Ziegler-natta catalyst systems containing specific organosilicon compounds

Catalyst systems of the Ziegler-Natta type contain, as active components PA0 a) a titanium-containing solid component in whose preparation a titanium compound, a compound of magnesium, a halogenating agent and an electron donor component are used, PA0 b) an aluminum compound and PA0 c) as a further electron donor component, an organosilicon compound of the formula (I) EQU R.sup.1 R.sup.2 Si(OR.sup.3).sub.2 (I) where R.sup.1 is C.sup.1 -C.sub.10 -alkyl or C.sub.3 -C.sub.8 -cycloalkyl, excluding sec-butyl, R.sup.2 is sec-butyl and R.sup.3 is C.sub.1 -C.sub.8 -alkyl. The catalyst systems are particularly suitable for the preparation of polymers of C.sub.2 -C.sub.10 -alk-1-enes.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention relates to novel catalyst systems of the 
Ziegler-Natta type containing, as active components, 
a) a titanium-containing solid component in whose preparation a titanium 
compound, a compound of magnesium, a halogenating agent and an electron 
donor component are used, 
b) an aluminum compound and 
c) as a further electron donor component, an organo-silicon compound of the 
formula (I) 
EQU R.sup.1 R.sup.2 Si(OR.sup.3).sub.2 (I) 
where R.sup.1 is C.sub.1 -C.sub.10 -alkyl or C.sub.3 -C.sub.8 -cycloalkyl, 
excluding isopropyl, sec-butyl and tert-butyl, R.sup.2 is sec-butyl and 
R.sup.3 is C.sub.1 -C.sub.8 -alkyl. 
The present invention furthermore relates to the preparation of polymers of 
C.sub.2 -C.sub.10 -alk-1-enes with the aid of these catalyst systems, the 
polymers obtainable hereby and films and moldings of these polymers. 
DESCRIPTION OF THE RELATED ART 
Catalyst systems of the Ziegler-Natta type are disclosed in, inter alia, 
EP-B 14523, EP-A-23425, EP-A 45 975, EP-A 195 497, EP-A 250 229 and U.S. 
Pat. No. 4,857,613. These systems are used in particular for polymerizing 
alk-1-enes and contain, inter alia, compounds of poly-valent titanium, 
aluminum halides and/or alkylaluminums, as well as electron donor 
compounds, for example silicon compounds, ethers, carboxylates, ketones 
and lactones, which are used on the one hand in conjunction with the 
titanium compound and on the other hand as a cocatalyst. 
To ensure economical polyalk-1-ene production, such catalyst systems must 
have, inter alia, a high productivity. This is understood as being the 
ratio of the amount of polymer formed to the amount of catalyst used. It 
is also necessary for the polymers obtainable to be highly stereospecific, 
i.e. the amount of noniso-tactic molecular structures in the homopolymers 
should not exceed from 2.0 to 3.0%. 
These two aims together can be realized only to a limited extent by the 
prior art. For example, EP-A 86 473 discloses a catalyst system in which 
carboxylates are used as the electron donor compounds within the 
titanium-containing solid component and in general organic silicon 
compounds are used as further electron donor compounds and which has 
satisfactorily high productivity but is unsatisfactory with regard to the 
stereospecificity of the resulting polymers. Furthermore, EP-A-171 200 
describes a Ziegler-Natta catalyst system which has, inter alia, 
carboxylates as constituents of the titanium-containing solid component 
and in general organic silicon compounds as further electron donor 
compounds. These catalyst systems permit, inter alia, the preparation of 
polypropylene having high stereospecificity but do not have the 
satisfactorily high productivity. 
In addition to these properties which are particularly important for the 
processing of the polymers, a low halogen content of the polyalk-1-ene is 
also of importance in order to permit such materials to be used in 
conjunction with materials susceptible to corrosion. For this purpose, it 
is necessary in particular substantially to reduce the halogen content of 
the polymer. Furthermore, for process engineering reasons it is important 
for the polyalk-1-enes to have good morphological properties, in 
particular a very small fraction of very small particles. 
It is an object of the present invention to provide an improved catalyst 
system with which the disdvantages described can be substantially remedied 
and which makes it possible to prepare polymers of C.sub.2 -C.sub.10 
-alk-1-enes with high productivity, which polymers possess high 
stereospecificity, good morphological properties and a very low halogen 
content. 
SUMMARY OF THE INVENTION 
We have found that this object is achieved by the novel catalyst systems 
stated in the claims. 
