CA2053199A1

CA2053199A1 - Process for the preparation of a polyolefin

Info

Publication number: CA2053199A1
Application number: CA002053199A
Authority: CA
Inventors: Volker Dolle; Hans F. Herrmann; Andreas Winter; Walter Spaleck
Original assignee: Individual
Current assignee: Hoechst AG
Priority date: 1990-10-11
Filing date: 1991-10-10
Publication date: 1992-04-12
Also published as: GR3024857T3; ATE155495T1; AU8578391A; AU650676B2; DE4032266A1; DE59108781D1; EP0480390B1; ES2106754T3; EP0480390A3; JPH04264110A; EP0480390A2; ZA918075B

Abstract

Abstract Process for the preparation of a polyolefin Olefins of the formula Ra-CH=CH-Rb (Ra and Rb = H or C1-C4-alkyl) are polymerized in the presence of a catalyst comprising an aluminoxane which is soluble in non-aromatic solvents and has the formula I
(I) for the linear type and/or the formula (II)

Description

-` 2~31~9 HOECHST AKTIE~GESELLSCHAFT HOE 90/F 306 Dr.L0/fe Description Proces~ for the preparation of a polyolefin The invention relates to an environ~entally friendly process for olefin polymerization, in which the use of aromatic solvents can be dispensed with by the choice of a ~pecial catalyst/cocatalyst system.

The use of metallocenes a~ catalysts in the preparation of olefin polymers in combination with aluminoxane cocataly~to is known. The cocatalyst preferably employed in thi~ proce~s i8 methylaluminoxane (cf. EP-A 185,918).
Polyolefins having high tacticity and a narrow molar mass distribution are obtained in this way. In order to control the i~otaxy or syndyotaxy of the desired polymer, a methylaluminoxane can be u~ed in which up to 40~ of the methyl group~ have been replaced by hydrogen (cf.
~P-A 421,209).

In the proce~e~ mentloned, an aromatlc oolvent, prefer-ably tolu-ne, 1~ u~ed ln the preparatlon of the partlcu-lar alumlnoxane, or tho aluminoxane ~ervlng a~ cocataly~t i~ introduced into the polymerlzatlon ve~sel in the form of ~ ~olutlon ln toluene. ln order to increaoe the activity of the metallocene employed, a ~pecial preacti-vation method i~ frequently used (EP-A 302,424). With thl~ procedure the metallocene, in turn, is dissolved in a toluene ~olutlon of the corresponding aluminoxane and employed in thl~ form a~ cataly~t for the olefln polymer-lzatlon. The u~e of, for ex~mple, allphatla ~olvent~ is precluded ~lnce the~e do not form ~table ~olutlon~ with the abovementioned aluminoxane~. However, arom4tlc solvents such as toluene are not harmle~s from the ecological and toxicological ~tandpoint ( industrial threshold limit value, TLV). Small residual amounts of such solvents are contained in the polyolefin formed and ~31~

must be removed as completely as possible since, for example, they can have an adverse effect on the polymer eharacteristies (plasticizer). Moreover, the polyolefins whieh ean be prepared by the processes deseribed, in particular polypropylene and its eopolymer6, are impor-tant as paekaging material in the foodstuffs indu~try.
Such packaging material~ should as far a~ possible not come into contact with aromntie solvents.

The ob~ect was to find a process for the preparation of I0 polyolefins havinq high tacticity, a high molar mass and a narrow molar mass distribution, with which process the use of aromatic solvents can be dispensed with without forfeiting cataly~t activity.

This ob~ect is aehieved according to the invention in that the polymerization of olefins is carried out in the presenee of specific metallocene catalysts and ~pecially ~elected aluminoxane~ a8 ¢oeatalysts.

