The invention relates to a method for the homo- or copolymer¬ ization of ethylene with the aid of the catalytic action of a τι-cyclopentadienyl transition-metal compound and an aluminoxane compound.

Ethylene polymerization is commonly carried out by using a Ziegler-Natta catalyst system which comprises a so-called pro- catalyst and a cocatalyst. The procatalyst is based on a com¬ pound of a transit-ion metal belonging to any of groups IVA - VIII (Hubbard) of the Periodic Table of the Elements, and the cocatalyst is based on a compound of a metal belonging to any of groups 1(A) - III(A) (Hubbard) of the Periodic Table. Among the procatalysts, a separate group is formed by the metallocene-type transition-metal compounds, i.e. compounds which have one or several unsaturated rings, such as a cyclo- pentadienyl ring, linked with a π-bond to the transition me al.

US patent publication 3 242 099 discloses a catalyst system intended for the polymerization of olefins, in which system bis-cyclopentadienyltitanium dichloride is combined with an oligomeric aluminoxane compound.

US patent publication 4 404 344 discloses a method for the preparation of homo- and copolymers of ethylene and propylene by polymerizing one or several monomers by means of a catalyst system comprising bis-σyclopentadienylzirconium dimethyl and a lower alkylaluminoxane. It is stated in this publication that ethylene can be copolymerized with propylene, 1-butene, 1- hexene or α-, ω-dienes.

EP-69951 and US-4 542 199 disclose the polymerization of Cx-do olefins in the presence of a catalyst system which comprises bis-cyclopentadienylzirconium dichloride or bis-cyclopenta-

dienylzirconiummonomethyl monochloride and a linear or cyclic methylaluminoxane. It is also stated in the publication that this catalyst system is highly suitable for the control of polyethylene density by copolymerizing in the polyethylene chain longer-chained α-olefins, such as propylene, 1-butene an 1-hexene, at maximum 10 % by weight. No correlation between th alkyl chain length in the α-olefins and the activity and mono¬ mer selectivity of the catalyst system is presented.

EP-260 999 discloses a method for the homo- or copolymerizatio of ethylene by means of a cyclopentadienyl transition-metal compound and an aluminoxane compound. The transition metal may be a transition metal of group IVB or VB, the cyclopentadienyl ring may be either unsubstituted or substituted, and addition¬ ally there may be one or several organic groups and one or several halogen atoms bound to the transition-metal compound. The aluminoxane may be a linear or cyclic aluminoxane oligomer substituted with a lower alkyl. According to this publication, the catalyst system may also be used for preparing olefin copo ly ers, and in particular copolymers of ethylene and C ₃ -C _lβ -α- olefins. The comonomer concentration in the polymer can also be controlled by the selection of a cyclopentadienyl transition-metal compound of a suitable type. The publication does not mention any correlation between the length of the alkyl chain of the α-olefin and the activity or monomer selec¬ tivity of the catalyst.

In JP publications 63 092 621, 303 519, 1 101 315, 313 386, 2 084 405 and 2 218 706, ethylene is copolymerized with C ₃ -C ₁₀ - α-olefins by using bis-cyclopentadienylzirconium dichloride an aluminoxane as the polymerization catalyst. In the first- mentioned five publications, the carrier used for the catalyst system is either an inorganic oxide or a granulated polymer. I the last-mentioned publication the cocatalyst is a mixture of aluminoxane and trialkylaluminum. These publications do not present any correlations between the alkyl chain length of the

α-olefin comonomer and the activity or monomer selectivity of the catalyst system.

The object of the present invention is to provide, for the homo- or copolymerization of ethylene with the aid of the cata lytic action of a π-cyclopentadienyl transition-metal compound and an aluminoxane compound, a method in which the said cata¬ lyst system has maximally high activity. It is also an object of the invention to provide for the copolymerization of ethyl¬ ene a method in which the catalyst system used has maximally high selectivity, especially when monomer units containing lon alkyl chains are desired for the copolymer. A further object o the invention is an ethylene homo- or copolymerization system in which, when the said catalyst system is used, the polymeri¬ zation can be carried out at a relatively low temperature and pressure, and preferably in the presence of an alkane solvent. It is also an object of the invention to provide ethylene ter- polymers in which the termonomers are ethylene, C ₃ -C _1D -α-olefin, and an ethylene-unsaturated monomer which contains at minimum 10 carbon atoms^ in its side chain.