For the preparation of the titanium-containing solid component a), in 
general halides or alkoxides of trivalent or tetravalent titanium are used 
as the titanium compounds, the chlorides of titanium, in particular 
titanium tetrachloride, being preferred. Advantageously, the 
titanium-containing solid component contains a finely divided carrier, 
silicas and aluminas as well as aluminum silicates of the empirical 
formula SiO.sub.2.aAl.sub.2 O.sub.3, where a is from 0.001 to 2, in 
particular from 0.01 to 0.5, having proven useful for this purpose.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferably used carriers have a particle diameter of from 0.1 to 1000 
.mu.m, in particular from 10 to 300 .mu.m, a pore volume of from 0.1 to 
10, in particular from 1.0 to 5.0, cm.sup.3 /g and a specific surface area 
of from 10 to 1,000, in particular from 100 to 500, m.sup.2 /g. 
Furthermore, compounds of magnesium, inter alia, are used in the 
preparation of the titanium-containing solid component a). Suitable 
compounds of this type are magnesium halides, magnesium aryls, magnesium 
alkyls and alkoxymagnesium and aryloxymagnesium compounds, magnesium 
dichloride, magnesium dibromide and di-C.sub.1 -C.sub.10 -alkyl-magnesium 
compounds being particularly used. A halogenating agent, preferably 
chlorine, hydrogen chloride, bromine or hydrogen bromide, is also used in 
the preparation of this component. 
In addition to the trivalent or tetravalent titanium compounds and, if 
required, the carrier, the magnesium compound and the halogenating agent, 
electron donor components, for example mono- or polyfunctional carboxylic 
acids, carboxylic anhydrides, carboxylates, ketones, ethers, alcohols, 
lactones and organophosphorus and organosilicon compounds, are also used 
in the preparation of the titanium-containing solid component a). 
Preferred electron donor components within the titanium-containing solid 
component a) are, inter alia, diesters of 3- or 4-membered, unsubstituted 
or substituted cycloalkyl-1,2-dicarboxylic acids and monoesters of 
unsubstituted or substituted benzophenone-2-carboxylic acids. The alcohols 
conventionally used in esterification reactions, including C.sub.1 
-C.sub.15 -alcohols, C.sub.5 -C.sub.7 -cyclo-alcohol, which in turn may 
carry C.sub.1 -C.sub.10 -alkyl groups, and C.sub.6 -C.sub.10 -phenols, are 
employed as hydroxy compounds for these esters. 
Further preferably used electron donor components within the 
titanium-containing solid component include phthalic acid derivatives of 
the formula II 
##STR1## 
where X and Y are each chlorine or C.sub.1 -C.sub.10 -alkoxy, in 
particular C.sub.1 -C.sub.4 -alkoxy, or together form oxygen. 
The titanium-containing solid component can be prepared by conventional 
methods. Examples of these are described in, inter alia, EP-A 45 975, EP-A 
45 977, EP-A 86 473, EP-A 171 200, GB-A 2 111 066 and U.S. Pat. No. 
4,857,613. 
In the preparation of the titanium-containing solid component a), the 
following three-stage process is preferably used. 
In the first stage, a solution of a magnesium-containing compound in a 
liquid alkane is first added to a finely divided carrier, preferably 
silica or SiO.sub.2.aAl.sub.2 O.sub.3, where a is from 0.001 to 2, in 
particular from 0.01 to 0.5, after which this mixture is stirred for from 
0.5 to 5 hours at from 10.degree. to 120.degree. C. From 0.1 to 1 mol of 
the magnesium compound is preferably used per mol of the carrier. A 
halogen or a hydrogen halide, in particular chlorine or hydrogen chloride, 
is then added, with constant stirring, in at least a two-fold, preferably 
at least a five-fold, molar excess, based on the magnesium-containing 
compound. 
A C.sub.1 -C.sub.8 -alcohol, in particular ethanol, a halide or an alkoxide 
of trivalent or tetravalent titanium, in particular titanium 
tetrachloride, and an electron donor compound, in particular a phthalic 
acid derivative of the general formula (II), are then added. From 1 to 5, 
in particular from 2 to 4, mol of alcohol, from 2 to 20, in particular 
from 4 to 10, mol of the trivalent or tetravalent titanium and from 0.01 
to 1, in particular from 0.1 to 1.0, mol of the electron donor compound 
are used per mol of magnesium of the solid obtained in the first stage. 
The solution is stirred at from 10.degree. to 150.degree. C. and the solid 
substance thus obtained is then filtered off and is washed with a liquid 
alkane, preferably with hexane or heptane. 
