Tetraalkylchromium compounds and use as olefin polymerization catalysts
United States Patent Kruse Apr. 1, 1975 TETRAALKYLCHROMIUM COMPOUNDS AND USE AS OLEFIN POLYMERIZATION [56] References Cited CATALYSTS UNITED STATES PATENTS 1 Invenwri Walter Kruse, Wilmington, 3,709,853 1/1973 Karapinka zoo/94.9 DA [73] A ig Hercules Incorporated, Wilmington 3,757,002 9/1973 Karol 260/949 DA DeL Primary ExaminefEdward J. Smith [22] Filed May 1973 Attorney, Agent, or Firm-Edith A. Rice; Edwin H. 21 App]. No.: 362,028 Dafter, r-  
  Related US. Application Data 1 v [60] Division of Ser. No. 269,693, July 7, 1972, Pat. No. [57] ABSTRACT 3,798,250, which is a continuation-in-part of Ser. No. A new class of organochromium compounds are de- 1 121018 2, 1971 abandonedscribed, namely, tetravalent chromium compounds having the formula Y Cr where Y is alkyl, cyclohexyl- Forelgll Appllcatlon &#39;y Data substituted alkyl or phenyl-substituted alkyl. Typical Dec. 30, 1971 Canada 131388 compounds are tetra(neopentyl)chromium, tetra(cyclohexylmethybchromium and tetra(neophyl)- [52] US. Cl 260/93.7, 252/430, 252/431 R, chromium. These compounds are new catalysts for the 260/949 B, 260/949 DA polymerization of l-olefins and can be used in solution [51] Int. Cl. C08f 1/30 or extended on a solid support such as silica. [58] Field of Search... 252/431 R; 260/931, 94.9 B,  
 13 Claims, No Drawings TETRAALKYLCHROMIUM COMPOUNDS AND USE AS ()LEFIN POLYMERIZATION CATALYSTS This application is a division of my copending U.S. application Ser. No. 269,693, filed July 7, 1972, now U.S. Pat. No. 3,798,250 which is in turn a continuationin-part of applications Ser. No. 1 12,018, filed February 2, 1971, and now abandoned.  
  This invention relates to new organochromium compounds and more particularly to tetraalkylchromium compounds and to their use as catalysts for the polymerization of l olefins.  
  Many complex organochromium compounds are known such as the metal carbonyls or the so-called sandwich compounds in which the organo groups are bound to the metal as planar systems as, for example. the Tr-allkyl compounds, the bis(arene) compounds and compounds such as chromocene. Alkylchromium compounds are likewise known wherein the alkyl group is a simple alkyl such as ethyl, propyl. butyl, etc., but in all such previously known alkyl compounds the chromium was divalent or trivalent and all of these compounds are very unstable, decomposing at temperatures of C. or lower when stabilizing ligands are removed.  
  Now in accordance with this invention, tetraalkylchromium compounds have been prepared, which compounds are surprisingly stable, many of them being stable at room temperature. In addition, they are excellent catalysts for the polymerization of l-olefins, being useful as catalysts under a wide variety of polymerization conditions. The tetraalkylchromium compounds of this invention have the general formula where R and R are each selected from H and methyl, and R is selected from H, alkyl, cyclohexyl, alkylcyclohexyl, cyclohexylalkyl and dimethylbcnzyl. Exemplary of these tetraalkylchromium compounds are those having the formula CrY where Y is an alkyl radical containing 1 to 8 carbon atoms such as methyl, ethyl. propyl, isopropyl, butyl, isobutyl, see-butyl, tertbutyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl, neohexyl, 2-ethylbutyl, octyl, 2-ethylhexyl, 2,2- diethylbutyl, 2-isopropyl-3-methylbutyl, etc., eyelohexylalkyls such as (CH ),,-C H where n is 1 to 4 as, for example, cyclohexylmethyl, 2-cyclohexylethyl, 3-cyclohexylpropyl, 4-cyclohexylbutyl, and the corresponding alkyl-substituted cyelohexyl radicals as, for example, (4-methylcyelohexy)methyl, and neophyl,  
 &#39;i.e., beta, beta-dimethyl-phenethyl.  