The above-mentioned objects have now been achieved by a new method for the homo- or copolymerization of ethylene with the aid of the catalytic action of a π-cyclopentadienyl transition metal compound and an aluminoxane compound, the method being characterized mainly in what is stated in the characterizing clause of Claim 1. It has thus been realized that the homo- or copolymerization of ethylene can be enhanced by the use of the said catalyst system, if a compound according to Formula (I) i allowed to take part in the polymerization

CH-,=CHR (I)

where R stands for a hydrocarbon group having at minimum 8 carbon atoms. The said long-chain ethylene-unsaturated compoun thus enhances the activity of the catalyst system comprising a

π-cyclopentadienyl transition-metal compound and an aluminoxane compound and increases its monomer selectivity, especially when ethylene is copolymerized (di- or terpolymerized) with a com¬ pound according to Formula (I). Compared with smaller-molecule ethylene-unsaturated compounds, the said compound provides clearly higher activity values and selectivity values for the catalyst system.

It is advantageous if group R in the compound according to Formula (I) has approximately 8-20, preferably 10-20, and most preferably 14-20 carbon atoms. In addition, it is advantageous if the compound according to Formula (I) is 1-alkene. Some examples of usable alkeneS are decene, undecene, dodecene, tridecene, tetradecene, pentadecene, hexadecene, heptadecene, octadecene, nonadecene and eicosene. Their branched isomers are also usable.

According to an important embodiment of the invention, the compound according to Formula (I) is used in larger amounts in the polymerization mixture in order to produce an ethylene copolymer in which the proportion of monomer units correspond¬ ing to the compound according to Formula (I) is higher. By the word higher is meant in this case that in copolymerization the catalyst system used in the invention favors, more than do the conventional catalyst systems based on a TiCl ₄ /MgCl ₂ procata- lyst and a trialkylaluminum cocatalyst, the bonding of the co¬ monomer according to Formula (I) to the ethylene polymer chains being formed.

Such selectivity based on the length of the monomer chain in the catalyst system is exploited in the present invention, for example, by adding a compound according to Formula (I) to a solution or bulk polymerization mixture at a rate of 0.10 - 1.00, preferably 0.20 - 1.00, and most preferably approximately 0.40 - 1.00 mol/1 in order to produce an ethylene copolymer in which the proportion of monomer units corresponding to the

compound of Formula (I) is, respectively, more than 6 %, pref¬ erably more than 13 %, and most preferably more than approxi¬ mately 30 % by weight.

As already stated, one advantage of the compound according to Formula (I) is its activating effect on the catalyst system made up of a π-cyclopentadienyl transition-metal compound and an aluminoxane compound. If it is desired only to activate the catalyst, it is advantageous to use the compound according to Formula (I) in small amounts to enhance the homo- or copolymer ization of ethylene. According to one embodiment, in solution or bulk polymerization of ethylene, a compound according to Formula (I) is used at a rate of approximately 0.01- 10 mo1/1. In a system in which the polymerization temperature __.s 70 °C, ethylene pressure 3.8 bar, reaction time 10 min, and the Al/Zr ratio 1000, even with a 1-decene concentration of 0.05 mol/1 the activity is doubled, and with a concentration of 0.10 mol/ the activity is more than tripled. Considerable activation of the catalyst is also achieved by using 1-hexadecene. Both with 1-decene and with 1-hexadecene, the catalyst system is acti¬ vated more than with 1-butene. Thus there is clear experimenta evidence that surprising activity as compared with lower 1- alkenes is obtained with the use of a compound according to Formula (I) which has at minimum 10 carbon atoms in group R.

The polymerization parameters of the method according to the invention may in principle be any whatsoever, as long as a homo- or copolymer of ethylene is produced in the polymeriza¬ tion and a compound according to Formula (I) participates in one way or another in the polymerization. The polymerization temperature may be, for example, approximately -50 - +200 °C, and preferably approximately +50 - +100 °C. The polymerization time may be approximately 5-40 minutes and preferably approx¬ imately 10-20 minutes.

It,is advantageous to carry out the polymerization in a solven

or as bulk polymerization. A preferred solvent is liquid alkane, the most preferred is Ce-Ciz alkane.

The molar ratio of the metal of the aluminoxane compound to that of the π-cyclopentadienyl transition-metal compound may vary greatly. In general the rule is that aluminum is used in considerably larger amount than the transition-metal compound. According to one embodiment, the said molar ratio of the metals ranges from 100,000:1 to 10:1, preferably from 2000:1 to 200:1.

