Abstract: Supported olefin polymerization catalyst systems can be produced using waste chromium compounds. Olefin polymers can be prepared using a catalyst system composition comprising a waste chromium compound and an alkyl aluminum compound, both supported on an inorganic oxide support, wherein at least a portion of the waste chromium compound is in a hexavalent state.

Abstract: A process for the production of EPRs comprising contacting ethylene, propylene, and optionally, a diene, under polymerization conditions, with a catalyst system comprising:(A) a catalyst precursor comprising:(i) a vanadium compound, which is the reaction product of(a) VX.sub.3 wherein each X is independently chlorine, bromine, or iodine; and(b) an electron donor, which is a liquid, organic Lewis base in which VX.sub.3 is soluble;(ii) a modifier having the formula BX.sub.3 or AlR.sub.(3-a) X.sub.

Abstract: Olefins can be polymerized in the presence of a catalyst system composition comprising chromium supported on an inorganic oxide support, a pyrrole-containing compounds, and a metal alkyl. The use of this type of polymerization process can produce an olefin comonomer in-situ, resulting in polymers having decreased density and increased branching.

Abstract: This invention relates to a two component catalyst system for the polymerization of metathesis polymerizable cycloolefins, comprising (a) a tungsten compound of the formula WOX.sub.4-x (OAr).sub.x where X is chlorine, bromine or fluorine, Ar is a hindered phenyl ring having 1-5 specified substituents and x = 1, 2 or 3; and (b) an activator compound.Among the preferred molecules or groups that are substituted on the phenyl ring of the tungsten compound are phenyl, chlorine, bromine, methoxy and isopropyl groups. Ar can also represent a multi-substituted phenyl group such as 2,4-dichloro-6-methylphenyl.

Abstract: There are disclosed a catalyst which comprises a specific transition-metal compound (A) and a specific coordination complex compound (B) instead of aluminoxane, and a process for producing a styrene polymer at a reduced cost with improved efficiency by the use of the above catalyst.The catalyst according to the present invention is inexpensive compared with the conventional catalyst containing aluminoxane as the major ingredient, and exhibits a high activity in the polymerization of a styrenic monomer into styrene polymer with a high degree of syndiotacticity as well as a high yield and conversion rate.

Abstract: The present invention relates to a novel catalyst used for homopolymerization of an olefin of 2 or more carbon atoms or for copolymerization of two or more olefins of 2 or more carbon atoms, as well as to a process for producing an olefin polymer using said catalyst. High molecular olefin polymers can be produced at a high yield, by homopolymerizing an olefin or copolymerizing olefins using a catalyst system consisting of a transition metal compound of the general formula M(R).sub.l (OR').sub.m X.sub.n-(l+m) and an aluminoxane or a catalyst system comprising a transition metal compound of the general formula M(R).sub.l (OR').sub.m X.sub.n-(l+m), an aluminoxane and an organic compound having at least 2 hydroxyl groups.

Abstract: Pure syndiotactic 1,2-polybutadiene is a thermoplastic resin which has double bonds attached in an alternating fashion to its polymeric backbone. Films, fibers and molded articles can be made utilizing syndiotactic 1,2-polybutadiene. It can also be blended into rubbers and cocured therewith. Syndiotactic 1,2-polybutadiene can be made by solution, emulsion or suspension polymerization. It typically has a melting point which is within the range of about 195.degree. C. to about 215.degree. C. However, it is often desirable for the syndiotactic 1,2-polybutadiene to have a melting point of less than about 195.degree. C. This invention discloses a process for preparing syndiotactic 1,2-polybutadiene having a melting point of less than about 195.degree. C.

Abstract: A catalyst and process for the metathesis polymerization of cyclic olefins, such as dicyclopentadiene, are disclosed. The catalyst comprises the reaction product of a transition metal halide preferably tungsten, molybdenum, or tantalum halides and a diaryl carbinol of the formula ##STR1## wherein G is independently C.sub.1-12 alkyl, C.sub.1-12 alkoxy, C.sub.1-12 alkylamino, C.sub.6-20 aryl, halide, or C.sub.1-6 haloalkyl; g is independently 0 to 4; R is independently hydrogen or G or the R's are combined as a single bond or as a bridging group X, where X is CH.sub.2, CH.sub.2 CH.sub.2, O, S, SO, SO.sub.2 or NR.sup.1, and R.sup.1 is H or C.sub.1-6 alkyl. Optional co-catalysts include borohydrides, organo tin hydrides and organo aluminum compounds. Polymerization can be carried out in a reaction injection molding process to prepare a molded article.