 of the alkyllithium is not highly branched. However, if 6 the alkyl group is highly branched, it is not essential that a tetravalent chromium compound be employed. By highly branched&#34; is meant that the alkyl group is branched at either or both of the carbon atoms alpha and beta to the lithium atom. In such case, any anhydrous divalent or trivalent chromium salt may be used as, for example, chromous and chromic halides, the tetrahydrofuranates of chromous and chromic chlorides, chromium acetylaeetonate and the like. For example, when neopentyllithium is reacted with chromous or chromic chloride the product is tetraneopentylchromium, tetravalent chromium being generated by a disproportionation reaction with the formation as byproducts of lower valence chromium compounds or chromium metal.  
  As already indicated the reaction between the alkyllithium and the chromium salt can be carried out in an inert aliphatic hydrocarbon diluent or in anhydrous ethyl ether. Typical hydrocarbon solvents are pentane, hexane, heptane, and octane. In general, the reaction is carried out at a low temperature such as 78C. but any temperature from about l0OC. to about C. can be used. Some of the tetraalkylchromium compounds are so thermally stable that they can be isolated by evaporation of the diluent and then purified by sublimation if desired. Others being less thermally stable are best handled in solution and stored at low temperature. These new tetraalkylchromiums are stable in anhydrous polar solvents but hydrolyze over a period of a few minutes in a water-miscible solvent such as acetone which contains water. They all react rapidly with oxygen, halogens, and acids.  
  The following examples will illustrate the preparation of the new tetraalkylchromium compounds of this invention. All parts and percentages are by weight unless otherwise stated.  
 EXAMPLE 1 Neopentylithium was prepared by reacting neopentyl chloride with lithium wire in pentane in a 1:2 molar ratio, stirring the mixture for 6 hours at 7080C.  
  To a suspension of 1.875 g. of chromic chloride tetrahydrofuranate (CrCl 3THF) in 32 g. of pentane at 78C. and under vacuum was added slowly ml. of a 0.5 M solution of neopentyllithium in pentane. The purple solution was allowed to warm to room temperature during 1 hour. Gaseous carbon dioxide was then passed in to precipitate the excess alkyllithium. After eentrifugation. the supernatant liquid was separated and evaporated to dryness under vacuum. The dark red solid that remained was transferred under argon to sublimer. lt sublimed under high vacuum at C. The yield of tetrakis(neopentyl)chromium so obtained amounted to 25% based on the CrCl 3THF used. It had a melting point of about 1 10C. and starts decomposing at about C. In hcptane solution, it decomposes at temperatures above 150C. in about 3 hours. On analysis, it was found to contain 15.287: chromium (theory is 15.48 percent). It showed a major mass spectral peak at 336 (theory 336). Electron spin resonance and magnetic susceptibility measurements showed that the chromium-had a valence of four.  
 EXAMPLE 2 Example 1 was repeated except that tert.- butyllithium was used in place of the neopentyllithium used in that example. The tetrakis(tert.- butyl)ehromium so obtained was wine red and sublimed at 55C. under high vacuum. The yield was 10 percent. Analysis for chromium showed it to contain l8.53 percent (theory is l8.5471 Electron spin resonance and magnetic susceptibility showed that the chromium was tetravalent.  
