Abstract: Polyolefin rubber which is an ethylene/propylene and/or 1-butene copolymer, which has a melt index of 0.3 to 15 dg/min and a relative density of 0.860 to 0.885, comprising 74-91 mol % of units derived from ethylene and 9-26 mol % of units derived from propylene and/or from 1-butene, characterised by a crystalline melting point J of 100.degree. to 125.degree. C. The process for obtaining this rubber consists in copolymerising, at a temperature of 150.degree.-300.degree. C. and at a pressure of 400-2000 bars, a gas stream containing 15-42% by vol. of ethylene and 58-85% by vol. of propylene and/or 1-butene, in the presence of a Ziegler-type catalyst system comprising at least one compound of a transition metal of groups IVB, VB, VIB and VIII of the Periodic Classification, and at least one organoaluminium compound and, if appropriate, in the presence of at least one chain transfer agent.

Abstract: Disclosed is a catalyst system for the homopolymerization and copolymerization of alpha-olefins having 2-8 carbon atoms, said catalyst system comprising a dimeric or tetrameric cyclopentadienyl Group 6b metal compound in which the metal has an oxidation state of +2, said Group 6b metal compound being supported on an inorganic support. The catalyst system may also contain a Group 2 or Group 3 metal alkyl compound cocatalyst.

Abstract: Novel chromium-containing compounds, such as, for example, chromium pyrrolides, are prepared by forming a mixture of a chromium salt, a metal amide, and an electron pair donor solvent, such as, for example, an ether. These novel chromium-containing, or chromium pyrrolide, compounds can be used either unsupported or supported on an inorganic oxide support to trimerize and/or polymerize olefins.

Abstract: A catalyst and process for the polymerization of cyclic olefins, such as dicyclopentadiene, are disclosed. The catalyst comprises the reaction product of a transition metal halide and a 1,4-hydroquinone of the general formula: ##STR1## wherein R is independently selected from the group of hydrogen, C.sub.1-12 alkyl, C.sub.6-20 aryl, halide, and C.sub.1-6 haloalkyl. 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 process for the polymerization of olefins in the presence of hydrogen comprising contacting the olefin, a cyclopentadienyl compound and a catalyst comprising a transition metal compound at polymerization conditions.

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: The present invention relates to a process for producing a stretched molding which comprises stretching a straight chain random copolymer having:a repeating unit (A) represented by the formula:--CH.sub.2 --CH.sub.2 --and a repeating unit (B) represented by the formula: ##STR1## the proportion of said repeating unit (B) being 0.01 to 10 mol %; and an intrinsic viscosity [.eta.] as measured at 135.degree. C. in decalin of at least 5 dl/g.A stretched molding obtained by the present invention has mechanical properties equivalent or superior to those of the conventional super high molecular weight polyethylene stretched molding and is excellent in adhesive properties, dyeability, printability and so on, and thus is greatly useful as an industrial material required to have high strength and further good adhesive properties and printability.

Abstract: An improved olefin metathesis catalyst system comprises a tungsten halide having an average of no more than about one halide substituent and no more than one oxygen substituent per tungsten with the remaining tungsten valences satisfied with phenolic substituents incorporating at least one meta or para electron withdrawing group and a triorganotin hydride and, optionally, a boron halide promoter. The catalyst system forms a relatively stable polymerization mixture with polycycloolefins and effectively polymerizes dicyclopentadiene in the presence of water.

Abstract: A Grignard reagent having the formula RMgX where R is a cycloalkyl or cycloalkenyl group and X is Cl, Br or I, is used as the catalyst activator for the metathesis polymerization of dicyclopentadiene and other polycyclic cycloolefins.

Abstract: A reaction solution comprising a mixture of tricyclopentadiene, a norbornene monomer with at least 3 rings in its backbone, a 5-alkenyl-2-norbornene pot life adjusting agent along with a molybdenum type catalyst system gives prolonged pot life without extending time to exotherm (e.g., smoking time). By utilizing this reaction solution it is possible to bulk polymerize reinforced or unreinforced articles in a mold via ring-opening polymerization. Articles so obtained have good outward appearance and excellent physical properties.