Abstract: A method of curing dental resin according to this invention is characterized by adding a morpholine derivative to a conventional curing process, more particularly, the dental resin is cured by polymerizing (1) a polymerizable compound having at least one ethylenically unsaturated double bond in the presence of (2) a morpholine derivative, (3) 1-cyclohexyl-5-ethylpyrimidinetrione, (4) an organometal compound and (5) an organohalogen compound, in which the self-polymerizing dental resin is polymerized or cured more rapidly than is possible with the conventional process and without detriment to its transparency, color tone stability and physical properties.

Abstract: A process for polymerizing olefins is disclosed which makes use of a catalyst comprising a cyclopentadienyl yttrium halide alkali metal electron donor complex in combination with a cocatalyst comprising an alkali or alkaline earth metal alkyl. Preferred embodiments include the use of hydrogen during the polymerization.

Abstract: Crystallizable 3,4-polyisoprene and isoprene-butadiene copolymers having high vinyl contents can be synthesized in organic solvents to quantitative yields after short polymerization times by utilizing the catalyst systems of this invention. The 3,4-polyisoprene made utilizing this catalyst system is strain crystallizable and can be employed in tire treads which provide improved traction and improved cut growth resistance. This invention specifically discloses a process for the synthesis of 3,4-polyisoprene which comprises polymerizing isoprene monomer in an organic solvent at a temperature which is within the range of about -10.degree. C. to about 100.degree. C.

Abstract: Ethylene-propylene-diene monomer terpolymers having a high degree of random polymerization are produced by employing a high activity, stereo-regular olefin polymerization catalyst comprising a titanium halide-containing procatalyst, an organoaluminum compound cocatalyst and a moderately hindered aromatic heterocyclic amine as selectivity control agent. The terpolymers are elastomeric and exhibit good processability.

Abstract: Cocatalytic composition resulting from bringing an organoaluminium halide (A) into contact with an electron-donating organic compound (ED) selected from esters, amides and ketones, the organoaluminium halide (A) possessing an atomic ratio halogen (X)/aluminium (Al) of greater than 1 and less than 1.3, the halide (A) and the compound (ED) being employed in a mole ratio halide (A)/compound (ED) of greater than 20.Catalytic systems which are usable for the polymerisation of alpha-olefins, comprising such a cocatalytic composition--and a solid based on titanium trichloride complexed with an electron-donating compound.

Abstract: This invention relates to a two component catalyst system for the polymerization of metathesis polymerizable cycloolefins, comprising(a) a pure tungsten-imido compound (procatalyst) of the formulaW(NR.sup.1)X.sub.4-x (OR.sup.2).sub.x.L.sub.ywherein x=0, 1, 2, 3 or 4; y=0 or 1; R.sup.1 and R.sup.2 are alkyl, phenyl, phenyl-substituted phenyl, phenylalkyl or halogen substituted derivatives of alkyl, phenyl, phenyl-substituted phenyl or phenylalkyl; X=Br or Cl; where alkyl has 1 to 8 carbon atoms, phenyl-substituted phenyl has 12-18 carbon atoms and phenylalkyl has 7 to 20 carbon atoms; L is a donor ligand; and(b) an activator compound selected from organometals and organometal hydrides with tri-n-butyltin hydride and tri-octyltin hydride the most preferred.

Abstract: Crystallizable 3,4-polyisoprene can be synthesized in organic solvents to quantitative yields after short polymerization times by utilizing the catalyst systems of this invention. The 3,4-polyisoprene made utilizing this catalyst system is strain crystallizable and can be employed in tire treads which provide improved traction and improved cut growth resistance. This invention specifically discloses a process for the synthesis of 3,4-polyisoprene which comprises polymerizing isoprene monomer in an organic solvent at a temperature which is within the range of about -10.degree. C. to about 100.degree. C. in the presence of a catalyst system which is comprised of (a) an organoiron compound, (b) an organoaluminum compound, (c) a chelating aromatic amine, and (d) a protonic compound; wherein the molar ratio of the chelating amine to the organoiron compound is within the range of about 0.

Abstract: Ethylene-propylene rubbery copolymers having a high degree of random polymerization are produced by employing a high activity, stereoregular polymerization catalyst comprising a titanium halide-containing procatalyst, an organoaluminum compound cocatalyst and a moderately hindered aromatic nitrogen heterocycle as selectivity control agent. The ethylene-propylene copolymer has good properties and exhibits improved processability.