Suitable aluminum components b), in addition to trialkylaluminum compounds 
whose substituents are each of 1 to 8 carbon atoms, are compounds in which 
one alkyl substituent is replaced with alkoxy or halogen, for example 
chlorine or bromine. Trialkylaluminum compounds whose alkyl groups are 
each from 1 to 8 carbon atoms, for example trimethyl-, triethyl- or 
methyldiethylaluminum, are preferably used. 
According to the invention, an organosilicon compound of the general 
formula (I) 
EQU R.sup.1 R.sup.2 Si(OR.sup.3).sub.2 (I) 
where R.sup.1 is C.sub.1 -C.sub.10 -alkyl or C.sub.3 -C.sub.8 -cycloalkyl, 
excluding isopropyl, sec-butyl and tert-butyl, R.sup.2 is sec-butyl and 
R.sup.3 is C.sub.1 -C.sub.8 -alkyl, is used as the further electron donor 
component c). 
Preferably used organosilicon compounds of the formula (I) are those in 
which R.sup.1 is branched C.sub.3 -C.sub.8 -alkyl, in particular branched 
C.sub.3 -C.sub.6 -alkyl, and R.sup.3 is C.sub.1 -C.sub.6 -alkyl, in 
particular C.sub.1 -C.sub.4 -alkyl. Particularly preferred organosilicon 
compounds are those in which R.sup.1 is isobutyl or isopropyl. 
Among these compounds, dimethoxyisobutyl-sec-butylsilane, 
diethoxyisobutyl-sec-butylsilane, diiso-propoxyisobutyl-sec-butylsilane, 
diisobutoxyisobutyl-sec-butylsilane, dimethoxyisopropyl-sec-butylsilane 
and diethoxyisopropyl-sec-butylsilane are particularly noteworthy. 
Preferably used catalyst systems are those in which the atomic ratio of 
aluminum from the aluminum compound b) to titanium from the 
titanium-containing solid component a) is from 10:1 to 800:1, in 
particular from 20:1 to 200:1, and the molar ratio of the aluminum 
compound b) to the electron donor compound c) used according to the 
invention is from 1:1 to 100:1, in particular from 2:1 to 80:1. The 
catalyst components may be introduced into the polymerization system 
individually in any order or as a mixture of the components. 
The novel catalyst system is particularly suitable for polymerizing C.sub.2 
-C.sub.10 -alk-1-enes. C.sub.2 -C.sub.10 -alk-1-enes in this context are 
understood as being in particular ethylene, propylene, but-1-ene, 
pent-1-ene, hex-1-ene, hept-1-ene or oct-1-ene or mixtures of these 
C.sub.2 -C.sub.10 -alk-1-enes, preferably used monomers being propylene or 
but-1-ene. The novel catalyst system is particularly suitable for the 
homopolymerization of propylene or the copolymerization of propylene with 
minor amounts of ethylene, but-1-ene, pent-1-ene, hex-1-ene or mixtures of 
these monomers. 
The preparation of polymers of C.sub.2 -C.sub.10 -alk-1-enes with the aid 
of the novel catalyst system can be carried out in the conventional 
reactors used for polymerizing propylene, either batchwise or, preferably, 
continuously, inter alia as a suspension polymerization or, preferably, as 
a gas-phase polymerization. Suitable reactors include continuously 
operated stirred reactors which contain a fixed bed of finely divided 
polymer which is usually kept in motion by suitable stirring apparatuses. 
Of course, the reaction may also be carried out in a number of reactors 
connected in series. 
The polymerization reaction is advantageously carried out at from 
20.degree. to 150.degree. C., preferably from 40.degree. to 100.degree. 
C., and from 1 to 100, preferably from 10 to 50, bar. The average 
residence times of the reaction mixture during the polymerization with the 
aid of the novel catalyst system are usually from 1 to 10, in particular 
from 1 to 5, hours. The molecular weight of the polyalk-1-enes formed can 
be regulated by adding regulators conventionally used in polymerization 
technology, for example hydrogen. It is also possible for inert solvents, 
for example toluene or hexane, or inert gases, such as nitrogen or argon, 
to be present. 
The average molecular weights of the polymers prepared with the aid of the 
novel catalyst system are from 10,000 to 1,000,000 and the melt flow 
indices are from 0.1 to 100, preferably from 0.2 to 50, g/10 min, measured 
in each case according to DIN 53,735 at 230.degree. C. and 2.16 kg. The 
melt flow index corresponds to the amount of polymer which is forced, in 
the course of 10 minutes at 230.degree. C. and under a weight of 2.16 kg, 
out of the test apparatus standardized according to DIN 53,735. 