Abstract: A transparent resin material consisting of a hydrogenation product of a (co)polymer obtained by subjecting at least one compound represented by general formula (I) or a combination of at least 5% by weight of said compound and 95% by weight or less of other copolymerizable cyclic olefin monomer to metathesis polymerization: ##STR1## wherein A and B are independently hydrogen atoms or C.sub.1-10 hydrocarbon groups; and X and Y are independently hydrogen atoms, C.sub.1-10 hydrocarbon groups, --C(CH.sub.2).sub.n COOR.sup.1 groups or --(CH.sub.2).sub.n OCOR.sup.1 groups [R.sup.1 is a C.sub.1-20 hydrocarbon group and n is 0 or an integer of 1-10] with the proviso that at least one of X and Y is selected from the above --(CH.sub.2).sub.n COOR.sup.1 and --(CH.sub.2).sub.n OCOR.sup.1 groups. Said transparent resin material is moldable and has sufficient optical properties, low hygroscopicity, good heat resistance and excellent adhesion to recording layer.

Abstract: An improved thermoset polymer having good mechanical properties and no detectable dicyclopentadiene odor is obtained by the ring-opening polymerization of a novel mixture of adducts comprising divinyl cyclohydrocarbon compound, such as 3,5-divinylcyclopentene and cyclopentadiene, optionally with added cycloolefinic compound, such as dicyclopentadiene, at polymerization conditions in the presence of an olefin metathesis catalyst.

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: Disclosed is a method of moderating the catalyst activation characteristics of an alkyl aluminum compound by the use of hydrocarbon substituted acetylene. Preferred compounds are phenylacetylene, hexyne-1-and hexyne-2.

Abstract: A process for producing a molded article by introducing a reactive liquid mixture which comprises a cycloalkene containing dicyclopentadiene, a norbornene-type monomer containing at least one N-substituted 5-membered cyclic imide group and a metathesis polymerization catalyst system and which has moderated metathesis polymerizability into a mold in which the liquid mixture is metathesis polymerized, and a multi-part polymerizable composition for producing the molded article.

Abstract: A transparent resin material consisting of a (co)polymer obtained by subjecting at least one compound represented by the general formula (I) or a combination of said compound and other copolymerizable monomer to metathesis polymerization, or a hydrogenation product of the (co)polymer: ##STR1## wherein A and B are independently hydrogen atoms or C.sub.1-10 hydrocarbon groups; X and Y are independently hydrogen atoms, C.sub.1-10 hydrocarbon groups, halogen atoms, halogen-substituted C.sub.1-10 hydrocarbon groups, --(CH.sub.2).sub.n COOR.sup.1, --(CH.sub.2).sub.n OCOR.sup.1, --(CH.sub.2).sub.n OR.sup.1, --(CH.sub.2).sub.n CN, --(CH.sub.2).sub.n CONR.sup.2 R.sup.3, --(CH.sub.2).sub.n COOZ, --(CH.sub.2).sub.n OCOZ, --(CH.sub.2).sub.n OZ or --(CH.sub.2).sub.n W [R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are independently C.sub.1-20 hydrocarbon groups, Z is a halogen-substituted hydrocarbon group, W is SiR.sub.p.sup.5 D.sub.3-p (R.sup.5 is a C.sub.1-10 hydrocarbon group, D is a halogen atom, --OCOR.sup.5 or --OR.sup.

Abstract: Polymer having a polymodal MWD ethylene copolymer are prepared by conducting the polymerization in a substantially mix free reactor using an essentially transfer agent free reaction mixture, the reaction being carried out in a manner such that the propagation of essentially all copolymer chains is initiated simultaneously. In carrying out the process of this invention, the catalyst components are premixed and aged prior to introduction into the reactor. The process is preferably carried out in a tubular reactor using VCl.sub.4 and aluminum sesquichloride as the catalyst system.