Abstract: A process and a catalyst for the production of mildly elastomeric primarily isotactic polyolefins characterized by intermediate average block lengths wherein olefins are polymerized in the presence of the catalyst which comprises the reaction product of a magnesium alkoxide and a tetravalent titanium halide which takes place in the presence of an electron donor, an organoaluminum compound, and a selectivity control agent which is an effectively unhindered heterocyclic aromatic nitrogen compound.

Abstract: A process and a catalyst for the production of elastomeric primarily isotactic polyolefins characterized by short average block lengths wherein olefins are polymerized in the presence of the catalyst which comprises the reaction product of a magnesium alkoxide and a tetravalent titanium halide which takes place in the presence of an electron donor, an organoaluminum compound, and a selectivity control agent which is an effectively hindered heterocyclic aromatic nitrogen compound wherein the hinderance is provided by a chloro or a methoxy group.

Abstract: This invention relates to a two component catalyst system for polymerization of metathesis polymerizable cycloolefins, comprising(a) a tungsten compound of the formula WOCl.sub.4-x (OAr).sub.x wherein Ar represents a hindered phenyl ring having bulky alkyl, alkoxyl halogen or aryl groups in the 2,6 position, i.e., diisopropyl or phenyl group and x=1, 2 or 3; and(b) an activator compound that is triphenyl tin hydride or trialkyl tin hydride, preferably a tributyltin hydride.Among the preferred molecules or groups that are substituted on the phenyl ring of the tungsten compound include chlorine, bromine, phenyl, methoxy and isopropyl. Ar may also represent a multisubstituted phenyl group such as 2,4-dichloro-6-methyl phenyl.

Abstract: Crystallizable 3,4-polyisoprene can be synthesized in organic solvents to quantitative yields after short polymerization times by utilizing the catalyst systems of this invention. The 3,4-polyisoprene made utilizing this catalyst system is strain crystallizable and can be employed in tire treads which provide improved traction and improved cut growth resistance. This invention specifically discloses a process for the synthesis of 3,4-polyisoprene which comprises polymerizing isoprene monomer in an organic solvent at a temperature which is within the range of about -10.degree. C. to about 100.degree. C. in the presence of a catalyst system which is composed of (a) an organoiron compound, (b) an organoaluminum compound, (c) a chelating aromatic amine, and (d) a protonic compound; wherein the molar ratio of the chelating amine to the organoiron compound is within the range of about 0.

Abstract: A process for producing a polymer or copolymer of an olefin which comprises polymerizing or copolymerizing at least one olefin with or without a diolefin in the presence of a catalyst composed of (A) a magnesium-containing solid titanium catalyst component containing magnesium, titanium, a halogen and an electron donor as essential ingredients and (B) an organoaluminum compound catalyst component; characterized in that(1) said catalyst further comprises (C) an organic silicon compound catalyst component having an Si--O--C or Si--N--C bond, and(2) said electron donor in the catalyst component (A) is a cyclic mono- or poly-ester such as diethyl furane-3,4-dicarboxylate, di-n-butyl 3,4-dihydro-2H-pyrane-5,6-dicarboxylate, di-isobutyl pyrrole-2,3-dicarboxylic, di-n-butyl thiophene-2,3-dicarboxylate, n-octyl pyrrolidine-2,3-dicarboxylate, and so on.

Abstract: Isoprene-butadiene copolymers having high vinyl contents can be synthesized in organic solvents to high yields after short polymerization times by utilizing the process of this invention. The isoprene-butadiene copolymers made utilizing the process of this invention have a glass transition temperature which is within the range of about 0.degree. C. to about -60.degree. C. and can be employed in tire treads which provide improved traction and improved cut growth resistance. This invention specifically discloses a process for the synthesis of isoprene-butadiene copolymers having a high vinyl content which comprises copolymerizing isoprene monomer and butadiene monomer in an organic solvent at a temperature which is within the range of about -10.degree. C. to about 100.degree. C.

Abstract: (1) A solvent-soluble ring-opened polymer constituted of 100-50% by weight of a norbornene derivative of monomer (A) represented by the formula ##STR1## wherein, R.sub.1 and R.sub.2 are the same or different and each denote hydrogen or alkyl and m denotes an interger of 0 to 2, and 0-50% by weight of another norbornene derivative of monomer (B) capable of undergoing ring-opening copolymerization with the preceding monomer (A), the polymer having a number average molecular weight of 10,000 to 50,000, a weight average molecular weight-to-number average molecular weight ratio (Mw/Mn) of up to 3, and a glass transition temperature of at least 80.degree. C., and(2) a process for producing such ring-opened polymers as stated above.