 EXAMPLE 3 EXAMPLE 4 To a solution of 450 mg. of Cr(O -tert.-butyl) in 5 ml. of pentane under vacuum at 78Cv was added slowly 8 ml. of a 0.5 M solution of neopentyllithium in pentane. A violent precipitate appeared which dissolved when the reaction mixture was allowed to warm to room temperature. Gaseous carbon dioxide was then 7 passed in to the purple solution to precipitate the ex- EXAMPLES 61 7 In each of these examples, a solution of the alkyllithium compound was added to a suspension of the chromium salt or alkoxidc in the diluent at 78C. and under vacuum. The reaction mixtures were then allowed to warm to room temperature. In each case reaction either occurred immediately or during the warming to room temperature. In Examples 7, 8 and It) to 16, the excess alkyllithium was precipitated by addition of carbon dioxide. The supernatant solution of alkylchromium compound produced in each case had the characteristic red solor (absorption peak in the visible region at about A 490 mu) that is exhibited by tetraalkylchromium compounds. That the chromium was tetravalent was further established by electron spin measurements on some of these solutions.  
  Tab&#39;ulated in Table l is the alkyllithium and chromium compound reacted and the amount thereof, the diluent used, and the midfield and lowfield signal in gauss of the electron spin resonance spectrum.  
 &#39;lablql Reactants i Product Chromlum Llthium ESR S1gnaI Example Compound g Alkyl g; E :l. 1uent m1. Midfield Lowfield Structure 6 Cr(-t:-C ll9) 0. 344 methyl 0.088 pez&#39;ltane 10 Cr(CH 4 7 0. 344 propyl 0.200 10 CI(C H 4 8 0.172 iscpropyl 0.100 Cr[Cll(CH 1 9 0. 172 n-butyl 0.128 5 3266 1520 Cr(nC lI 4 9H3 0.172 sec.-buty1 0.128 5 Cr -CI1-C H 11 CrCl 3m? 1. 875 isobutyil. 1.2a 5o Cr [CH -CH(CH 1 4 12 Cr(0-t-C H 0.172 neohexyl 0.184 10 3279 1621 Cr I-(CH -CH(CH 13 CrC1 &#39;3THF 1.875 Z-ethylbutyl 1.84 so Cr[-Cll -Cil(C !l 14 o. 375 2,2-diethy1- o. 480 10 3270 1535 c: [&#39;Cl| -C(C !l 1 4 I butyl 15 0. 375 2-isopropyl- 0.480 10 Cr -ClI -CH-C!t(Cl-I 3-methy1buty1 CH(CH 16 1.875 neophyl 11.28 diethyl 100 3250 1590 CrI-CH -c(cii -c H 1 other 2 3 2 6 5 4 17 C:(Ot-C H 4 0.344 cyggfisfiyl- 0.416 pcntane 10 3285 1571 Cr(-CH .-C H 4 cess alkyllithium. The tetrakis(neopentyl)chromium was then isolated described in Example I. The yield was 75 percent based on the chromium tetra(tert.- butylate) used. Electron spin resonance and magnetic susceptibility measurements showed that the chromium was tctravalent.  
 EXAMPLE 5 Lil  The tetraalkylchromium compounds of this invention comprise an unusual group of catalysts for the polymerization of l-olefins. They are a very versatile group of catalysts, being effective under a wide range of conditions. Any l-olefin can be polymerized by means of these new catalysts as, for example, ethylene, propylene, butene-l, hexene-l, octene-l, etc. and mixtures of these olefins.  
  These new polymerization catalysts can be used in batch or continuous processes. Generally the polymerization process is carried out in the presence of a liquid diluent such as a liquid hydrocarbon, which can be any aliphatic, cycloaliphatic or aromatic hydrocarbon that is free of ethylenic unsaturation. Exemplary of such diluents are pentane, hexane, heptane, isooetane, decane, cyclohexane, benzene, toluene, xylene, etc. A mixture of the olefin being polymerized and the liquid hydrocarbon can be allowed to flow over a fixed catalyst bed or the olefin can be passed into a mixture of the catalyst at a temperature below&#39; &#39;thatat which the polymer&#39;di&#39;ssolves or as a solution processby operating at a temperature above that at which the polymer dissolves. These catalysts can falso be ex t-ended on a solidsupport &#34;and aiily t tss wahauwti&#39;iiae eih a fli-iidized&#39;bedpioi&#39;c The tetraalk&#39;yleh r&#39;o mium *e&#39;oiiip0tintls of t&#39;his&#39;invention cahbe estehtled h ny oxldle earrieY-matetlm aster example, sliitaamn ha &#39;thofiay tltaha, &#39;et p t ted-ate hia&#39;te&#39;r&#39;m as wll a e inixedala&#39;iiil&#39;rio.  
