Preparation of homopolymers and copolymers of α-mono-olefins by means of a Ziegler catalyst system
The present invention derives from a process for the preparation of homopolymers and copolymers of C 2  -C 6  -α-monoolefins by polymerizing the monomer or monomers at from 30° to 200° C., under a pressure of from 0.1 to 200 bar, by means of a Ziegler catalyst system comprising 
     (1) a titanium-containing catalyst component and 
     (2) an aluminum compound of the formula 
     
         AlA.sub.3-n X.sub.n 
    
     where 
     A is a C 1  -C 18  -hydrocarbon radical, preferably a C 1  -C 12  -alkyl radical or C 3  -C 12  -alkenyl radical, and especially a C 2  -C 8  -alkyl radical, 
     X is chlorine, bromine or hydrogen, preferably chlorine or hydrogen and 
     n is from 0 to 2, preferably from 0 to 1, and especially 0, with the provisos that the atomic ratio of titanium from catalyst component (1) to aluminum from catalyst component (2) is from 1:0.1 to 1:500, preferably from 1:0.2 to 1:200, and that 
     (1.1) to prepare the catalyst component (1) 
     (1.1.1) a titanium compound (I) of the formula 
     
         TiCl.sub.3.z(AlCl.sub.3) or Cl.sub.m Ti(OB).sub.4-m 
    
     where z is from 0 to 0.5, especially from 0.31 to 0.35, m is from 0 to 3, especially from 0 to 2, and B is C 1  -C 18  -alkyl, especially C 2  -C 8  -alkyl, and 
     (1.1.2) a magnesium alcoholate (II) of the formula 
     
         Mg(OD).sub.2 
    
     where D is a monovalent C 1  -C 18  saturated-aliphatic and/or aromatic hydrocarbon radical, preferably a monovalent C 1  -C 10  saturated-aliphatic hydrocarbon radical or phenyl and especially C 1  -C 4  -alkyl, 
     (1.1.3) with or without, but advantageously with, a metal chloride (III) of the formula AlCl 3 , ZnCl 2  or MnCl 2 , preferably AlCl 3 , in the weight ratio of titanium compound (I) to magnesium alcoholate (II) of from 1:200 to 1:0.2, preferably from 1:1 to 1:100, and in the weight ratio of titanium compound (I) to metal chloride (III) of from 1:0 to 1:20, preferably from 1:0 to 1:5, are milled, preferably dry, with one another for from 1 to 200, preferably from 5 to 100, hours, under a milling acceleration of from 30 to 70 m/s 2 , to form a milled product (IV). 
     Processes of this type are known, and typical examples may be found in British Patent No. 1,532,332 or U.S. Pat. No. 3,941,760. 
     At the center of the processes mentioned, and of other parallel processes, there is a titanium-containing catalyst component (1) prepared in a specific manner and hence constituting a specific embodiment. 
     The various embodiments of the titanium-containing catalyst component are aimed at achieving particular objectives, for example the following: 
     (a) Catalyst systems which can give an increased yield of polymer, namely systems which have a higher productivity, ie. systems in which the amount of polymer formed per unit weight of catalyst system (1) is increased. 
     (b) Catalyst systems by means of which less or no halogen is introduced into the polymer, this being achievable (b 1 ) by increasing the yield as in (a) and/or (b 2 ) by employing a titanium-containing catalyst component which contains very little or no halogen. 
     (c) Catalyst systems which display their advantageous effects even at relatively low temperatures; this can be of importance in, for example, dry phase polymerization. 
     (d) Catalyst systems by means of which the morphological properties of the polymers are influenced in a certain way, for example in the sense of giving a uniform particle size and/or reducing the proportion of fines and/or giving a high bulk density; this can be of importance in, for example, the technical control of polymerization systems, in working up the polymers and/or in respect of the processability of the polymers obtained. 
     (e) Catalyst systems which are simple and safe to prepare and easy to handle, for example systems which can be prepared in (inert) hydrocarbon auxiliary media. 
     (f) Catalyst systems which make it possible, where the polymerization is carried out using a molecular weight regulator, such as hydrogen, to manage with relatively small amounts of such a regulator; this can, for example, be important as regards the thermodynamics of the process. 
     (g) Catalyst systems tailored for specific polymerization processes, for example those intended to suit either the specific peculiarities of suspension polymerization or the specific peculiarities of dry phase polymerization. 
     According to experience gathered hitherto, there are, amongst these numerous objectives, some which can only be achieved by special embodiments of the titanium-containing catalyst component if other objectives are lowered. 
     Under these circumstances the endeavor is generally to find embodiments with which not only the particular objectives are achieved but other desired objectives need be lowered as little as possible. 
     The present invention also conforms to this latter pattern. Its object is to provide a novel type of titanium-containing catalyst component with which, given similar objectives, better results can be achieved than with conventional titanium-containing catalyst components, in particular in respect of the above categories (b) and (d). 
     We have found that this object is achieved with a titanium-containing catalyst component which is obtained by a special two-stage further treatment of the milled product (IV) obtained from the process defined at the outset. 
     Accordingly, the present invention relates to a process for the preparation of homopolymers and copolymers of C 2  -C 6  -α-monoolefins by polymerizing the monomer or monomers at from 30° to 200° C. under a pressure of from 0.1 to 200 bar, by means of a Ziegler catalyst system comprising 
     (1) a titanium-containing catalyst component and 
     (2) an aluminum compound of the formula 
     