By a π-cyclopentadienyl transition-metal compound is meant a catalytically active transition-metal compound in which at least one cyclopentadienyl ligand is linked to the transition metal by a π-bond. Such a ligand is very stable, and it can be regarded as constituting a six-electron aromatic anion C ₅ H _S . Owing to its aromatic stability it may also be substituted. These compounds are also called metallocenes.

According to one embodiment, the π-cyclopentadienyl transition- metal compounds have the following general formula (II)

CpjiRiY ₀ (II)

where Cp is π-cyclopentadienyl or substituted π-cγclopenta- dienyl, R ¹ is an organic group, Y is a halogen, and m is an integer 1-3, n is an integer 0-3 and o is an integer 0-3.

It is advantageous if Cp is π-cyclopentadienyl, i.e. unsub- stituted. R ¹ is, when the group is used, preferably a lower alkyl, and most preferably methyl. Respectively, Y is preferab¬ ly chlorine. M is preferably zirconium Zr or titanium Ti, pref¬ erably zirconium Zr. It is also advantageous if is 2, n is 0 or 1, and o is 1 or 2. Some preferred π-cyclopentadienyl transition-metal compounds are bis-π-cyclopentadienylzirconium- monomethyl monochloride and bis-π-cyclopentadienylzirconium

dichloride, and the most preferred is bis-π-cyclopentadienyl- zirconium dichloride.

Although the π-cyclopentadienyl transition-metal compounds we view as being the most preferable are presented above, it is also possible to use other compounds of corresponding type. Such compounds are listed, for example, in EP application 303 519 from page 3, line 59 to page 4, line 31, and in EP application 260 999 on page 4, lines 14-30. Both applications are thus appended as references to the present application.

The second catalyst component in the polymerization method according to the invention is an aluminoxane compound. It has preferably the following general formula (III)

(A1(R ² )0) _P (Ilia)

or

R ² (A1(R ² )0) _P A1R ² (Illb)

where R ² stands for an organic group and p is an integer 1-50. Formula (Ilia) is applicable when the structure of the alumin¬ oxane compound is cyclic, and Formula (Illb) is applicable whe the structure of the aluminoxane compound is linear.

Group R ² in an aluminoxane compound according to Formula (III) is preferably an alkyl group having 1-5 carbon atoms, and most preferably methyl, p in the formula is preferably such that th aluminoxane is at least an oligomer, and most preferably it is an integer 4-20.

The aluminoxane used in the invention may be prepared in a number of ways, for example by contacting water with tri- alkylaluminu or by contacting trialkylaluminum with a hydrate

salt, such as hydrated copper sulfate or iron sulfate. When th aim is to prepare at least oligomers of the aluminoxane, the aluminoxane is preferably prepared by using hydrated iron(II) sulfate or hydrated copper sulfate. In this case a dilute solu tion of trialkylaluminum in toluene, benzene or xylene is treated with FeS0 ₄ '7H ₂ 0 or with CuSC ^• 5H ₂ 0. The molar ratio of hydrated sulfate to trialkylaluminum is usually 1:5 - 1:10 and the reaction temperature is within the range -40 - +60 °C, in which case methane gas is released in the reaction. The product is usually both linear and cyclic aluminoxane having an oligo- merization degree of approximately 6 or more when the reaction is successful.

The catalyst system used in the method according to the inven¬ tion may be homogenous or heterogenous. In a heterogenous sys¬ tem, a carrier may be used both for the π-cyclopentadienyl transition-metal compound and for the aluminoxane compound, or alternatively, the π-cyclopentadienyl transition-metal compound and a carrier treated, for example impregnated, with the alum¬ inoxane compound can be added to the polymerization mixture. Suitable carriers include silica, alumina, magnesia, zirconia, magnesium silicate, alkylated silicates, and certain polymers such as granular polyethylene.

It is, however, advantageous in the present invention to use a homogenous catalyst system comprising a π-cyclopentadienγl transition-metal compound and an aluminoxane compound, in which the polymerization and catalysis are preferably carried out in a hydrocarbon solvent.

Although the catalyst system used in the method according to the invention is based on a π-cyclopentadienyl transition-metal compound and an aluminoxane compound, it may also contain other catalyst components and promoters. These include other transi¬ tion-metal compounds and aluminum compounds and possible elec¬ tron donors ^" According to one embodiment, the cocatalyst used

is a mixture of an aluminoxane compound and trialkylaluminum.