Abstract: Dielectric supports for electronic components, such as circuit boards, are provided which are comprised of two or more bulk polymerized norbornene-type monomers. The monomers may be easily processed into circuit boards, etc. by reaction injection molding. The copolymers obtained exhibit high heat distortion temperatures and good dielectric properties and a balance of properties that make them, for example, well suited for molded wire board materials.

Abstract: This invention is a process for preparing a polymer which comprises contacting pure dicyclopentadiene with a pure tungsten catalyst complex, such as WCl.sub.3 (2,6-diisopropylphenoxy).sub.3, when tributyl tin hydride or triphenyl tin hydride is used as the activator for the polymerization. This process affords a method of polymerization of dicyclopentadiene in which the mixture gels slowly without the use of a rate moderator at 80.degree. C. (in from about 15 seconds to as much as two minutes or more) and furthermore cures quite slowly (in about 3-6 minutes). This delay makes these compositions particularly applicable to reaction injection molding processes. Moreover, both the tungsten complexes and the tin activator compounds employed in this invention are relatively insensitive to oxygen and water.

Abstract: Process for production of a molded article comprising polymerizing a norbornene monomer having bicyclic or higher cyclic structure in the presence of a metathesis catalyst system and a viscosity modifier having room temperature viscosity of 300 to 50,000 cps which viscosity modifier comprises a ring-opened polymer and unreacted norbornene monomer having bicyclic or higher cyclic structure.

Abstract: Process for adjusting the cis-trans-double bond configuration in polyalkenamers produced by ring-opening polymerization of cis,cis-1,5-cyclooctadiene or 2-norbornene wherein the polymerization is performed in the presence of isoprene and/or a cyclic olefin with a double-bond pair in the 1,3-position.

Abstract: Methods of preparing storage stable components useful for metathesis bulk polymerization of cycloolefin monomers are provided. These components contain cycloolefins with norbornene-functional groups and cocatalysts activated with a halometal compound. In these methods, the cocatalyst is completely formed before the halometal activator is added to prevent the formation of unwanted hydrogen halides, which catalyze undesired crosslinking reactions which destabilize the cocatalyst component. Bulk polymerization systems are provided wherein these storage stable cocatalyst components are paired with catalyst components that together form the complete metathesis catalyst system. For some embodiments, storage stability is aided by the removal of water.

Abstract: Disclosed is a method of delaying the metathesis polymerization of strained ring cycloolefins by addition of certain phosphorus-containing compounds including various aryl phosphates, aliphatic phosphates, aliphatic phosphites, aryl phosphites, aryl phosphines and alkyl phosphines.

Abstract: This invention pertains to the use of organophosphonium and organoarsonium molybdates and tungstates as catalysts in a metathesis catalyst system in polymerization of cycloolefin monomers by ring opening polymerization. Polymerization can be by reaction injection molding in absence of a solvent whereby a thermoset polymer is produced or by solution polymerization in presence of a suitable solvent whereby a thermosetting or a thermoplastic polymer is produced. The cycloolefin monomers are polycycloolefins containing at least one norbornene group, and mixtures thereof.

Abstract: High vinyl polybutadiene rubber is utilized in a variety of applications. For instance, high vinyl polybutadiene is utilized in tire tread rubber compositions because it provides both good traction and rolling resistance. The present invention discloses a technique for synthesizing high vinyl polybutadiene utilizing a molybdenum catalyst system. This molybdenum catalyst system can be utilized in aliphatic solvents with high yields of about 75% being attained. The molybdenum catalyst systems of this invention are comprised of (a) a molybdenum containing compound which is prepared by modifying molybdenum pentachloride, molybdenum trichloride, or molybdenum tetrachloride with an alkyl carboxylic acid or an aryl carboxylic; and (b) an aluminum containing compound which is prepared by modifying a trialkyl aluminum compound with a phenol. The molecular weight of the high vinyl polybutadiene being prepared can be reduced by modifying the trialkyl aluminum compound with an allylphenol, such as 2-allylphenol.