         AlA.sub.3-n X.sub.n 
    
     where 
     A is a C 1  -C 18  -hydrocarbon radical, preferably a C 1  -C 12  -alkyl radical or C 3  -C 12  -alkenyl radical, and especially a C 2  -C 8  -alkyl radical, 
     X is chlorine, bromine or hydrogen, preferably chlorine or hydrogen and 
     n is from 0 to 2, preferably from 0 to 1, and especially 0, with the provisos that the atomic ratio of titanium from catalyst component (1) to aluminum from catalyst component (2) is from 1:0.1 to 1:500, preferably from 1:0.2 to 1:200, and that 
     (1.1) to prepare the catalyst component (1) 
     (1.1.1) a titanium compound (I) of the formula 
     
         TiCl.sub.3.z(AlCl.sub.3) or Cl.sub.m Ti(OB).sub.4-m 
    
     where z is from 0 to 0.5, especially from 0.31 to 0.35, m is from 0 to 3, especially from 0 to 2, and B is C 1  -C 18  -alkyl, especially C 2  -C 8  -alkyl, and 
     (1.1.2) a magnesium alcoholate (II) of the formula 
     
         Mg(OD).sub.2 
    
     where D is a monovalent C 1  -C 18  saturated-aliphatic and/or aromatic hydrocarbon radical, preferably a monovalent C 1  -C 10  saturated-aliphatic hydrocarbon radical or phenyl and especially C 1  -C 4  -alkyl, 
     (1.1.3) with or without, but advantageously with, a metal chloride (III) of the formula AlCl 3 , ZnCl 2  or MnCl 2 , preferably AlCl 3 , in the weight ratio of titanium compound (I) to magnesium alcoholate (II) of from 1:200 to 1:0.2, preferably from 1:1 to 1:100, and in the weight ratio of titanium compound (I) to metal chloride (III) of from 1:0 to 1:20, preferably from 1:0 to 1:5, are milled, preferably dry, with one another for from 1 to 200, preferably from 5 to 100, hours, under a milling acceleration of from 30 to 70 m/s 2 , to form a milled product ((IV), in which process, when preparing the catalyst component (1), 
     (1.2) in an additional stage 
     (1.2.1) the milled product (IV) obtained according to (1.1), 
     (1.2.2) a C 1  -C 12  -alkanol (V), preferably a C 1  -C 8  -alkanol (V) and 
     (1.2.3) a C 5  -C 12  -alkane (VI), preferably a C 6  -C 8  -alkane (VI) are brought together in the weight ratios of milled product (IV):alkanol (V)=from 1:0.01 to 1:1, preferably from 1:0.03 to 1:0.75, and milled product (IV):alkane (VI)=from 1:1 to 1:1,000, preferably from 1:1 to 1:100, to form a suspension (VII), and the batch is kept, with continuous mixing, at from 0° to 195° C., preferably from 10° to 100° C., for a period of from 0.5 to 60, preferably from 1 to 30, especially from 1 to 10, minutes, after which 
     (1.3) in a further additional stage 
     (1.3.1) there is added, to the suspension (VII) obtained according to (1.2), 
     (1.3.2) a metal compound (VIII) of the general formula 
     