The pre~ont invontion thue relate~ to a process for the preparation of a polyolein by homopolymerization or eopolyme~izatlon o an ole1n of the formula R--CH-CH-Rb, ln whleh R- and Rb are ldentical or dlferent and are a hydrogen atom or a Cl-C~-alkyl radleal, or R and *, togethor wlth the carbon atoms ~hich link the~, from a rlng havlng 4 to 28 carbon atoms, at ~ temperature of O~C
Z5 to 150-C, under a pre~-ure of 0.5 to 100 bar, ln solu-tlon, ln su~penslon or ln tha gas phase, in the presence of a catalyst whlch eomprises a metallocene and an alumlnoxane, wherein the alumlnoxane 18 a eompound of the formula (I~

Al - 0 ~ Al - } Al (I) Rl ~ ~ Rl for the linear type and/or of the formula (II) ` 2~53~ ~ - 3 -~ Al - o ~ (II) for the cyclic type and, in the formulae (I) and (II), Rl iB methyl or a C2-C8-~lkyl group and n i8 an integer from 2 to 50, 0.01 to 40% of the radicals Rl being a C2-C8-alkyl group. `

Alkyl is straight-chain or branched alkyl, preferably (C3-C~)alkyl and in particular isobutyl. The letter n is preferably a number from 5 to 40. Preferably, 0.01 to 35%
and in partlcular 3-12% of the radicals R1 are a C2_CB_ alkyl group.

The lnventlon also relates to the polymers and copolymers prepared by the process described and to the u~e of the ~lumlnoxanes accordlng to the lnvention as cocataly~ts in the preparation of polyolefins by the ~aid process.

The procloe ~tructure of the alumlnoxanes 18 not known and to thlo extont the particular method of preparatlon lo al~o to bo u~-d for thelr charactorlzatlon. Mlxtures of varlou~ alumlnoxanes can also be uoed for the purpose accordlng to the lnventlon, a~ cocat&lyst.

The preparatlon of the compounds I and II can be carrled out ln varlous wayo.

One posslblllty lo the careful additlon of water to a dllute oolutlon of a mixture of AlMoa and AlRa (Me-methyl, R-(C2-C~)alkyl), thlo solutlon and the water being lntro-duced, in omall portlons ln each case, lnto a largeramount of an lnert sol~ent whlch has been lnitlally introduced, w~itlng for the end of the evolutlon of ga~
between addltlons ln each case. The AlMe3~AlF~ rstlo 1~ to be chosen ln accordance wlth the compo~ltion of the desired aluminoxane.

2 ~

In another process, finely powdered copper sulfate pentahydrate is suspended in benzine and, in a glass flask under inert gas at about -20-C, ALMe3 + AlR3 are added in an amount such that approximately 1 mol of CuSO~-SH20 is available per 4 Al atoms. After slow hydro-lysis with elimination of alkane, the reaction mixture is left to stand at room temperature for 24 to 48 hours, the mixture having to be cooled if appropriate 80 that the temperature does not rise above 30-C. The aluminoxane dissolved in benzine ia then filtered off from the copper ~ulfate and the solution iB concentrated in vacuo. It is assumed that in the ca~e of this preparation process the aluminoxanes of low molecular weight conden~e to form higher oligomer~. The solution can also be used as such.

~urthermore, the aluminoxanes ~ccordinq to the invention are obtalned if a mixture of AlNe3lAlR3 (preferably Al(i-butyl)3) are reacted with aluminum salts containing water of cry~tnllization, preferably aluminum ~ulfate, at a temperature of -20 to lOO-C in an inert allphatlc sol-~ent, preerably heptane or a benzine fraction having a bolllng range of 100-120'C or 140-170-C. With this proce~ the ratio by volume of ~olvent to the aluminum alkyl~ used 1~ ltl to S0~1 - prefer~bly 5zl - and the reactlon time, whlch can be controlled by elimlnatlon of the alkane~ 1 to 200 hour~ - preferably 10 to 40 hour~.
,, , ~ , , The alumlnum ~alts containing water of cry~tallization which are u~ed are preferably those which have ~ high content of water of cry~tallization. Hydrated alumlnum ~ulfate iB particularly preferred, in partlcular the compound~ ~12( SO~ )a 16H20 and Al2(SO~)a-18H20 with the particularly hlgh content of water of ary~talllz~tion of, re~pectively, 16 and 18 mol of H20/mol of Al2(SO~)a.