Abstract: A polymer prepared by metathesis polymerizing at least one compound represented by the formula ##STR1## wherein m is 0 or 1 and R.sub.1 and R.sub.2 respectively represent hydrogen atom or an alkyl group containing up to three carbon atoms provided that both R.sub.1 and R.sub.2 are not hydrogen atom at the same time, or a mixture of said compound with at least one other metathesis polymerizable comonomer, a useful molded article, processes for preparing the polymer and a polymerizable composition therefor.

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: Process of polymerization of unsaturated hydrocarbons, with an initial induction period, by means of a catalyst constituted by a halogeno-phenate of tungsten, of which the phenate group carries one or more substituents, in the presence of an organometallic co-catalyst; the halogeno-phenate is chosen from amongst those represented by the formula ##STR1## where X is a halogen, especially Cl or Br, n is a whole number 2, 3 or 4, R.sup.1 is H or a C.sub.1 to C.sub.8 straight- or branched-chain alkoxy group, R.sup.2 is H or a C.sub.3 to C.sub.9 branched-chain alkyl group, R.sup.1 and R.sup.2 never being hydrogen simultaneously.

Abstract: A new ethylene copolymer comprising:a repeating unit (A) represented by the formula: --CH.sub.2 --CH.sub.2 --;a repeating unit (B) represented by the formula: ##STR1## (wherein R.sup.1 is defined as hereinbefore), and a repeating unit (C) represented by the formula: ##STR2## (wherein R.sup.2 and R.sup.3 are defined as hereinbefore), said repeating units (A), (B) and (C) being orientated in a random and straight chain arrangement, said repeating unit (B) content being 0 to 45 mol %, said repeating unit (C) content being 0.001 to 45 mol %, and said copolymer having a weight average molecular weight of at least 5,000.A process for producing said ethylene copolymer by using a catalyst containing a specific chromium compound.

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 modified catalyst for polymerizing alpha-olefins, for example, ethylene, is prepared by combining a chromium-compound-comprising catalyst, supported on a refractory oxide support with at least one catalyst modifier of the formula R Mg R' where R and R' are the same or different C.sub.1 -C.sub.12 hydrocarbyl, alkoxy, alkenoxy or aryloxy groups. The amount of the modifier is such that the modified catalyst composition has the molar ratio of magnesium to chromium of about 0.2 to about 1.25. The modified catalyst composition produces resins of relatively high HLMI at relatively low temperatures.There is also disclosed a process for polymerizing alpha-olefins, at relatively lower temperatures than was heretofore possible, to obtain resins of relatively high HLMI, using the modified catalyst composition. The resulting polymers can be used for the fabrication of blow-molded products, e.g., household and industrial containers.

Abstract: Disclosed is a method of making a cross-linked poly(dicyclopentadiene) with a metathesis-catalyst system, where the metathesis-catalyst system contains an organoaluminum or organoaluminum halide activator and a pentavalent tantalum catalyst. In a preferred embodiment, the cross-linked polymer is formed by combining, in a first place, a plurality of reactant streams, one reactant stream which contains the activator, a second reactant stream which contains the catalyst and at least one reactant stream which contains dicyclopentadiene; then injecting the combined reactant streams into a second place, such as a mold, where polymerization occurs. Use of the pentavalent tantalum catalyst results in the formation of a cross-linked polymer having less color and greater transparency than cross-linked poly(dicyclopentadiene) made without a pentavalent tantalum catalyst.

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: A composition and method for polymerization of cycloolefins using a feed stream including an iodide containing activator to form a substantially cross-linked polymeric product. The polymeric product may be formed by polymerization in an intricately shaped mold and/or be of ultra-low density. High glass transition temperature and fiber reinforced products are formed.