         Mt G.sub.s-t E.sub.t 
    
     where 
     Mt is aluminum, silicon or titanium, preferably aluminum, 
     G is a C 1  -C 12  -hydrocarbon radical, preferably C 1  -C 12  -alkyl and especially C 2  -C 8  -alkyl, 
     E is chlorine, bromine, hydrogen or --OR, preferably chlorine or hydrogen, 
     R is a C 1  -C 12  -hydrocarbon radical, preferably C 1  -C 12  -alkyl, and especially C 2  -C 8  -alkyl, 
     s is the maximum valency of the metal Mt and 
     t is (a) from 0 to s-1, preferably from 1 to 2, if Mt is aluminum, (b) from 0 to 4, preferably from 1 to 4, if Mt is silicon, and (c) 4 if Mt is titanium, whilst maintaining a suspension state, addition being continued until the atomic ratio of magnesium from the solid contained in suspension (VII) to metal from the metal compound (VIII) is from 1:0.1 to 1:20, preferably from 1:1 to 1:10, the product (IX), which results from stage (1.3) and is present as a solid phase in the suspension, constituting the titanium-containing catalyst component (1). 
     The following details may be noted in respect of the process according to the invention: 
     The polymerization process as such can, taking into account the characterizing features, be carried out in virtually all relevant conventional technological embodiments, ie. as a batchwise, cyclic or continuous process, which may be, for example, a suspension polymerization, solution polymerization or dry phase polymerization process. The technological embodiments mentioned, ie. the technological embodiments of a Ziegler olefin polymerization, are well known from the literature and industrial practice and further details need not be given here. It may, however, be noted that the novel titanium-containing catalyst component (1) can, like corresponding prior art catalyst components, be brought together with catalyst component (2) outside or inside the polymerization vessel, in the last-mentioned case by, for example, spatially separate introduction of the components; component (1) may be handled in the form of a suspension and component (2) in the form of a solution. 
     Concerning the novel titanium-containing catalyst component (1), the following may be noted: 
     It is prepared in three stages referred to in the preceding and following text as (1.1), (1.2) and (1.3). 
     In stage (1.1), a titanium compound (I) of the type defined above and a magnesium alcoholate (II) of the type defined above, with or without, but advantageously with, a certain metal chloride are milled together, preferably dry, to form a milled product (IV). In stage (1.2), the latter is brought together with a certain alkanol (V) and a certain alkane (VI) and the mixture is treated to form a suspension (VII). In stage (1.3), a metal compound (VIII) of the type defined above is added to the last-mentioned suspension, so as to maintain a suspension state. The solid-phase product (IX) resulting from stage 1.3 and present in the suspension is the novel titanium-containing catalyst component (1). 
     As regards individual stages, the following may be noted: Stage (1.1) 
     The milling carried out in this stage exhibits no special features and can be carried out without problems by a skilled worker, without additional guidance. However, it may be mentioned that ball mills, in particular vibratory ball mills, are particularly suitable for the milling process. Stage (1.2) 
     Preparation of the suspension in this stage also entails no difficulties and is readily achieved by a skilled worker. However, it has proved advantageous first to suspend the milled product (IV) in the alkane (VI), by conventional methods, for example in a stirred vessel, and then to add the alcohol (V) to the resulting suspension at a rate such that local heat build-up is avoided. Stage (1.3) 
     This stage also presents no problems. It is merely necessary to bear in mind that the reaction taking place is exothermic and hence, again to avoid substantial local heat build-up, the metal compound (VIII) should not be introduced abruptly into the suspension (VII). 
     The novel titanium-containing catalyst component (1) which results from stage (1.3) in the form of a solid-phase product (IX) in suspension, can be used, as the titanium-containing catalyst component, directly in the form of the suspension obtained, with or without a prior wash by digestion with an alkane. In general, however, it is advantageous first to isolate the solid-phase product and then to employ it as the catalyst component (1). Isolation may be effected, for example, by separating the solid-phase product from the liquid phase by filtration, washing it with a pure alkane (for example of the type used as the suspending medium) and then drying, for example under reduced pressure. 
