MX2008006628A - Olefin polymerization process - Google Patents

Abstract

A process for polymerizing an alpha-olefin is disclosed. The polymerization is performed in the presence of a catalyst system comprising a three-membered titanacycle. A wide variety of titanacycles can be readily prepared, making this a versatile and inexpensive olefin polymerization process.

Description

OLEFIN POLYMERIZATION PROCESS Field of the invention The invention relates to a process useful for the polymerization of olefins. The process uses a catalyst system that incorporates a cyclic titanium complex. BACKGROUND OF THE INVENTION Interest in catalysis continues to increase in the polyolefin industry. Many catalysts are known for the polymerization of olefin, including conventional Ziegler-Natta catalysts. To improve polymer properties, single-site catalysts, in particular metallocenes, are beginning to replace the Ziegler-Natta catalysts. Single-site catalysts commonly require large amounts of expensive activators such as methylalumoxane or salts of non-nucleophilic anions, such as triphenylcarbenium tetracis (pentafluorophenyl) borate. Many single-site catalysts are difficult to synthesize. This increases the cost of the catalyst system. It would be desirable to incorporate the advantages of single-site catalysts, such as narrow molecular weight distribution and good comonomer incorporation, without the high cost. Single-site catalysts commonly incorporate at least one stable anionic ligand in polymerization that is purely aromatic, such as in a cyclopentadienyl system. All five carbons in the cyclopentadienyl ring participate in the? -5 bond to the metal. The cyclopentadienyl anion functions as a 6tt electron donor. Apparently, a similar linkage occurs with heteroatomic ligands such as borate benzene or azaborolinyl. U.S. Patent Nos. 5,459, 1 1 6, 5, 798,424, and 6,114,276 present catalysts for olefin polymerization that do not require the use of expensive activators. U.S. Patent No. 5,459,116 uses titanium compounds which are reacted with hydroxyesters such as 2-hydroxyethyl methacrylate. U.S. Patent No. 6,111,2766 reacts titanium compounds with carbodiimide ligands and U.S. Patent No. 5,798,424 prepares five-membered chelated titanium compounds. Similarly, European Patent No. 1, 238,989 and US Patent No. 6,897,176 do not require the use of expensive activators, and use five- or six-member chelated compounds. Other transition metal complexes containing chelating ligands are known. U.S. Patent No. 5,637,660 discloses transition metal complexes containing chelating ligands based on pyridine or quinoline. Science and Technology in Cataivsis (2002) 51 7 describes transition metal complexes based on phenoxymethides supported on magnesium chloride. None of these are three-membered titanium cyclic complexes.

Single-site transition metal complexes based on amine derivatives such as alkoxyamines are known for olefin polymerizations (see, for example, U.S. Patent Nos. 6,204.21 6 and 6, 281, 308, Oraanometallics 23 (2004) 836, Orqanometallics 23 (2004) 1 405, and Chem. Commun. 1 6 (2005) 21 52). The nitrogen atom is attached to a heteroatom and has two additional substituents. While the electron pair alone at the nitrogen atom coordinates with the transition metal, nitrogen is not formally bound to the metal and a three-membered titanium cyclic complex is not used. In the example given, the Group 4 element, zirconium, is bonded to 4 atoms including the oxygen atom of the monoanionic ligand (prepared from n-butyllithium and N, N-diethylhydroxylamine). The nitrogen atom is not one of the four atoms formally bound to zirconium. Three-membered titanium cyclic complexes have been made by reacting Ti (II) species with pi bonds (see, for example, J. Organometal, Chem. 624 (2001) 229, Orqanometallics 22 (2003) 24, and Eur. J Orq Chem. (2003) 4721). For example, the titanium diisopropoxide can be reacted with ketones or nitriles to give the corresponding three-membered titanium cyclic complexes. While three-membered titanium cyclic complexes are known, apparently the olefin polymerization processes using catalyst systems incorporating a three-membered titanium cyclic complex have not been contemplated. This type of polymerization process has many advantages in terms of ease of preparation of a wide variety of catalyst systems. BRIEF DESCRIPTION OF THE INVENTION The invention is a polymerization process. An alpha-olefin is polymerized in the presence of a catalyst system containing a three-membered titanium cyclic complex. A wide variety of cyclic titanium complexes can be easily prepared from inexpensive raw materials. The process is versatile and incorporates many of the advantages of known processes with catalyst in a single site without the high cost associated with complex catalyst systems. DETAILED DESCRIPTION OF THE INVENTION The invention is a process for polymerizing an alpha-olefin in the presence of a three-membered titanium cyclic complex. One of the three atoms that make up the three-membered ring is titanium. The second atom is oxygen or nitrogen. When the second atom is oxygen, the third atom is carbon, sulfur, or phosphorus. When the second atom is oxygen, the cyclic titanium complex preferably has the general formula: wherein Q is selected from the group consisting of C, S, and P; each R is independently selected from the group consisting of hydrocarbyl and if from 1 to 20 carbon atoms; when Q is C or S, n is 2; when Q is P, n is 3; and each X is independently selected from the group consisting of halide, alkoxy, siloxy, alkylamino, and hydrocarbyl of 1 to 30 carbon atoms. The cyclic titanium complex can be conveniently made from a divalent titanium compound and the corresponding aldehyde, ketone, sulfoxide, or phosphine oxide by the following scheme, wherein X, Q, R, and n are as previously defined .