Abstract: The invention is a polymerization catalyst system including an alumoxane and a Group IV B metallocene having a heteroatom ligand. The catalyst system can be employed to polymerize olefins to produce a high molecular weight polymer.

Abstract: Ethylene homopolymers or copolymers having a very low molecular weight are continuously prepared in a fluidized bed in the presence of high concentrations of hydrogen, while maintaining high catalyst activity, by means of a vanadium-based catalyst.

Abstract: Alternating copolymers having a high alternating degree and high isotacticity, which can be produced by copolymerizing ethylene and an aromatic vinyl monomer in the presence, as a catalyst, of a transition metal compound, aluminoxane and a specific organic compound having at least two hydroxyl groups.

Abstract: A catalyst system comprising(A) a halogen compound of trivalent titanium,(B) an organo-aluminum compound of the formula,R.sub.3-(m+n) AlY.sub.m X.sub.nwhereinY is a group having at least one of oxygen, nitrogen, sulfur and phosphorus atoms linked to the aluminum atom, R is a hydrogen atom, an alkyl having 1 to 18 carbon atoms, an alkenyl having 2 to 18 carbon atoms, a cycloalkyl having 3 to 18 carbon atoms, an aryl having 6 to 18 carbon atoms, or an aralkyl having 7 to 18 carbon atoms,X is a halogen atom, and m and n are numbers satisfying the equations, 0<m<1, 0.ltoreq.n<2, 0<m+n.ltoreq.2, and(C) an electron-donor, and a method for producing an olefin polymer which comprises polymerizing olefins using said catalyst system. According to this method, highly crystalline olefin polymers having a broad melecular weight distribution can be produced.

Abstract: Vinylene copolymers composed of recurrent structural units of formula I ##STR1## wherein Ar denotes an aromatic or heterocyclic group, R denotes an inert substituent and n stands for an integer with a value from 0-8 and processes for their preparation.

Abstract: A process for preparing molded objects wherein a liquid reaction mass comprised of a metathesis polymerizable cycloolefin, a metathesis polymerization catalyst, a catalyst activator and a reaction rate moderator are charged to a mold wherein polymerization will take place, the improvement wherein said catalyst activator comprises a dialkylzinc compound. Significantly increased gel and cure times are obtained with the dialkylzinc compounds as compared to the use of aluminum alkyl activator compounds. The gel and cure times may be further controlled by the addition of a phenolic compound to the tungsten or molybdenum compound or by the addition of a Lewis base.

Abstract: Activator compositions for redox-initiated cure of adhesive compositions of ethylenically-unsaturated monomers which comprise the condensation reaction product of an alpha-hydroxy ketone, e.g., benzoin, and a primary amine, and preferably a transition metal salt. Also two-part adhesive compositions comprising such activator compositions and a process for bonding two or more adherends with such activator compositions.

Abstract: An ethylene polymerization catalyst comprising a supported precursor of vanadium trihalide/electron donor complex and alkylaluminum or boron halides, when combined with alkylaluminum cocatalyst and alkyl halide promoter, provides enhanced polymerization and productivity plus superior polyethylene.

Abstract: A method of producing a polyolefin. An olefin is polymerized in the presence of a catalyst containing (A) a catalyst component containing magnesium, titanium, halogen and an electron donor, (B) an organoaluminum compound and (C) an external electron donor which is an ether compound (C.sup.1) of the formula [1a]: ##STR1## or formula [1b]: ##STR2## wherein R.sup.1, R.sup.2, R.sup.4 and R.sup.7 are saturated or unsaturated aliphatic hydrocarbyl group having 1 to 7 carbon atoms; R.sup.3 and R.sup.6 are a hydrogen atom or a saturated or unsaturated aliphatic hydrocarbyl group having 1 to 7 carbons and R.sup.5 is a divalent aliphatic hydrocarbyl group having 1 to 7 carbon atoms. The catalyst used in the polymerization may also contain a carboxylate, organosilicon compound and/or an azo compound.

Abstract: A vanadium-based catalyst is treated with certain oxygen-containing compounds as a means of narrowing and effectively regulating the molecular weight distribution of the polymers produced with the catalyst.