 etc. The c&#39;i&#39;ai &#39;titir&#39;&#39; eafl he ampteghatati-ahd -ht reacted with the tetraalkylehr&#39;tshiiuhi eompohhdlh&#39;a variety of ways. A hydrocarbon solution of the tettaalltylchromium can be mixedwith oxidic material and allowed to stand until the reaction is complete or the solvent daii&#39;lje r motes tfnder &#39;viicuufn wheteupoi&#39;i the layer tat&#39;tettaallyltshrehthrht&#39;atl &#39;theksutl aee teacts altiiost immediately the t e ehto iiun is ilistvlubi&#39;libfeci ah the surfaee&#39;f thefhgl&#39;th&#39;dtartrah sbltitioricail&#39;ici m&#39;ixtute can also be ek tisea t liglitwherettphhthe-tehaallyiclilon&#39;lium is trar&#39;isft&#39;ii lned into spetaits which is hhte more reactive toward the carrier surfl i&#39;cePThi&#39;s photodeposition mustbe cagefqlly controlled to avoid 25 vators anasewW is&#39;rHleam/ar timavttil&#39;eeligh&#39;e edi be used as theseat/ astersaitstatmayl catl eated-as the activator Q?akhfiasiaarah-af thetwa eah lse used.  
 t Ememplaiy :tsfvhe-aetivators&#39; t-h&#39;at cart 58 used are hie r- &#39;drdcarl gons, oirganoalmiaimhmetimpotilids, and leadfi&#39;tin pompou&#39;mlt having the formula; l /[Bill I Where 4% as Hg;  
 &#39;Z-n, By A], 5%; hr Ge;- R tis li hydroeanbon radicai &#39;fre&#39;e of ethylenic unsaturation and-iiis the valdrweofMman be used. Examples of these compounds are those where the R&#39;s are alike or different and can be alkyl, cyclqalr kyLalkylcycloalleyl, aryl, aralkyl and alkaryl suchfas methyl, ethyl, propyl, n-butyl, tert-butyl, cyg lohexyl, phefiyl, benLyl, mlyl, etc. In addition, .compounds having the formula &#34;R-mbm. i.  
 where R is an aiiltyl; alkenyl, &#39;c jf dliialkyl, arylf,aialkyl,  
 alkartyl etc. group and X and Y are R(which can be the same or different), halide, H, alkoxide, etc. can be used. Of particular importance are the alkylaluminum dihalides or trialkylaluminum compounds. Exemplary of the organoaluminum compounds that can be used are trimethylaluminum, triethylaluminum, tri(nbutyl)aluminum, tri-isobutylaluminum, ethylaluminum dichloride, methylaluminum &#39;s&#39;esquichloride, cthylaluminum sesquichloride, diisobutylaluminum hydride, trihexylaluminum, trioctylaluminum, tridodecylalumi- 5 num, aluminum isoprenyl, triphenylaluminum, tribenzylallu&#39;m&#39;iiiilm, .tni( Gyclohexyl-)atlum in um, etc. Another type&#39;of organoaluminum eompound that can be used to activate the polymerization&#39;is&#39; the reaction product of a tnialkylalun&#39;linum withzfromziabout 0.05 toabou&#39;t. L5  
 0 nttiles&#39;iofwatewwhioh teaotioit r&#39;naly lac-carried out in situ :or the lreaction can .bescar&#39;ried&#39; out prior to the polymeaiizationlpmpess. ,When anidrgarib&#39;metallie activator is &#39;iused zit gene r&#39;ziliy&#39;will berpsed&#39; imam/amount .such&#39; that wlllllfi&#39;ililOlil&#39;f ra&#39;tio of; it.to thefchi1omium compound will-be the ratio &#34;of from about 0.5:] to 10021 and prefstably? fromtabout .ltlhtotaboutltls l.  