A further v~riant for the preparation of aluminoxanes comprises dis~olving a mixture of AlMe3+AlR3 in the suspending agent, which has been initially introduced 2 ~

into the polymerization ves~el, prefer~bly in liguid nomers, in heptane or a benzine fraction, and then re~cting the aluminum compound~ with w~ter In principle, it is also possible to obtain the ~luminox-~nes according to the invention from ~ corresponding~luminum tri~lkyl containing different alkyl sub~titu-ents, such ~8, for example, AlNe~R, by the abovementioned proces~Qs ~ore th~n two different aluminum tri~lkyls can ~l~o serve ~8 starting subst~nces In addition to these, there ~re further proce~ses disclo~ed in the liter~ture ~hich ~re suitable for the preparation of the ~luminox-~ne~

Both in the c~e of tho proce~-e~ mentioned for obt~ining the aluminoxanes and in the ca~e of the method, which is ~till to be de~cribed, for the pre~ctiv~tion of the met~llocene cataly~t, according to the invention aromatic compound~ aro not u~ed a~ olvent~ Suit~ble olvent~
are, for example, alkanes of the formula C~H~z where m 2 6 or o-called industrial benzine or die-el oil fractlon- having ~ boiling range of, for example, 100-120 C or 140-170 C 5O1vent~ to be mentioned in p~rticul~r are tho~e of the ex~ol type~ (Exxon Chemical~) The ready-to-u~e cat~ly~t ~olution~ which are employed in the polymerization proce~ o cont~in the~e 2g allph~tic ~olvent~

~etallocene~ which can be u~ed are various compounds of thi~ type, for ex~mple compound~ of the formula III

/ ~ 2 (III) \ ¦ ~ R3 In formul~ III, ~P 1- ~ metal ~elected from the group comprising titanlum, zlrconlum, h~fnlum, vanadium, nloblum, t~ntalum and chromlum, preferably zlrconlum and 2~3~3 hafnium.

R2 and R3 are identical or different and are a hydrogen atom, a Cl-C10-, preferably Cl-C3-alkyl group, a Cl-C10-, preferably Cl-C3-alkoxy group, a C6-C10-, preferably C6-C8-aryl group, a C0-ClO-, preferably C~-Ca-aryloxy group, a C2-C10-, prefer~bly C8-C~-alkenyl group, a C,-C~0-, prefer-~bly C,-C10-arylalkyl group, a C~-C~0-, prefer~bly C,-Cl8-alkylaryl group, a C0-C~O-, pr~ferably Ca-Cl8-arylalkenyl group, or a halogen atom, preferably chlorine.

R~ and R~ are identical or different and are a mononuclear or polynuclear hydrocarbon radical whlch together with the central atom M1 can form a sandwlch structure.

Preferably R~ and R5 are fluorenyl, indenyl and cyclo-pentadienyl, it being po~ible for the parent radical al80 to c~rry additional ~ub~tituent~.

R~ 1~ a ~lngle-membered or multl-membered brldge, which llnk~ th~ radlcal~ R~ and R~ and 1~