Abstract: Disclosed is a method of making a cross-linked poly(dicyclopentadiene) with a metathesis-catalyst system, where the metathesis-catalyst system contains an organoaluminum or organoaluminum halide activator and a pentavalent tantalum catalyst. In a preferred embodiment, the cross-linked polymer is formed by combining, in a first place, a plurality of reactant streams, one reactant stream which contains the activator, a second reactant stream which contains the catalyst and at least one reactant stream which contains dicyclopentadiene; then injecting the combined reactant streams into a second place, such as a mold, where polymerization occurs. Use of the pentavalent tantalum catalyst results in the formation of a cross-linked polymer having less color and greater transparency than cross-linked poly(dicyclopentadiene) made without a pentavalent tantalum catalyst.

Abstract: Thermoset polycycloolefins are obtained by polymerzing at an elevated temperature a cycloolefin containing at least one norbornene group in the presence of a metathesis catalyst system and also in the presence of an effective amount of a polyfunctional cycloolefin crosslinker containing at least one norbornene group, but preferably two or more, with two or more unsaturated sites, preferably two or more double bonds.

Abstract: A suspension which comprises an inert liquid medium, a solid material, and a transition metal compound is dried using a spray-drying technique. The spray-drying is effected under conditions of temperature and pressure which are such as to cause evaporation of the liquid medium. The solid material is preferably in a finely-divided form. The solid material may consist essentially of a transition metal compound or may be a transition metal compound which is supported on a suitable solid inert matrix material. Alternatively, a suspension of a solid support material in a solution of a transition metal compound may be used. The dried solid is obtained as an agglomerate. The agglomerated solid can be mixed with an organic compound of a non-transition metal to give an olefin polymerisation catalyst system.

Abstract: A composition for making a cellular thermoset polymer comprised of polymerized units of dicyclopentadiene monomer. The composition includes dicyclopentadiene, a catalyst, and a blowing agent.

Abstract: A composition and method for polymerization of cycloolefins using a feed stream including dialkylaluminum iodide and the cross-linked polymer produced. The polymer product may be formed by polymerization in an intricately shaped mold and/or be of ultra-low density. A trialkylaluminum compound or a dialkylaluminum chloride are preferably included with dialkylaluminum iodide.

Abstract: This invention relates to an electrically conductive p-doped poly(.beta.-diketone) and a process for forming same utilizing WCl.sub.6 as the polymerization catalyst. Doping of the resulting polymer with iodine dopant in either solution or the vapor phase or with tetracyanoquinodimethane (TCNQ) or AsF.sub.5 results in a conductive polymer having good stability in air.

Abstract: Solid polyolefin catalysts are adapted for use in low pressure gas phase fluid bed polymerization processes by being mixed with selected particulate organic support materials in a high speed bladed finishing device so as to cause the catalysts materials to become embedded in, and/or adhered to, softened particles of the support material.

Abstract: The invention is a process for polymerization of acetylene and of the derivatives thereof by a supported catalyst of the Ziegler type.This catalyst is in suspension in a liquid medium the viscosity of which is between about 10 and 400 centipoises at room temperature.The polyacetylene can be obtained in the form of film, gel, or powder that can be used for electrochemical or photovoltaic applications.

Abstract: An olefin polymerization catalyst component produced by impregnating polyethylene with a pulverized solid olefin polymerization catalyst containing a Group 4b or 5b transition metal, for example a pulverized magnesium chloride containing titanium is impregnated in low molecular weight polyethylene by copulvering, then subjecting the impregnated polymer particles to shear in an inert medium at about the softening point of the polyethylene, which when used as a cocatalyst with an organoaluminum compound produces polymers of improved morphology having a more regular shape and higher bulk density than pulverized catalyst alone.