It has also been realized in connection with the invention tha it is especially advantageous to carry out terpolymerization, i.e. the copolymerization of three comonomers, based on ethyl¬ ene monomer, if a compound according to Formula (I) takes part in the reaction. According to one preferred embodiment, ter¬ polymerization of ethylene, C ₃ -C ₁₀ -α-olefin and a compound ac¬ cording to Formula (I) is carried out. The advantage is partly based on the fact that between the compound according to For¬ mula (I) and the catalyst system used in the invention there prevails an effect favoring the compound according to Formula (I) as a comon>. r. At the same time the compound according to Formula (I) also has an activating effect on the catalytic system so that it _. produces more terpolymer.

In the said terpolymerization it is preferable to maintain the ethylene pressure at a value of 3.0 - 4.5 bar, .and most prefer¬ able to maintain it at a value of 3.6 - 4.0 bar. In this case it is preferable to carry out the terpolymerization in a solu¬ tion or as bulk polymerization, in which case the initial con¬ centration of C ₃ -Cιo-α-olefin is within a range of 0.10 - 0.50 mol/1 and the initial concentration of the compound ac¬ cording to Formula (I) is within a range of 0.05 - 0.50 mol/1. When the initial concentration of C ₃ -C _1Q -α-olefin is within a range of 0.10 - 0.20 mol/1 and the initial concentration of the compound according to Formula (I) is within a range of 0.37 - 0.45, a terpolymer is produced in which the proportion of mono¬ mer units corresponding to the compound according to Formula (I) is in the order of magnitude of approximately 25 % r>y weight. So 1? rge a proportion of the monomer unit correspondin to the compound according to Formula (I) is not achieved by using a conventional TiCl-»/MgCl ₂ /R ₃ Al catalyst system.

A number of examples are presented below to illustrate the invention.

Examples 1-21

Materials

The bis-π-cyclopentadienylzirconium dichloride (Cp ₂ ZrCl ₂ ) and the methylaluminoxane (MAO) were of a commercial grade, and they were not purified separately. Polymerization-grade ethyl¬ ene, 1-butene, 1-decene and 1-hexadecene, as well as n-heptane serving as a medium, were purified by feeding them through a column series in order to remove residual moisture and oxygen. The MgCl ₂ /TiCl ₄ catalyst system used as the reference was a ty¬ pical Ziegler-Natta catalyst on a carrier, and its titanium concentration was 7 % by weight. The aluminum alkyl compounds serving as the reference cocatalyst were used as a 10 wt.-% heptane solution (Schering AG) .

Polymerization

Bi- and terpolymerizations of ethylene, 1-butene, 1-decene and 1-hexadecene were carried out in a 500-ml autoclave at a tem¬ perature of 70 °C for 10 minutes, by using n-heptane as the reaction medium. The comonomers and catalysts were fed into the reactor at the beginning of the polymerization. The reactor pressure was maintained at the desired level by means of con¬ tinuous ethylene feed, the ethylene pressure in the reactor being 3.8 bar. The molar ratio Al/Zr was 1000. When 1-butene was used as a comonomer, the comonomer conversions were in dipolymerization 16-45 % and in terpolymerization 19-48 %, and when 1-decene was used as a comonomer they were in dipolymeri¬ zation 24-32 % and in terpolymerization 25-41 %.

Characterization of the polymers

Figures 1-4 show graphical representations of the results of the experiments of the examples.

Figure 1 depicts a typical ¹³ C-NMR spectrum of a terpolymer of

ethylene, 1-butene and 1-decene (Example 14),

Figure 2 depicts the total activity of the copolymerization as a function of the comonomer concentration of the feed, Figure 3 depicts the 1-decene concentration of the polymer as function of the 1-decene concentration of the reaction medium; the points indicated by solid squares represent a Cp ₂ ZrCl ₂ cat¬ alyst and the points indicated by empty squares represent the reference catalyst, i.e. a TiCl ₄ /MgCl ₂ catalyst, and Figure 4 depicts the dependence of the total activity on the 1 decene concentration in the reactor, with different 1-butene concentrations in ethylene/1-butene/l-decene polymerization.

The compositions of the ethylene/butene, ethylene/1-decene and ethylene/1-hexadecene dipolymers and of the ethylene/1-butene/ 1-decene terpolymers were determined by "C-NMR spectrometry by using a Jeol SGX-14-tγpe NMR spectrometer. A typical terpolyme spectrum (Example 14) is depicted in Figure 1.

The melting points and enthalpies were determined from the pea of a DSC curve measured by means of a PL-DSC instrument. The DSC measurements were carried out with a heating rate of 10 °C/min. The molecular weights, i.e. molar masses, and the molecular weight distributions (MWD) were measured bv using a Waters ALC/GPC150 instrument equipped with 2 Schodex mixed-bed columns with a polystyrene exclusion limit of 5x1 ^~~ and one Schodex column with a polystyrene exclusion limit of 2x10°, at 135 °C. 1,2,4-trichlorobenzene with a flow rate of 1.0 ml/min was used as the solvent.