-M2_ , -M2_M2_ , -M2_CR29- , -C- , -O-M2_ , _C--C-~ BR7, - AlR7, -Ge-, -Sn-, -0-, -S-, ~ S0, - SO2, - NR7, - C0, - PR7 or - P(o)R7, where R7, R~ and R~ are identical or different ~nd are a hydrogen atom, a halogen atom, prefer~bly chlorlne, a Cl-C10-, preferably Cl-Ca-alkyl group, ~n partlcul~r a methyl group, a C1-C10-fluoroalkyl group, preferably a CFa group, a C~-C~0-fluoroaryl group, preferably a pentafluorophenyl group, a C~-C10-, preferably C6-C8-aryl group, a C1-C10-, preferably C1-C~-alkoxy group, in particular a methoxy group, a C2-C10-, preferably C2-C~-alkenyl group, a C~-C~0-, preerably C~-C10-arylalkyl group, n C~-C~0-, preferably Ca-Cl2-arylalkenyl group, a C~-C~0-, preferably C~-C12-alkylaryl group or the radical -CH2-M2(CH3J 3 ~ or R6 and R7 or R~ and ~3~9 RA, in each ca~e together with the atoms which link them, form a ring.

i~ ~ilicon, germanium or tin, preferably silicon or germanium.

R~ i~ preferably ~CR'RA, -SiR7R~, -GeR7R~, -O-, -S-, -SO, -PR7 or -P(o)R7.

TheJe metallocene~ are chiral. For the purpose according to the inventlon, a~ cataly~t, both the racemate and the particular enantiomer~ are ~uitable. The last-mentioned compound~ can be obtained by known methods for racemate ~plitting.

Tho metalloceno~ de~cribod above can be prepared in accordance with the following general reaction w hemes 2~3~

H2R4~b utylLi-- HR4Li X_R6_X HR4-R6-R5H 2-butylLi H2R5+butylLi ~ HRSLi LiR4_R6_R5Li MlC14 .

R~/ M1 ~ R~ Ml~ R3L1. R~

(X = Cl, Br, I, O- tosyl) ~r H2R4 + butylLi_ ~IR4Li R\ /R a, HR4Li~R7R8C
R6 b, H20 ~ R4H
I

2 ~butylLi ~RS
[~ R C~ 4]Li2 MlC14 R7~ / ' ,Cl C Ml R \ ' Cl R2Li / ' i R3Li ~ R ~ / ~ l~R

R8 \ ll \R3 2 0 ~
g Suitable metallocene~ are, for example, bisindenyl-ethylene-zirconium dichloride, bi~indenyl-ethylene-hafniumdichloride,bisindenyl-dimethylsilylene-zireonium dichloride, bi~indenyl-dimethylsilylene-hafnium dichlor-ide and also (arylalkylidene)-(9-fluorenyl)(cyclopentadi-enyl)zirconium dichloride, (diarylmethylene)(9-fluor-enyl)(cyclopentadienyl)zireonium dichloride and (dialkyl-methylene)(9-fluorenyl)(cyclopentadienyl)zirconium diehloride and the eorresponding hafnium eompounds.

Partlcularly suitable eataly~ts for the proeess according to the invention are the metallocenes listed in the illustrative examples.

It i~ possible to preactivate the metallocene using an aluminoxane of the formula (I) and/or (II) before use in the polymerization reaction. By this means the polymer-lzation aetivity is elearly inereased and the particle morphology of the polymer is improved.

Tho proaetlvatlon of the transitlon metal eompound is e~rried out in ~olution. Preferably the met~lloeene 1~
dl~olved ln ~ ~olutlon of the aluminoxane in one of the lnert solvent~ already mentloned.

The eoneentr~tlon of the aluminoxane in the solution i~
ln the range from about 1% by weiqht up to the ~aturation limlt, preferably from 5 to 30% by weight, in oach ease ba~ed on the total solutlon. The metallocene can be used in the same concentration, bnt it 18 preferably u~ed in an ~mount of 10-~ - 1 mol per mol of alumlnoxane. The prèaetivatlon time 1B 5 mlnutes to 60 hours, preferably 5 to 60 mlnutes. The preaetlvatlon 1~ carrled out at a temperature of -78-C to lOO-C, preferably 0 to 70-C.