     The novel titanium-containing catalyst components (1), ie. the solid-phase products (IX), can be employed, in the initially defined polymerization process, in the same way as the titanium-containing compounds are conventionally employed in a Ziegler olefin polymerization. In this respect, the process according to the invention shows no special features, and reference may be made to the procedures which are well known from the literature and in industrial practice. It should merely be mentioned that the process is particularly suitable for the preparation of ethylene homopolymers and that where copolymers of ethylene with higher α-monoolefins, or homopolymers of higher α-monoolefins, are to be prepared, particularly suitable α-monoolefins are propene, but-1-ene, 4-methylpent-1-ene and hex-1-ene. The molecular weights of the polymers can be regulated in the relevant conventional manner, especially using hydrogen as the regulator. 
     As regards the materials concerned in the novel titanium-containing catalyst component (1), the following details may be noted: 
     The titanium compounds (I) to be employed in stage (1.1) can be the relevant conventional compounds conforming to the definition given, for example a titanium trichloride obtained by reducing titanium tetrachloride with hydrogen or with an aluminum trialkyl, a titanium trichloride/aluminum trichloride co-crystalline product of the formula TiCl 3 .1/3AlCl 3 , as obtained by reducing titanium tetrachloride with metallic aluminum, a tetraalkyl titanate or a reaction product of one of the above esters with not more than 3 moles, in particular not more than 1 mole, of titanium tetrachloride. The titanium compounds (I) may be employed in the form of individual compounds or of mixtures of two or more compounds. 
     The magnesium alcoholates (II) also to be employed in stage (1.1) may be derived, for example, from ethanol, n-propanol, i-propanol, n-butanol, sec.-butanol or tert.-butanol, or from phenol. Again, the alcoholates (II) may be employed in the form of individual compounds or of mixtures of two or more compounds. 
     The metal chlorides (III) which may or may not be employed additionally in stage (1.1) should be in a non-hydrated form. 
     C 1  -C 12  -Alkanols (V) are employed in stage (1.2). Specific examples are methanol, ethanol, the propanols, the butanols, n-hexanol, 2-ethylhexanol, n-octanol, n-decanol and 2,7-diethyloctanol. Examples of alcohols which have proved particularly suitable are methanol, ethanol, isopropanol and n-butanol. The alkanols (V) may be employed as individual compounds or as mixtures of two or more compounds. 
     C 5  -C 12  -alkanes (VI), eg. cyclopentane, cyclohexane, n-hexane, n-heptane, 2-ethylhexane, n-octane, n-decane or n-dodecane, are also employed in stage (1.2). Preferred alkanes are the hexanes, heptanes and octanes, as individual isomers or mixtures of isomers. n-Heptane is particularly suitable. Again, the alkanes (VI) may be employed as individual compounds or as mixtures of two or more compounds. The metal compounds (VIII) to be employed in stage (1.3) always contain the metal (Mt) in its highest valency, ie. trivalent aluminum, tetravalent silicon or tetravalent titanium. A suitable metal compound (VIII) is advantageously chosen from the following three categories of compounds: 
     Aluminum compounds represented by the formulae Al(C 2  H 5 ) 3 , Al(C 2  H 5 ) 2  Cl, Al(C 2  H 5 ) 2  Br, Al(C 2  H 5 ) 1 .5 Cl 1 .5, Al(C 2  H 5 ) 1 .5 Br 1 .5, Al(C 2  H 5 )Cl 2 , Al(C 2  H 5 )Br 2 , Al(C 4  H 9 ) 3 , Al(C 4  H 9 ) 2  Cl, Al(C 4  H 9 )Cl 2 , Al(C 2  H 5 ) 2  H, Al(C 4  H 9 ) 2  H, Al(C 3  H 7 ) 2  (OC 3  H 7 ) and Al(C 2  H 5 ) 1 .5 (OC 2  H 5 ) 1 .5, amongst which Al(C 2  H 5 ) 2  Cl, AL(C 2  H 5 ) 1 .5.Cl 1 .5, Al(C 2  H 5 )Cl 2  and Al(C 2  H 5 ) 2  H are particularly suitable. 
     Silicon compounds, as represented by the formulae SiCl 4 , SiBr 4 , Si(CH 3 ) 2  Cl 2 , Si(CH 3 ) 3  Cl, Si(C 2  H 5 ) 3  Cl, SiHCl 3 , Si(C 2  H 5 ) 3  H, Si(OC 2  H 5 ) 4  and Si(OC 6  H 5 ) 4 , amongst which SiCl 4 , Si(CH 3 ) 3  Cl, Si(C 2  H 5 ) 3  Cl and Si(C 2  H 5 ) 3  H are particularly suitable. 
     Titanium tetrachloride. 
     The metal compounds (VIII) may be employed in the form of individual compounds or of suitable mixtures of two or more compounds. 
     The relevant conventional compounds may be used as catalyst component (2); specific examples are Al(C 2  H 5 ) 3 , Al(i-C 4  H 9 ) 3 , Al(n-C 4  H 9 ) 3 , Al(C 8  H 17 ) 3  and isoprenylaluminum. 
     In conclusion, it is to be noted that the novel titanium-containing catalyst components (1) are sensitive to hydrolysis and to oxidation. Accordingly, when handling these substances, the conventional precautionary measures relevant to Ziegler catalysts (for example exclusion of moisture and use of an inert gas atmosphere) should be taken. 
    
