A stereospecific catalyst system intended for the polymerization of olefins

Abstract: A good activity and stereospecifity have been achieved by a catalyst system intended for the polymerization of olefins comprising a procatalyst based on a titanium compound, an organoaluminium cocatalyst and an organosilane compound, the organosilane compound having the following formula (I) in which R is a lower alkyl, R′ is an alkyl, R″ is a substituent donating electrons, n = 1, 2, or 3, m = 0, 1, or 2, and n + m ≦ 3.

Description: The present invention relates to a catalyst system intended for the polymerization of olefins comprising a procatalyst based on a titanium compound, an organoaluminium cocatalyst and an organosilane compound. Generally, the Ziegler-Natta catalyst system is used for the polymerization of olefins, which system essentially consists of a so-called procatalyst and a cocatalyst. A procatalyst is a component which is based on a compound of a transition metal belonging to any of the groups IVA-VIII of the periodic table of elements (Hubbard, IUPAC 1970). A cocatalyst, on the other hand, is a component based on an organometallic compound of a metal belonging to any of the groups IA-III(A) of the periodic table of elements, (Hubbard, IUPAC 1970). To the catalyst system usually also belongs electron donor compounds improving and modifying the catalytic properties. An internal donor is used as a part of the procatalyst to modify and improve its catalytic effect. An external donor, on the other hand, is used together with the cocatalyst of procatalyst to improve, among other things, the stereospecificity of the catalyst system. Many external donors of this kind improving the stereospecifity are known in the field. EP patent specifications 231,878 and 261,961 disclose the preparation of a procatalyst from magnesium dichloride, diheptylphthalate and titanium tetrachloride, an alternative coating of the procatalyst composition obtained with an propylene prepolymer and using the procatalyst obtained together with t-butylmethyl dimethoxysilane and triethylaluminium for the stereospecific polymerization of the propylene. EP patent specification 045,977 discloses the use of a procatalyst, formed of magnesium dichloride, titanium tetrachloride and an internal donor, together with triethylaluminium and phenyl triethoxysilane for the polymerization of the propylene. EP patent specification 267,576 discloses the use of a procatalyst of the same type together with an alkyl- phenyl- or tolylmethyoxy- or -ethoxy silane and an organoaluminium compound for the polymerization of olefins. The patent specifications EP 250,229, DE 3,644,368, US 4,710,482, JP 63-182,306 and JP-63-37104 also represent the same type of technology. EP-A-0258788 and EP-A-0356841 disclose the manufacture of polymers of propylene materials with a Zeigler-Natta catalyst system comprising (1) a titanium component from titanium, magnesium, chlorine and a phthalic acid source (2) an alkyl aluminium and (3) a silane compound as cocatalyst. The silane compound is substituted with a phenyl ring, which ring is substituted by e.g. a hydrocarbon moiety such as methyl, ethyl, isopropyl or isobutyl. EP-A-0282341 describes a catalyst formed from (a) a solid titanium catalyst component containing magnesium, titanium, halogen and a polycarboxylic acid ester, (b) an organoaluminium compound and (c) an organosilicon compound such as cumyl methyl dimethoxysilane. The aim of the present invention is to achieve a new catalyst system intended for the polymerization of olefins which is better than previously suitable for the preparation of stereospecific polymers. Simultaneously, the highest possible activity of the catalyst is aimed at. These goals have now been achieved by the new catalyst system intended for the polymerization of olefins, characterizing of which mainly is what has been related in the characterizing clause of Claim 1. Thus, it has been realized that the better stereoselectivity and activity than previously has been achieved by an external organosilane donor having the following formula I: in which R is methyl or ethyl, R' is alkyl, R" is a phenyl ring substituted which is tert. butyl, phenyl or phenoxy, n=1, 2 or 3, m=0, 1 or 2, and n+m≤3. The aromatic substituent R" in the formula is, according to one embodiment, a tertiary butyl group. According to another embodiment R" is a phenyl group. According to a third embodiment group R" is a phenoxy It has also been noted that the organosilane compound in question is a particularly good external donor, if the group R" is in the para-position of the benzene ring. The symbol n of the formula I is preferably 2 or 3 and still more preferably 2. The symbol m is preferably either 1 or 2. The sum m + n is preferably 3. When more than one substituent type shown by the formula (n, m and/or 4-m-n ≥ 1) has been attached to the silicon atom of the formula I, the groups R, R' and R" in question can be either of different kind or similar. As far as the efficiency of the external electron donor is concerned it is advantageous if the substituent of the organosilane compound R is ethyl or methyl, preferably methyl. Particularly preferable organosilane compounds that can be used as external donors are 4-t-butylphenyl trimethoxysilane: di(4-t-butylphenyl) dimethoxysilane: biphenyl trimethoxysilane: methyl(phenoxyphenyl) dimethoxysilane: As mentioned above the catalyst system according to the present invention comprises a procatalyst based on a titanium compound, an organoaluminium cocatalyst and an organosilane compound. The procatalyst component used in the invention usually is a titanium compound supported by a solid magnesium compound insoluble in hydrocarbon, to which may still be attached an internal electron donor. Such procatalysts are usually formed by bringing a compound of 4 valent titanium, an organic internal electron donor and a magnesium compound to react with each other. Suitable magnesium containing compounds are magnesium halides, reaction products of magnesium halide and an organic or metalorganic compound, magnesium alcoholates or magnesium alkyls. The most preferable magnesium compound is magnesium dichloride. Titanium compounds usable in the present invention are halides and alkoxy halides of 4 valent titanium, the alcoholate groups having from 1 to 20 carbon atoms. Most preferable are the titanium tetrahalides and particularly titanium tetrachloride. Suitable internal donors to be used in the procatalyst are organic compounds containing one or more oxygen, nitrogen, sulphur or phosphorus atoms. Accordingly, the electron donor can be selected from the group comprising aliphatic or aromatic carboxylic acids, aliphatic or aromatic alkyl esters of carboxylic acids, ethers, aliphatic or aromatic ketones, aliphatic or aromatic aldehydes, aliphatic and aromatic alcohols, aliphatic and aromatic acid halides, aliphatic and aromatic nitriles, aliphatic and aromatic amines as well as aromatic phosphines. As cocatalyst can be used any organometallic compound of a metal belonging to any of the groups IA-III(A) of the periodic table of elements. Typical metals are magnesium, zinc, and aluminium, the last-mentioned of which being the most preferable. Most preferable are the trialkyl aluminiums, such as triethylaluminium. In the following we present some examples for the illustration of the invention. Example 1 The organoaluminium compound triethyl aluminium and an external donor, 4-t-butyl trimethoxysilane (II), were mixed into 20 ml of dried heptane, the Al:donor molar ratio being 10. After 8 minutes 25 mg of a solid procatalyst was added to the mixture, whereby the Al:Ti molar ratio became 200. The procatalyst, the titanium content of which was 2.6% by weight, had been prepared according to Example 1 of EP-A-279818 (corresponding to patent FI-80055), and consisted of a MgCl 2 support, having diisobutyl phthalate as an internal donor and Ticl 4 as transition metal compound. Next the catalyst was transferred to a one-liter nitrified polymerization reactor prepared of stainless steel, after which hydrogen was added to the reactor so that the partial pressure became 0.3 bar. After this 300g of liquid propylene was conducted to the reactor. The temperature was maintained at 10°C for five minutes for the prepolymerization of the catalyst, after which the temperature was raised to the polymerization temperature 60°C. The polymerization time was 45 minutes. The activity of the catalyst was 7.6kg of polypropylene/g of catalyst in one hour. The polypropylene obtained had a round form and it was freely flowing, and its isotacticity was 96.4%, by which is meant the portion of polypropylene of the whole polymer amount that does not dissolve in the boiling heptane. The intrinsic viscosity of the polymer at 135°C, when the solvent was decaline, was 2.5dl/g. Example 2 The polymerization was otherwise carried out as in Example 1, but biphenyl trimethoxysilane (VI) was used as the external donor. Hereby, the activity of the catalyst was 7.1kg of polypropylene/g of catalyst in one hour. The isotacticity of the polymer was 96.5% and the intrinsic viscosity 2.41dl/g. Example 3 The polymerization was otherwise carried out as in Example 1, but di(biphenyl) dimethoxysilane was used as the external donor. Hereby, the activity of the catalyst was 7.0kg of polypropylene/g of catalyst in one hour. The isotacticity of the polymer was 92.5% and the intrinsic viscosity 2.31dl/g. Example 4 The polymerization was otherwise carried out as in Example 1, but methyl(phenoxyphenyl) dimethoxysilane (V) was used as the external donor. Hereby, the activity of the catalyst was 6.7kg of polypropylene/g of catalyst in one hour. The isotacticity of the polymer was 98.3% and the intrinsic viscosity 2.67dl/g. A comparison example The polymerization was otherwise carried out as in Example 1, but as the external donor was used methylphenyl diethoxy-silane. the structure of which otherwise corresponds to the external donors of the present invention (cf. Example 4) except that the phenyl is not a substituted one. Hereby, the activity of the catalyst was 5.9kg of polypropylene/g of catalyst in one hour. The isotacticity of the polymer was 94.0% and the intrinsic viscosity 1.98dl/g.