The polymerlzation 1~ earrled out ln a known manner ln ~olution, in suspen~lon or ln the gas phase, eontlnuously or discontlnuously, ln one or more stage~, at a tempera-ture of 30 to 150-C, preferably 30 to 80-C. Olefin~ of 20~3~

the formula R'-CH=CH-Rb are polymerized, or their mixtures are polymerized in order to prepare copolymers. In thi~
formula R and Rb are identical or different and are a hydrogen atom or an alkyl radical having 1 to 28 carbon atoms. R and * can, however, al~o form, together with the carbon atoms which link them, a ring having 4 to 28 carbon atoms. Examples of ouch olefins are ethylene, propylene, but-l-ene, hex-l-ene, 4-methylpent-1-ene, oct-l-ene, norbornene, norbornadiene, pentene, hexene or octene. In particular propylene is polymerized.

For the polymerization, the metallocene compound is used in a concentration, baoed on the tranoition metal, of 10-3 to 10-7, preferably 10-~ to 10-~ mol of tranoition metal per dma of oolvent or per dm3 of reactor volume. The lS aluminoxane 1~ uoed in a concentration of 10-~ to 10-~ mol, preferably 10-~ to 10-2 mol per d~3 of solvent or per dm3 of reactor volume. In principle, however, higher cancen-trationo are ~loo poooible. The metalloeene uoed io at le~ot one compound of the formula III. Mixtures of oevoral eompoundo of the formula III or mixtureo of loom ro are al~o poo~ible.

Sf neoeo~ary, hydrogen io added ao molar maoo regulator.
The total preo~ure in the polymerlzation oyotem io 0.5 to 100 bar. Polymerlz~tlon ln the preooure range of 2 to 64 bar, whieh lo of partieular intereot industrlally, is proferred.

If the polymerization io carried out ao ~uspenolon or oolution polymerlz~tion, an lnert oolvent euotomary for the Zlegler low-preooure proee-o lo uoed. For ex~mple, the polymerlzatlon lo earrled out ln an allphatie or eyeloallphatie hydroearbon; aliphatle or eyeloaliphatle hydroearbons which may be mentioned are~ for ex~mple, butane, pentane, hexane, heptane, loooetane, eyelohexane and methyleyelohexane.

Furthermore, a benzine fraction or hydrogenated diesel oil fraction can be used. The polymerlzation i8 prefer-ably carrled out in the liqu$d nomer.
If inert solvents are used, the monomers are metered in in the gas or liquid form.
If only one monomer is used as suspending agent, the comonomer or the comonomer~ are metered in in gas or liquid form.
Furthermore, it is possible to carry out the polymeriza-tion in a mixture of different monomers as suspending agent; a further monomer can then be metered in in liquld or gas form. When ethylene is used it is advantageou~
initially to introduce some of the ethylene and to meter in the remainder during the polymerization.

The polymerization time i~ ~rbitr~ry, since the catalyst ~y~tem to be u~ed according to the invention displays only a ~light time-dependent fall in the polymerization actlvity.

The proce~ a¢cordlng to the lnvention is ~l~o dlstln-gui~hed ln that the metallocene~ u~ed are highly stable to temperature, ~o that they can be omployed wlth hlgh actlvity ev n at temperature~ of up to 90-C. Moreover, the alumlnoxane~ ~ervlng a~ coc~taly~t~ can be added ln lower concentratlon~ than hlthorto. Flnally, lt 1~ now po~ le to u~e alumlnoxane~ w~thout ~romatlc ~olvent~.

The followlng examples are lntended to lllustrate the lnventlon. In these example~
yndyotactic index, determined by 13C NMR
~pectro~copy ~ otactic lndex, determlned by ~3C NMR
~poctro~copy M~ - w~ight-average mol~r ma~ lg/moll~ the mol~r mas~es were determlned u~lng gel permeatlon chromatography N~/M~ - polydlsper~lty 2~3 ~ ~

Example 1 A dry 16 dm3 vessel was flushed with nitrogen and filled with 10 dm3 of liguid propylene. 35 cm3 of isobutylmethyl-aluminoxane, dissolved in heptane (= RMA0, corre~ponding S to 40 mmol of Al, average degree of oligomerization n - 30, about 10% of the Rl radical ~ isobutyl) were then added and the batch was stirred for 15 minutes at 30-C~

In parallel, 3.B mg of (Ind)2SiMe2ZrCl2 were dis~olved in 17.5 cm3 of RMAO (- 20 mmol of Al) and preactivated by leaving to ~tand or ~tirring for 15 minutes.