    
     EXAMPLE 1 
     (a) Preparation of the Titanium-Containing Catalyst Component 
     First Stage 
     A titanium compound (I) of the formula TiCl 3 .0.33 AlCl 3  and magnesium phenolate (II) are milled dry with one another, in the weight ratio of 1:8, in a conventional ball mill, for 20 hours, under a milling acceleration of 50 m/s 2 , to give a milled product (IV). 
     Second Stage 
     1 part by weight of the milled product (IV) obtained from the first stage, 0.28 part by weight of ethanol (V) and 5 parts by weight of n-heptane (VI) are brought together by first suspending the milled product in the n-heptane and then adding the ethanol to the suspension in the course of 6 minutes. The batch (=suspension VII) is then kept at 50° C. for 20 minutes, with vigorous stirring. 
     Third Stage 
     Silicon tetrachloride is added slowly (over 15 minutes) to the suspension (VII) obtained from the second stage, at 25° C., whilst maintaining the suspension state, the addition being continued until the atomic ratio of magnesium from the solid contained in suspension (VII) to silicon is 1:1. 
     The solid-phase product which results from the third stage and is in suspension, ie. the desired titanium-containing catalyst component, is isolated by filtering off, washing with n-heptane and drying at 25° C. under reduced pressure; the titanium content is 2.88% by weight and the chlorine content 44.9% by weight. 
     (b) Polymerization By Means of the Titanium-Containing Catalyst Component 
     4,500 parts by weight of isobutane are introduced into a stirred autoclave which is half-filled; 0.1 part by weight of the novel catalyst component (in the form of a suspension in n-heptane, containing 15% by weight of solids) and 2.5 parts of weight of triethyl-aluminum are then added. Polymerization is then carried out for 2 hours whilst stirring and keeping the following parameters constant by a suitable regulating system: ethylene pressure=20 bar, hydrogen pressure (for regulating the molecular weight)=5 bar, temperature=100° C. The polymerization is then stopped by letting down the autoclave. 
     Details of the polymer obtained are to be found in the Table given later. 
     EXAMPLE 2 
     (a) Preparation of the Titanium-Containing Catalyst Component 
     First Stage 
     A titanium compound (I) of the formula TiCl 3 , magnesium ethylate (II) and aluminum chloride (III), in the weight ratio of titanium compound (I): magnesium compound (II)=1:3, and titanium compound (I):metal chloride (III)=1:1, are milled dry with one another, in a conventional ball mill, for 40 hours, under a milling acceleration of 50 m/s 2 , to give a milled product (IV). 
     Second Stage 
     1 part by weight of the milled product (IV) obtained from the first stage, 0.4 part by weight of n-butanol (V) and 2.7 parts by weight of cyclohexane (VI) are brought together by first suspending the milled product in the cyclohexane and then adding the n-butanol to the suspension in the course of 30 minutes. The batch (=suspension VII) is then kept at 50° C. for 15 minutes, with vigorous stirring. 
     Third Stage 
     Titanium tetrachloride is added slowly (over 10 minutes) to the suspension (VII) obtained from the second stage, at 25° C., whilst maintaining the suspension state, the addition being continued until the atomic ratio of magnesium from the solid contained in suspension (VII) to titanium is 1:1. Thereafter, the batch is stirred for a further 4 hours at 25° C. 
     The solid-phase product which results from the third state and is in suspension, ie. the desired titanium-containing catalyst component, is isolated by filtering off, washing with n-heptane and drying at 25° C. under reduced pressure; the titanium content is 8.41% by weight and the chlorine content 49.97% by weight. 
