olefinic esters or carboxylic acids, and other monomers. The polymerizations are catalyzed by selected transition metal compounds, and sometimes other co-catalysts. Since some of the polymerizations exhibit some characteristics of living polymerizations, block copolymers can be readily made. Many of the polymers produced are often novel, particularly in regard to their microstructure, which gives some of them unusual properties. Numerous novel catalysts are disclosed, as well as some novel processes for making them. The polymers made are useful as elastomers, molding resins, in adhesives, etc.

Abstract: A catalyst for addition polymerization obtained by contacting (A) an organoaluminum compound, (B) a specific boron compound and (C) a solid inorganic compound, and a process for producing an addition polymer characterized by polymerizing an addition-polymerizable monomer in the presence of the catalyst.

Abstract: A transition metal catalyst component for polymerization, composed of a metal complex comprising specific ligands and a specific substituted boron group and having a bridging group, which exhibits a very high activity for an olefin type (co)polymerization or an olefin-aromatic vinyl compound copolymerization, whereby the molecular weight of a copolymer obtainable, is high. A method for producing an olefin (co)polymer and an aromatic vinyl compound-olefin copolymer, by means thereof.

Abstract: A gas phase olefin polymerization wherein the catalyst comprises a novel Group 4 transition metal complex containing a boron or aluminum bridging group containing a nitrogen containing group, especially an amido group.

Abstract: Process for the polymerization of olefins comprising contacting olefins under polymerization conditions in the presence of a catalyst system comprising the product obtained by contacting: (A) at least one transition metal organometallic compound, pyrolidyl bis(?-cyclopentadienyl)methylzirconium being excluded, and (B) an organometallic compound obtained by contacting: (a) a Lewis base having formula (I): ?wherein Ra, Rb, Rc and Rd, equal to or different from each other, are selected from the group consisting of hydrogen, halogen, linear or branched, saturated or unsaturated, C1-C10 alkyl, C6-C20 aryl, C7-C20 arylalkyl and C7-C20 alkylaryl groups; with b) a Lewis acid of formula (II) MtR13??(II) ?wherein Mt is a metal belonging to Group 13 of the Periodic Table of the Elements; R1, equal to or different from each other, are selected from the group consisting of halogen, halogenated C6-C20 aryl and halogenated C7-C20 alkylaryl groups; and (C) optionally an alkylating agent.