Thi~ ~olution wa~ then added to the ve~el. The polymer-ization ~y~tem was brought to a temperature of 70-C ~nd the polymerization ~tarted. The polymerization wa~
~topped after 60 minute~ by cooling the reactor and letting down.

1.5 kg of polypropylene were obtained. The activity Wa8 thu~ 400 kg PP/g metallocene/h.

Th following analytical data were determined for the polymert M~ - S2000 g/mol, N~/M~ - 2.1, II - 92~.

~he following ~xample~ 2-12, the re~ult~ of which are given in the following table, were carried out analog-ou~ly to th~ proce~ method.

~3~

o 't U

. N
11~ N t.) .
-_I O O O O O O O O O
O O O O O O O o O O
~ ~ O O O O O O ~ O O
~O d' Il~ ~ O O ~ ~ U) d' _I

O O O O ~ O O ~,D O
0 ~ o o~
U

~ ~ ~ U~
~I N ~1 0 u') _ O ~

.
u o o o o o o c~ o o - ~

~ 5 ~" 5 ~ 5 ~ 5 ~ 5 ~ 5 ~ 5 ~ ol U ~ N o ~ ~ U c,a ~ æ H 14 U ~

~ o E~ ~ Z

2~3~9 ~C ~; N N N
U ~ U ~
o Cr~
H dP H ~` Pl ' ' ,~ N N

Q O o O
, ~ ,~ o æ

~ ~ o o ~ ~:
~ 0~ ~
o~
o ,~:~
~ t~CL

C~ o o ~I

N 1 ~ ~ ~N

c 0 ~
O ~ C1~ N
~1 0~3 ~ H H
U --_ _ --I

O ~ O
W Z

- 2~3~

Example 13 A dry 16 dm3 resetor w~s flushed with nitrogen ~nd filled with 10 dm3 of liquid propylene 30 em3 of isobutylmethyl-~luminoxane, di~solved in heptane (eorresponding to 40 mmol of Al, av~r~ge d~gree of oligomerization n - 20) were then added ~nd the b~teh was ~tirred for 15 minutes ~t 30 C

In parallel, 10 4 mg (O 024 mol) of dimethylm~thylene(9-fluorenyl)(eyelopent~dienyl)zireonium dichloride were di~olved in lS em3 of i~obutylmethylaluminoxane (20 mmol of Al), preaet$v~ted by le~ving to ~tand for 15 minutes and then added to the ~e~el Polymeriz~tion was lnltl~lly earrled out for 30 minute~ at a polymerization t~mperature of 70'C (~tage 1, polymer 1) and the polymer-lz~tlon temperature wa~ then lowered to 50 C The pres-~ure wa~ ad~u~ted to an ab~olute pres~ure of 31 bar by in~eeting ethylone During the 30 minute polymerization, thl~ pre~ur- wa~ kept eon~tant by metering in additional thyl-ne (~tag 2, polym r 2) 0 75 kg of polymer having ~n MFI 230/5 of 135 dg mln~l and a VN of 83 c~3/q wa-obtalned Tho ethylene eontent of the polymer ~ 17 44 by ~elght Meltlng point ~ 124/134 C, cry~talllzatlon temperature - 84 C, T~ - -59 5 C and 3 7 C (two qla~
tr~n~ltlon~, lt being po~ible to a~ign the hlgher value to the ~yndyotaetie homopolymer matrix (polymer 1) and the lo~er value to the ~yndyotactic copolymer rubber (polymer 2)) The ~yndyotactic lndex of the polypropylene con~tituent ~a~ 94 7% In polymer 2 35 4% of the ethylene ~a~ l~o-l~ted (n~-l), 8 3% of the ethylene wa~ lncorporated ~lth n~-2 and 65 3~ of the ethylene wa~ lneorporated ln block~
(n~3); the polypropylene block~ had a ~yndyotaetlc ~trueture "