  the iiempenatune.atlwhidh&#39;tthe. polymeiimtion iscartiedduf&#39;will depefidiupohtthedypeofipkociessused, but zgenerally.wiill bewithin Ll-IQJ&#39;IZHIigEOF from about 0C. to about H9203 t :z&#39;tlthouglm bigl&#39;lerwor .lower temperatures mtntbe-tttsedi &#34;Anyrpre&#39;ssurej from subatmospherio to as high &#39;as fiiiuatrnosphetes or more; can be used. An&#39;y &#39;umoun&#39;tizofltheiehnomiunt compound .danbeused to eatalyze the polymerization&#39;nfrom a&#39;ihinon-catalyti amount to a large excess, if desired,  
 The following exanipleswi&#39;ll illustrate the process of polymeiiizing. rjl -tqilefi-ns .;with ether: \t&#39;etnaaIkylchromium t&#39;rdfialysgsof this-invention w t t t I t ii&#39;xawt is A polymerihation vessel of-a m ml. capacity equi ped iditlt&#39; aniagnetiostirring Bar&#39;aiid filled with argon was ehaegedrgw ith 5U ml; df h hepiahe; which had be&#39;ntreed e5 &#39;ofimptrritie&#39;s. The vessel waspalnted Black in order to exitludellght. The follewing reagemswere added hi or den; 210x moles ofttiethy-laluminum LOXIO moles oftetrattertwhmyl&#39;)&#39;ehfioniium and ethylehe to a measure of *plsitgrlher; mixture was &#34;stirred for 17 hours at 25C. dhd&#39; theii vdntedt Th&#39;- polyethylene so produced was separated and&#39;air-dried. lt amounted to 0.71 g. which was eqiiiv ale&#39;rit to 7i g. per millimole of bhroriiit&#39;tmr 1 wt t The piiooedure.&#34; described in Example l8 was re= pated-exoeptz that&#39;ari unpainted tglass&#39; vessel was used andafiter all: ing&#39;redientshad been charged, tli&#39; vessel was exposed: to afifl&#34; wattsunla&#39;iiip placed 12 inches from the bottle. The reaction was continued until the lution was colorless; 162 minutes. The polyethylene sosptoduced amountedto. l .250 vg. or g. permillimole of chromium produced at a rate of 23 g./rnmole 5 rlatralhi.  
 EXAMPLE 2O Alsamplef fill ii ii&#39;crosphqrloi&#39;dal silica gel was annealed at;- 7}ll)()C. Agzgfi ge portion of=this silica was placed in &#39;fitq lymer&#39;ii atioi ii&#39;lfessel (with a magnetic stirring bar), and the vessel was sealed and flushed with argont The ves l was c&#39;hatged with 50 mi. of n-heptane aha was placed in a bath at 50C.; ethylene was introduced to I 3?)&#34; p.s.i.g. and 5.0Xl0 moles of tetra(tert.-butyl) were added. The vessel contents were stii red for l7 hours with a constant feed of ethylene. At  
  the end of this time the vessel was vented, opened to the atmosphere, and sealed. The white solid polyethyland a rate of l6.O g./mm ole Cr/atmJhr.  
  movd with a stream of argon at50C. to deposit the chromium compound on the alumina- (0.32% Cr-b y analysis). A 1.57 g. portion of this catalyst was placed under argon in a polymerization vesselalong with300 ml. heptane. The vessel and contentswereequilibrated at 50G-..and:etl1ylene was added td37 .p.s.i. g Polymerization began on introduction of triethylaluniinum, a total of laOXlO moles of the latter being added intwo increments. ln.24;9 &#34;hours the polymerization produced 44.0 g. of polyethylene from 9.7Xll- &#34;i110l&#39;6S of chromium, a productivity of455 g. permillimole Cr and a rate of-9.l g;/mmole&#39; Cr/atm./hr.  