Claims: A catalyst system for the polymerization of olefins comprising a procatalyst based on a titanium compound, an organoaluminium cocatalyst and an organosilane compound, characterized in that the organosilane compound has the following formula (I) in which R is methyl or ethyl, R' is alkyl, R" is a phenyl ring substituent which is tert. butyl, phenyl or phenoxy, n=1, 2 or 3, m=0, 1 or 2 and n+m≤3. A catalyst system according to claim 1, characterized in that R" is a tertiary butyl group. A catalyst system according to claim 1, characterized in that R" is a phenyl or a phenoxy group. A catalyst system according to any one of the preceding claims, characterized in that R" is in the para position of the benzene ring. A catalyst system according to any one of the preceding claims, characterized in that n is 2 or 3. A catalyst system according to any one of the preceding claims, characterized in that m is 1 or 2. A catalyst system according to any one of the preceding claims, characterized in that R is methyl. A catalyst system according to any one of the preceding claims, characterized in that R' is methyl. A catalyst system according to claim 1, characterized in that the organosilane compound is 4-t-butylphenyl-trimethoxysilane, biphenyl-trimethoxysilane, or methyl(phenoxyphenyl)dimethoxysilane. A catalyst system according to any one of the preceding claims, characterized in that the procatalyst comprises a 4 valent titanium compound on a magnesium halide carrier, preferably TiCl 4 on a MgCl 2 carrier. A catalyst system according to any one of the preceding claims, characterized in that the organoaluminium cocatalyst is a trialkyl aluminium, preferably triethyl aluminium.

Inventors: HAERKOENEN MIKA, KULO ARVO, SEPPAELAE JUKKA, HAERKOENEN, MIKA, KULO, ARVO, SEPPAELAE, JUKKA, Härkönen, Mika, Seppälä, Jukka 
Applicants: BOREALIS AS, BOREALIS A/S
Application year: 1991
Main classification: C08F4
IPC codes: C08F10, C08F4