16 20~31~
Example 14 A dry veseel h~ving a capacity of 16 dm3 was flushed with nitrogen and filled with 10 dm3 of liquid propylene 30 cm3 of isobutylmethylaluminoxane, diesolved in heptane (~ RNA0, eorreeponding to 40 mmol of Al, average degree of oligomerization n ~ 20) were then added and the batch was stirred for lS min at 30 C In parallel, 85 6 mg (0 160 mmol) of rac-dimethylsilylbisindenylhafnium diehlorlde were dissolved in 15 emJ of RNAO solution (- 20 mmol of Al) and preaetivated by leaving to ~tand for 15 minutes The solution was then added to the veesel The polymerization ~ystem was heated to a temperature of 60'C, kept at this temperature for 5 h and eooled to 50 C
ln the couree of 10 min Ethylene was paeeed into the u~pension until the boiling pre~ure of the nomer mlxture had rleen to 35 bar Thi~ pres~ure wae maintained for th remalnlng 60 mln reaetlon tlme by feeding in additlonal thylene 1 40 kg of block copolym~r having an MPI 230/5 of 4 5 dg m~nl were obtalned The polymer had a VN of 320 cm3/g 12 9~ by w lght of the polymer had formed by polymerlza-tlon of ethyl-ne By reeryetalllzatlon from the benzlne mlxture, 60% of cry-talllzable fractions, ba~ed on the total polymer, havlng a VN of 282 em3/g were obtained 0%, ba~ed on the block copolymer, of a rubber-like mass having an ethylene eontent of 324 by weight and a VN of 364 emJ/g were obtained from the mether liquor by pre-cipitation with acetone The experimental re~ult~ show that, de~pite a sterlcally more demanding eocatalyst, which has dletinctly dlfferent ~olution char~aterlstlcs compared wlth the prlor art, for high polymer qu~lity eurprieingly no loee of activ$ty of the catalyet $e to be observed

Claims

1. A process for the preparation of a polyolefin by homopolymerization or copolymerization of an olefin of the formula Ra-CH=CH-Rb, in which Ra and Rb are identical or different and are a hydrogen atom or a C1-C14-alkyl radical, or Ra and Rb, together with the carbon atoms which link them, form a ring having 4 to 28 carbon atoms, at a temperature of 0°C to 150°C, under a pressure of 0.5 to 100 bar, in solution, in suspension or in the gas phase, in the presence of a catalyst which comprises a metallocene and an aluminoxane, wherein the aluminoxane is a compound of the formula (I) (I) for the linear type and/or of the formula (II) (II) for the cyclic type and, in the formulae (I) and (II), R1 is methyl or a C2-C8-alkyl group and n is an integer from

2 to 50, 0.01 to 40% of the radicals R1 being a C2-C8-alkyl group.

2. The process as claimed in claim 1, wherein, in the formulae I and/or II, R1 is methyl or a C3-C5-alkyl group.

3. The process as claimed in claim 1 or 2, wherein, in the formulae I and/or II, R1 is methyl or isobutyl.

4. The use of an aluminoxane of the formula (I) (I) for the linear type and/or of the formula (II) (II) for the cyclic type and, in the formulae (I) and (II), R1 is methyl or a C2-C8-alkyl group and n is an integer from 2 to 50, 0.01 to 40% of the radicals R1 being a C2-C8-alkyl group, for the homopolymerization or copolymeriza-tion of olefins as claimed in claim 1.

5. A polyolefin prepared by the process as claimed in one or more of claims 1 to 3.

6. A polyolefin as claimed in claim 5, which comprises polypropylene.