The novel catalyst system has high productivity, particularly in gas-phase 
polymerizations. The polymers obtainable in this manner have high 
stereospecificity, a low chlorine content and a very small fraction of 
very fine particles (&lt;0.25 mm). The polymers prepared using this catalyst 
system are suitable in particular for the production of films and 
moldings. 
EXAMPLES 
Example 1 
a) Preparation of the titanium-containing solid component (1) 
In a first stage, a solution of n-butyloctyl-magnesium in n-heptane was 
added to SiO.sub.2 which had a particle diameter of from 20 to 45 .mu.m, a 
pore volume of 1.7 cm.sup.3 /g and a specific surface area of 330 m.sup.2 
/g, 0.3 mol of the magnesium compound being used per mol of SiO.sub.2. The 
solution was stirred for 30 minutes at 40.degree. C. and then cooled to 
20.degree. C., after which 10 times the molar amount, based on the 
organomagnesium compound, of hydrogen chloride was passed in. After 60 
minutes;3 mol of ethanol per mol of magnesium were added to the reaction 
product with constant stirring. This mixture was stirred for 30 minutes at 
80.degree.C., after which 7.2 mol of titanium tetrachloride and 0.5 mol of 
di-n-butyl phthalate dissolved in ethylbenzene were added, the amounts 
each being based on 1 mol of magnesium. Stirring was then carried out for 
1 hour at 100.degree. C. and the solid substance thus obtained was 
filtered off and washed several times with ethylbenzene. 
The solid product obtained therefrom was extracted for 3 hours at 
125.degree. C. with a 10% strength by volume solution of titanium 
tetrachloride in ethylbenzene. Thereafter, the solid product was isolated 
from the extracting agent by filtration and was washed with n-heptane 
until the extracting agent contained only 0.3% by weight of titanium 
tetrachloride. 
The titanium-containing solid component contained 3.6% by weight of Ti, 
7.7% by weight of Mg and 27.9% by weight of Cl. 
b) Polymerization 
50 g of polypropylene powder (melt flow index: 10 g/10 min at 230.degree. 
C. and 2.16 kg, according to DIN 53,735), 10 mmol of triethylaluminum (in 
the form of a 1 molar solution in n-heptane), 10 1 of hydrogen, 93.2 mg of 
the titanium-containing solid component prepared according to Example 1a) 
and 1 mmol of dimethoxyisobutyl-sec-butylsilane were initially taken at 
30.degree. C. in a 10 1 steel autoclave provided with a stirrer. The molar 
ratio of the aluminum component to the organosilicon compound used 
according to the invention was 10:1. Thereafter, the reactor temperature 
was increased to 70.degree. C. in the course of 10 minutes and the reactor 
pressure was brought to 28 bar by forcing in gaseous propylene, after 
which polymerization was carried out with an average residence time of the 
reaction mixture of 1.5 hours. The monomer consumed was continuously 
replaced with fresh monomer. 
1,430 g of a propylene homopolymer having a melt flow index of 11.3 g/10 
min at 230.degree. C. and 2.16 kg (according to DIN 53,735) were obtained. 
The productivity of the catalyst system, which is defined as the ratio of 
the amount of polymer formed to the amount of titanium-containing solid 
component, the heptane-soluble fraction, which is a measure of the 
proportion of noniso-tactic structural units, the fraction of very fine 
particles (&lt;0.25 mm) and the chlorine content of the polymer are listed in 
the Table below. 
Example 2 
Propylene was polymerized using the same catalyst system and under the 
reaction conditions as described in Example 1, the reaction being carried 
out in a suspension at 37 bar and 80.degree. C. instead of 28 bar and 
70.degree. C. 
Example 3 
Propylene was polymerized using the same catalyst system and under the 
reaction conditions as described in Example 1, 1 mmol of 
dimethoxyisopropyl-sec-butylsilane being used instead of 1 mmol of 
dimethoxyisobutyl-sec-butylsilane, as the further electron donor component 
c). 
1,435 g of a propylene homopolymer having a melt flow index of 12.8 g/10 
min at 230.degree. C. and 2.16 kg (according to DIN 53,735) were obtained. 
The further results are shown in the Table below. 
TABLE 
______________________________________ 
Example 1 
Example 2 Example 3 
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Productivity (g of 
15,340 20,200 15,400 
propylene/g of titanium- 
containing solid component) 
Heptane-soluble fractions 
2.2 1.7 2.1 
(% by weight) 
Fraction of very fine par- 
1.0 0.5 0.8 
ticles &lt;0.25 mm (in %) 
Chlorine content of 
18 14 18 
the polymer (ppm) 
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