Abstract: A metathesis polymerization catalyst composition comprising a binuclear catalyst, wherein said binuclear catalyst is a mixture of at least two transition metal components, wherein a first transition metal component is a halide complex of tungsten, an oxyhalide complex of tungsten or a mixture thereof and a second transition metal component is a halide complex of a transition metal selected from the group consisting of high valent transition metals belonging to Groups IV or V of the Periodic Table, from about 1 to about 3 moles of phenolic compound per mole of tungsten component, activated by a metathesis catalyst activator and containing a rate moderator.

Abstract: Disclosed is a method of reducing the activation rate of an alkyl aluminum activator in the metathesis polymerization of polycyclic cycloolefins. Activation rate is reduced by use of a bidentate Lewis base as the reaction rate moderator.

Abstract: Disclosed is a method of delaying the metathesis polymerization of strained ring cycloolefins by addition of certain nitrogen-containing compounds including various aromatic amines or mixtures thereof.

Abstract: A process for preparing molded objects wherein a liquid reaction mass comprised of a metathesis polymerizable cycloolefin, a metathesis polymerization catalyst, a catalyst activator and a reaction rate moderator are charged to a mold wherein polymerization will take place, the improvement wherein said catalyst activator comprises a dialkylzinc compound. Significantly increased gel and cure times are obtained with the dialkylzinc compounds as compared to the use of aluminum alkyl activator compounds. The gel and cure times may be further controlled by the addition of a phenolic compound to the tungsten or molybdenum compound or by the addition of a Lewis base.

Abstract: In curing dental resins, polymerizable compounds having at least one ethylenically unsaturated double bond, such as mono- or poly-functional acrylates or methacrylates are polymerized in the presence of N-cyclohexy-5-ethylpyrimidinetrione, a specific organometallic compound typically including acetylacetone copper or lithium acetate, and an organohalogen compound. The amounts of the ethylpyrimidinetrione, organometallic and organohalogen compounds used are respectively 0.1 to 10 parts by weight, 0.001 to 0.2 parts by weight and 0.1 to 5 parts by weight with respect to the polymerization compounds.

Abstract: Solutions of VCl.sub.4 in inert organic solvent are stabilized by incorporation of decomposition retardants being halogenated organic compounds having at least two halogen atoms attached to the same carbon atom and activated by adjacent electron donor groups or carbon-carbon double bonds. One of the especially preferred stabilizers is butyl perchlorocrotonate. The solutions are useful in polymerization processes.

Abstract: A process for polymerizing or copolymerizing a member of the group consisting of an alpha olefin or mixtures thereof, consisting of the steps of:polymerizing an alpha olefin in a polymerization reactor using a polymerization catalyst, a cocatalyst, and an amount of hydrogen adjusted for molecular weight control as measured by melt flow;rapidly changing the melt flow of the polymerized alpha olefin from high to low melt flow by reacting a portion of the unreacted hydrogen in the reactor with a quantity of the alpha olefin present therein by interaction with a hydrogenation catalyst; andremoving the hydrogenation catalyst from the reactor through continuous exchange of the reactor contents.

Abstract: A process for producing a polymer or copolymer of an olefin which comprises polymerizing or copolymerizing at least one olefin with or without a diolefin in the presence of a catalyst composed of (A) a magnesium-containing solid titanium catalyst component containing magnesium, titanium, a halogen and an electron donor as essential ingredients and (B) an organoaluminum compound catalyst component; characterized in that(1) said catalyst further comprises (C) an organic silicon compound catalyst component having an Si--O--C or Si--N--C bond, and(2) said electron donor in the catalyst component (A) is a cyclic mono- or poly-ester such as diethyl cyclohexene-1,2-dicarboxylate, di-n-butyl 1,3-cyclohexadiene-1,2-dicarboxylate, diethyl furane-3,4-dicarboxylate, di-n-butyl 3,4-dihydro-2H-pyrane-5,6-dicarboxylate, diethyl ester of cyclohexene-1,6-dicarboxylic acid, and so on.

Abstract: Disclosed is a method of reducing the activation rate of an alkyl aluminum activator in the metathesis polymerization of polycyclic cycloolefins. Activation rate is reduced by use of a bidentate Lewis base as the reaction rate moderator.