  EXAM PLE &#39;22 i A glass polymerization vessel equipped with. a magnetic stirring bar and filled with argon :was charged with 50 ml. of n-heptane, lXl() moles of tetraneopentylchromium and 2 l0&#39; moles of ethylaluminum dichloride. The vesseland contents! were equilibratedat 4C. and exposed .to a 275 watt sunlamp positioned 12 inche fr m the vessel. sAfter&#39;Ofi hour. the lamp-wastemoved and ethylene wasintroduced to a pressure of 3.0 p-siag: and the. temperature .WasJaised-to 5 0?CrAtFter 2.B hofurs at that temperature, the .vessel wasvented, cooled arid thepolyethylenewas isolated; .lt amounted to a produetivityof 73 g; permillimole of chromium EXAMPLE 23&#39; The general procedure of Example 22 was. followed but using 2 l0&#34;&#34; moles of triethylaluminum as activator instead of the ethyialiimiiiu&#39;in dichloride used in that example. In this case the irradiation was carried out at -l0G;.for 0:7 hour under anethylene pressure of 30 p.&#39;s.&#39;i.g. The lampiuasremoved andwith the tempera tur&#39;e raised to 50C. The polymerization was continued for 2.8. hours. Theipolyethylene .so obtained amounted to a productivity of I86 g. per millimole of chromium and a-rateof 33 &#39;g./mm.ol e Cr/atmJhr.  
  f EXAMPLE 24 y The procedure of Example 22 was repeated except that the activator was trimethylaluminum in place of the ethylaluminum dichloride used in that example. The irradiation was carried out at 2 to 6C. for L2 hours, after which the lamp was removed, ethylene introduced at a pressure of 30 p.s.i.g. and the polymerizationwas carried out at C. for 1.9 hours. The polyethylene so obtained amounted to a productivity of 35 g. I per millimole of chromium and a rate of 9.2 q,./&#39;mmole Cr/atmJhr.  
 EXAMPLE 25 Example 24 v was repeated except that diisobutylaluminum hydride was used as the activator, the irradiation was carried out for 0.6 hour and the polymerization for 2.8 hours. The polyethylene so obtained amounted to a, productivity of 21 g. per millimole of chromium and a rate of 4.1 g./mmole Cr/atm./hr.  
 EXAM LE 26 32 These examples dernonstrate preparation of a .ihs&#39; QnditiQas-JQ Evade/2612 .29 and m mjum=compou d was mixed with. the silica in 300 ml. of n-heptane (15 ml. in Example 27) and reacted thermally in the darhln Example 32 the reaction was car-.  
 ried but byph toly is. the mi tur of il caandchropniumw nound. in 99 l f vhcp a e eing i d whi ss p scd o aZliwt u lamp po t one 12 chie fronmhq reactor-and in Exampl 2, .beenphotoly i an the ma eas iqn wa s d I Exa p e .3 I th chro ium compound and sil ca were mixed in pent e a d. the luen .wasr pora dr a 50C- where-- upon an immedi te react n took plac The pplymerizations wereall conducted in 300 ml. of nwh pt nc/andi under ansethylenepresvsure of 30 p.s.i.g. ,1;Tabula,ted in Table .ll-js. the data; for the preparation of the catalysts and .thepolymerization of. ethylene with each catalyst, along with the yield of polyethylene expressed .in.gramspetmillimole. of chromium and the rate (gJmmole&#39;Cr/atmJhra).  