Ethylene/1-butene, ethylene/1-decene, and ethylene/1-hexadecen dipolymerizations were carried out by using a Cp ₂ ZrCl ₂ /MAO com¬ bination as the catalyst. The polymerization results and the chemical and physical basic properties of the polymers are shown in Tables 1, 2 and 3. Table 1 and Figure 2, which depict the total activity of polymerization as a function of the co¬ monomer concentration in the feed, show that catalyst activity

increases considerably when a small amount of a comonomer, either 1-butene or 1-decene, is introduced into the ethylene polymerization. Furthermore, it is observed that with 1-decene at even quite low concentrations, i.e. concentrations of ap¬ proximately 0.1 mol/1, considerable increase in activity is achieved. The fact that the activity of a Cp ₂ ZrCl ₂ /MAO catalyst increases more the longer the comonomer chain, has not been previously observed or disclosed.

When a shift is made to an even longer comonomer chain, the activity increases drastically, and according to Table 3 the catalyst activity yielded by 1-hexadecene at a comonomer con¬ centration of 0.10 mol/1 is approximately triple as compared with the activity of 1-butene comonomer. At the same time it i seen that the activating effect of longer-chain 1-alkene is great, specifically at low comonomer concentrations in the feed.

Figure 3 shows that the proportion of 1-decene in the copolyme continues to increase with an increase of the 1-decene con¬ centration in the feed. When the concentration of 1-decene is 0.4 mol/1, the proportion of decene in the copolymer reaches a value of approximately 30 % by weight.

For reference, polymerization was carried out in the same con¬ ditions by using a prior-art catalyst system in which case, with the same 1-decene concentration in the fee (0.4 mol/1) , a 1-decene proportion of only 6 % by weight in th copolymer was obtained. It is thus evident that a Cp ₂ ZrCl ₂ /MAO catalyst system can be used for increasing the proportion of longer-chain α-olefins in copoly ers and, respectively, when a Cp ₂ ZrCl ₂ /MAO catalyst is used in copolymerization, longer-chain α-olefins can be added at higher rates than .previously to pro¬ duce copolymers in which the proportion of longer-chain α- olefins is high.

The terpolymerization of ethylene with 1-butene and 1-decene was also investigated by using the same catalyst in the same polymerization conditions. Figure 5 shows that in the ter¬ polymerization the same phenomena occurred as in the dipolymer ization, i.e. the catalyst activity increased with an increase in the concentration of 1-decene in the feed; this occurred at various concentrations of 1-butene. It can also be seen that, when the concentration of 1-butene was lower (0.1 mol/1), the activity of the catalyst increased substantially with an in¬ crease of the concentration of 1-decene in the feed, but when the concentration of 1-butene was higher (0.4 mol/1), the cor¬ responding activity increase was smaller.

Table 2 shows a few properties of the terpolymers. The same phenomena occur in terpolymers as in dipolymers, i.e. with Cp ₂ ZrCl ₂ /MAO catalysts th' lengthening of the comonomer chain increases the activity ι low concentrations, and that with th said catalyst system it is possible to incorporate into the terpolymer larger amounts of α-olefin, and in particular long- chain α-olefin.

Table 1 Polymerization conditions and results

Example Comonomer concentration in feed Activity Physical form 1-butene 1-decene xlO-6 of polymers ^a mol/1 mol/1 g/mol Zr.h

polymerization temperature = 70 °C, ethylene pressure = 3.8 bar, [Zr] = 6.8 μm, [Al]/[Zr] = 1000, reaction time 10 min, a: I = insoluble polymer during polymerization 3 = soluble polymer

Table 2 Basic properties of certain dipolymers and terpolymers

Polymer composition Example 1-butene 1-decene Mw*10 ^-3 MWD T °C Λ ^~~ _£ % t. % wt. g/mol peak range j/g

a = average value of multiple peaks

Table 3 Conditions and results of ethylene dipolymenzation carried out with 1-hexadene

\-* σ _*

* ) Catalyst = MgCl ₂ /TiCl ₄ +TEA; Al/Ti=200; titanium concentration 7.2 % by weight; reaction medium n-heptane (300 ml, in a 0.5 dm ³ reactor)

**) Calibrated with a wide molecular weight distribution of polyethylene