Abstract: A packaging transparent propylene copolymer film stretched in at least one direction, which consists of a copolymer of propylene and an .alpha.-olefin having 4 or more carbon atoms or a copolymer of propylene, an .alpha.-olefin having 4 or more carbon atoms and ethylene. The copolymer satisfies the following conditions;(1) the content of the .alpha.-olefin having 4 or more carbon atoms in the copolymer is 8-25 mole %,(2) the content of ethylene in the copolymer is 5 mole % or less,(3) the content of a cold xylene-soluble portion in the copolymer is 15-50% by weight, and(4) the flexural modulus of the copolymer is 2,500-7,000 kg/cm.sup.2.

Abstract: Metal halide particles useful, among other things, as olefin polymerization catalyst precursors and catalyst supports, are prepared by vaporizing the metal halide and then condensing it in the presence of a diluent.

Abstract: Disclosed is a method of reducing the activation rate of an alkyl aluminum activator in the metathesis polymerization of strained ring cycloolefins. Activation rate is reduced by use of certain nucleophilic Lewis bases as the reaction rate moderator.

Abstract: A process for producing a polymer or copolymer of an olefin which comprises polymerizing or copolymerizing at least one olefin with or without a diolefin in the presence of a catalyst composed of (A) a magnesium-containing solid titanium catalyst component containing magnesium, titanium, a halogen and an electron donor as essential ingredients and (B) an organoaluminum compound catalyst component; characterized in that(1) said catalyst further comprises (C) an organic silicon compound catalyst component having an Si-O-C or Si-N-C bond, and(2) said electron donor in the catalyst component (A) is selected from the group consisting of a cyclic mono- or poly-ester such as, diethyl cyclohexene-1,2-dicarboxylate, diethyl furane-3,4-dicarboxylate, di-isobutyl pyrrole-2,3-dicarboxylate, diethyl cyclohexene-1,6-dicarboxylate, di-n-propyl 1,2-benzenediacetate, and n-butyl tetrahydrothiophene-2,3-dicarboxylate.

Abstract: A process for homopolymerizing an olefin or copolymerizing an olefin with another olefin in the presence of a catalyst composed of(a) a solid catalyst component containing magnesium atoms, titanium atoms, halogen atoms, and an electron donor compound,(b) an organoaluminum compound represented by the formula R.sup.1 R.sup.2 R.sup.3 Al (wherein R.sup.1, R.sup.2, and R.sup.3, which may be the same or different, each denote a C.sub.1-20 alkyl, alkenyl, cycloalkyl, aryl, aralkyl, or alkoxy group, or a hydrogen atom;(c) an organoaluminum compound represented by the formula R.sup.4.sub.3-n AlX.sub.n (wherein R.sup.4 denotes a C.sub.1-20 alkyl, alkenyl, cycloalkyl, aryl, aralkyl, or alkoxy group; X denotes a halogen atom; and n.gtoreq.1),(d) an electron donor compound containing a nitrogen atom, sulfur atom, oxygen atom, or phosphorus atom, and(e) an aromatic ester compound.

Abstract: Preparation of polyethylene in the presence of selected nickel-containing catalysts.

Abstract: A highly active catalyst suitable for the polymerization of olefins and its use are disclosed, said catalyst being prepared by(1) co-comminuting an aluminum halide; at least one electron donor; a Group IVB-VIB transition metal compound; and a support base selected from the group consisting of the Group IIA and IIIA salts and the salts of the multivalent metals of the first transition series with the exception of copper to produce a coground solid;(2) extracting said coground solid with an organic liquid; and(3) separating the solid from the liquid under such conditions that at least 5 weight percent of the aluminum in the coground solid is removed.

Abstract: An aromatic hydrocarbon modified soluble mixed aluminum hydrocarbyl-Lewis base co-catalyst composition comprising (i) at least two different classes of aluminum hydrocarbyls the first being an aluminum hydrocarbyl halide, the second being an aluminum hydrocarbyl hydride and/or aluminum trialkyl and (ii) at least one Lewis base represented by the formula: ##STR1## wherein each Y can be --OR', --NR.sub.2 and R' with the proviso that at least two be --OR' or --NR.sub.2, Z is an alkylene radical forming a 5 or 6 membered ring with the carbonyldioxy group or Z is alkyl substituted alkylene group wherein the alkyl radical can have from 1 to 8 carbon atoms, R is an aryl, allyl or alkyl group having from 1 to 20 carbon atoms and R' is an alkyl, cycloalkyl, aryl or aralkyl radical having from 1 to 20 carbon atoms.The co-catalyst is employed with a titanium halide catalyst for the polymerization of olefins to obtain a advantageous balance of catalytic activity and polymer product stereoregularity.