Abstract: Disclosed is an improved method of making a cellular crosslinked polymer with a metathesis-catalyst system where a metathesis-catalyst is activated with an alkylaluminum iodide compound.In a preferred embodiment, two parts of the metathesis-catalyst system form the basis for two solutions, a catalyst/monomer solution and an alkylaluminum iodide activator/monomer solution. At least one solution also contains a blowing agent. The solutions are combined in one place, such as the mixing head of a reaction injection molding machine, and then injected into another place, such as a mold, where the monomer reacts to form a cellular crosslinked polymer.

Abstract: Incorporation of an ester plasticizer having a solubility parameter from about 7.8 to about 10.2 (cal/cc).sup.1/2 increases the flexibility and impact strength of poly(dicyclopentadiene). In a preferred embodiment of the method for poly(dicyclopentadiene) synthesis, the plasticizer is incorporated into at least one of two parts of a metathesis-catalyst system: a catalyst/monomer solution or an activator/monomer solution. The two parts are then combined in the mixing head of a reaction injection molding machine and injected into a mold where the reaction mixture rapidly sets up into a thermoset polymer with greater flexibility and impact strength than is found in the corresponding unplasticized poly(dicyclopentadiene).

Abstract: Disclosed is an improved method of making a cellular crosslinked polymer with a metathesis-catalyst system where a metathesis-catalyst is activated with an alkylaluminum iodide compound.In a preferred embodiment, two parts of the metathesis-catalyst system form the basis for two solutions, a catalyst/monomer solution and an alkylaluminum iodide activator/monomer solution. At least one solution also contains a blowing agent. The solutions are combined in one place, such as the mixing head of a reaction injection molding machine, and then injected into another place, such as a mold, where the monomer reacts to form a cellular crosslinked polymer.

Abstract: Process for preparing and treating a chromium-containing catalyst so that when the catalyst is activated the risk of explosion is substantially reduced. The catalyst comprises a complex of chromium and optionally other transition metal complexes reacted with one or more organometallic compounds of a metal of group II or III of the periodic table, which metal contains hydrocarbyl groups of 1-20 carbon atoms. The reaction product is applied to an inert inorganic support to form the catalyst component which is deactivated by treatment with oxygen or an alcohol to modify or replace residual hydrocarbyl groups. The catalyst component may be activated to form the catalyst by heating in the range 200.degree.-1200.degree. C. The catalyst is used to catalyze a polymerization of alpha-olefins.

Abstract: Incorporation of an ester plasticizer having a solubility parameter from about 7.8 to about 10.2 (cal/cc).sup.1/2 increases the flexibility and impact strength of poly(dicyclopentadiene). In a preferred embodiment of the method for poly(dicyclopentadiene) synthesis, the plasticizer is incorporated into at least one or two parts of a metathesis-catalyst system: a catalyst/monomer solution or an activator/monomer solution. The two parts are then combined in the mixing head of a reaction injection molding machine and injected into a mold where the reaction mixture rapidly sets up into a thermoset polymer with greater flexibility and impact strength than is found in the corresponding unplasticized poly(dicyclopentadiene).

Abstract: A catalyst for the ring-opening copolymerization of a hexachlorocyclopentadiene-1,5-cyclooctadiene adduct and a cycloolefin, other than cyclohexene, having 4 to 12 carbon atoms and containing at least one non-conjugated vinylene double bond. Owing to modification by oxy bidentate-type ligands, the chlorotungsten catalyst system affords a more favorable comonomer reactivity ratio and is thus utilized.

Abstract: A process is provided for transforming a polyolefin powder into a suitable substrate for the preparation of transition metal catalysts. A powder polyolefin such as polyethylene or polypropylene is treated with a solution of a magnesium alkyl. The solvent is removed by any suitable procedure such as vacuum drying. The powder is then treated with gaseous HCl or other agent suitable for decomposition of the magnesium alkyl. The powder thus prepared is an effective support for preparing high efficiency catalysts such as taught in U.S. Pat. No. 4,136,058. These catalysts give polymers of increased particle size. Polyolefin powder in the absence of such treatment is not effective as a catalyst support and will not give polymers of increased particle size.