  $5525 it; 5% 1 3i; jfz] at 3&#39;2&#34; Catalyst Preparation 4 SiO,. g. 0.25 0.50 0.50 0.50 0.50 0.50 0.50 Dried Annealed Annealed Dried Dried Annealed Dricd ISO-160C at 700C.&#34; at700C. 330C. 330C. at 700C. 200C. 16 hours Beforcusc T Before use l6 hrs. 16 hrs. Before use 4 hrs. dried 200C. dried 200C. dried at for 5 hrs.&#39; for 5 hrs. 150C. (NcopentylhCr .1... Moles. 3X10 7 2;l05 V 10&#39; 5x10&#34;! 5X10&#34;? I 7.3 l0 3.0Xl0f! TempiiC; &#34;25 &#39;Exposcd to 25&#39; &#39;25 50 25 li ht-:2 h t i Exposed to I .at 20C. light Tim&#39;cI hr. 3 l6 Heated at l9 66 i 3 &#39;80 C&#39;. for,  
 &#39; s hour.  
 TABLE II Continued Example 26 27 28 29 30 3 l 32 Ethylene Polymerization Activator None None None (C H -,Al (C H,-,) -,Al None (C H B and (C H B mmolcs l l(l&#39; lXlO&#34; each IX 10 Temp, C. 80 8O 8O 50 50 75 80 Time. hrs. 4.0 4.5 2.l 4.0 4.4 [7 0.8 Yield. I  
  g/mmolc Cr 6 l 5 364 vI90 S 1400 2120 213 Rate 1 l() 58 60 74 I87 83 165 EXAMPLE 33 5. The process of polymerizing l-olefins which com- A polymerization vessel filled with argon was charged with 50 ml. of heptane and ethylene to a pressure of 30 p.s.i.g. at 60C. There was injected 8X10 moles of tetra(neophyl)chromium and after one hour 2X10 moles of triethylaluminum was injected. Polymerization ensued after injection of the activator.  
 EXAMPLE 34 mole of chromium and the rate was 1.1 g./mmole Cr/atm./hr.  
  What I claim and desire to protect by Letters Patent is:  
  l. A polymerization catalyst comprising a tetraalkylchromium compound having the formula wherein R, and R are each selected from H and methyl and R is selected from H, alkyl, cyclohexyl, alkylcyclohexyl, cyclohexylalkyl and dimethylbenzyl; extended on an oxidic carrier material.  
  2. The catalyst of claim 1 wherein the oxidic carrier material is silica.  
  3. The catalyst of claim 2 wherein the tetraalkylchromium compound is tetra(tert.-butyl)chromium.  
  4. The catalyst of claim 2 wherein the tetraalkylchromium compound is tetra(neopentyl)chromium.  
 prises contacting at least one l-olefin with a catalyst comprising a tetraalkylchromium compound having the formula Cr I-R where R and R are each selected from H and methyl and R is selected from H, alkyl, cyclohexyl, alkylcyclohexyl, cyclohexylalkyl and dimethyl benzyl.  
  6. The process of claim 5 wherein the catalyst is activated by the addition of an organometallic activator selected from the group consisting of compounds having the formula MR,, where M is Hg, Zn, B, Al, Pb, Sn or Ge, R is a hydrocarbon radical free of ethylenic unsaturation and n is the valence of M and compounds having the. formula where R is alkyl, alkenyl, cycloalkyl, aryl, aralkyl or alkaryl andX and Y are R, halide, hydrogen or alkoxide.  
  7. The process of claim 6 wherein the activator is an organoaluminum compound.  
  8. The process of claim 5 wherein the tetraalkylchromium is extended on a oxidic carrier material.  
  9. The process of claim 8 wherein the oxidic carrier material is silica.  
 10. The process of claim 9 wherein the catalyst is activated by the addition of alkylaluminum compound.  
  11. The process of claim 9 wherein the catalyst is activated by the addition of a trihydrocarbonboron.  
  12. The process of claim 10 wherein ethylene is polymerized..  
 13. The process of claim 10 wherein propylene is polymerized.