     (b) Polymerization By Means of the Titanium-Containing Catalyst Component 
     This is carried out under identical conditions to those described in Example 1, but using the catalyst component described above. 
     Details of the polymer obtained are again to be found in the Table given later. 
     EXAMPLE 3 
     (a) Preparation of the titanium-containing catalyst component 
     First Stage 
     A titanium compound (I) of the formula Cl 1  Ti(OB) 3 , where B is iso-butyl, magnesium n-butylate (II) and zinc chloride (III), in the weight ratio of titanium compound (I): magnesium compound (II)=1:2.3 and titanium compound (I): metal chloride (III)=1:1.4, are milled dry with one another, in a conventional ball mill, for 30 hours, under a milling acceleration of 55 m/s 2 , to give a milled product (IV). 
     Second Stage 
     1 part by weight of the milled product (IV) obtained from the first stage, 0.28 part by weight of ethanol (V) and 2.7 parts by weight of n-heptane (VI) are brought together by first suspending the milled product in the n-heptane and then adding the ethanol to the suspension in the course of 5 minutes. The batch (=suspension VII) is then kept at 45° C. for 15 minutes, with vigorous stirring. 
     Third Stage 
     Ethyl-aluminum dichloride is added slowly (over 15 minutes) to the suspension (VII) obtained from the second stage, at 25° C., whilst maintaining the suspension state, the addition being continued until the atomic ratio of magnesium from the solid contained in suspension (VII) to aluminum is 1:1.5. 
     The solid-phase product which results from the third stage and is in suspension, ie. the desired titanium-containing catalyst component, is isolated by filtering off, washing with n-heptane and drying at 25° C. under reduced pressure; the titanium content is 5.8% by weight and the chlorine content 38.45% by weight. 
     (b) Polymerization By Means of the Titanium-Containing Catalyst Component 
     This is carried out under identical conditions to those described in Example 1, but using the catalyst component described above. 
     Details of the polymer obtained are again to be found in the Table given later. 
     In the Table the symbols have the following meaning: 
     PE=Yield of polyethylene in parts by weight 
     PE/CC=Productivity in parts by weight of polyethylene per part by weight of the novel catalyst component 
     PE/Ti=Productivity in parts by weight of polyethylene per part by weight of titanium in the novel catalyst component 
     BW=Bulk density in g/l 
     MI=Melt index Mi 2 .16 190  (g/10 mins) 
     %&lt;0.1=Proportion of polyethylene particles, in % by weight, which have a particle diameter of less than 0.1 mm (fines). 
     
                       TABLE                                                       
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Example                                                                   
       PE     PE/CC     PE/Ti BW    MI   % &lt;0.1                           
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1      2600   26,000    903,000                                           
                              425   0.4  0.5                              
2      3680   36,800    437,600                                           
                              440   1.3  0.7                              
3      4750   47,500    819,000                                           
                              430   0.94 0.35                             
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