When the solution is stored, the cyclic titanium complexes can be dimerized. Preferably, X provides steric bulk because this decreases the tendency to dimerization. For example, when X is isopropoxide, the stability improves with respect to when X is chloride. Examples of structures when the second atom is oxygen: When the second atom is nitrogen, the nitrogen atom is unsubstituted or mono substituted. When the second atom is unsubstituted nitrogen, the third atom is carbon and the cyclic titanium complex preferably has the general formula: where X and R are as previously defined. These cyclic titanium complexes can be easily prepared from a divalent titanium compound and the corresponding nitrile. When the second atom is substituted mono nitrogen, the third atom is nitrogen, oxygen, or carbon and the cyclic titanium complex preferably has the general formula: wherein Z is selected from the group consisting of oxygen, substituted mono-N, and disubstituted C; X and R are as previously defined. The cyclic titanium complex can be conveniently made from a divalent titanium compound and the corresponding imine, azo compound or nitrone by the following scheme, wherein X, Z, and R are as previously defined.

In the storage of the solution, cyclic titanium complexes can be dimerized. Preferably, X provides steric bulk because this decreases the tendency to dimerization. For example, when X is isopropoxide, the stability improves with respect to when X is chloride. Examples of structures in which the second atom is nitrogen: Preferably, the catalyst system further includes an aluminum compound. Suitable aluminum compounds include alumoxanes such as methyl alumoxane (MAO), polymeric MAO (PMAO), and ethyl alumoxane, alkyl aluminum halides such as ethyl aluminum dichloride, alkyl aluminum dihalides such as diethyl aluminum chloride, and trialkyl aluminum such as trimethylaluminum, triisobutylaluminum, and triethylaluminum. When an aluminum alkyl compound is used, preferably it is an alkyl aluminum halide, an alkyl aluminum halide or a trialkyl aluminum. More preferably it is a trialkyl aluminum. The optimum amount of aluminum compound relative to the amount of other catalyst components depends on many factors, including the nature of the cyclic complex of titanium and aluminum compound, the purity of the solvent, the speed of the desired reaction, the conditions of the reaction, and other factors. Generally, however, the amount used will be within the range of from about 0.01 to about 1000 moles, preferably from about 0.1 to about 50 moles, and more preferably from about 1 to about 5 moles, of aluminum per mole of titanium metal. The aluminum compound can be combined with the cyclic titanium complex and added to the reactor as a mixture, or the components can be added to the reactor separately. Preferably, the catalyst system includes a support. The support is preferably a porous material such as oxides and inorganic chlorides, and organic polymer resins. Preferred inorganic oxides include oxides of the elements of groups 2, 3, 4, 5, 1 3, or 1 4. Preferred supports include silica, alumina, silica-aluminas, magnesiums, titaniums, zirconiums, magnesium chloride, and cross-linked polystyrene. More preferably, the support is silica or magnesium chloride. The amount of titanium cyclic complex added per g of support material is preferably from 0.01 mmol per gram to 0.8 mmol per gram. When the silica is the support, preferably the silica has a surface area in the range from about 10 to about 1000 m2 / g, more preferably from about 50 to about 800 m2 / g, and most preferably from about 200 to about approximately 700 m2 / g. Preferably, the pore volume of the silica is in the range of from about 0.05 to about 4.0 mL / g, more preferably from about 0.08 to about 3.5 mL / g, and most preferably from about 0.5 to about 3.0 mL / g. Preferably, the average particle size of the silica is in the range from about 1 to about 500 μm, more preferably from about 2 to about 200 μm, and most preferably from about 5 to about 1 00 μm. The average pore diameter is commonly in the range from about 5 to about 1000 angstroms, preferably about 10 to about 500 angstroms, and much more preferably about 20 to about 350 angstroms. Preferably, the silica is dried before use. Preferably, drying is carried out at a temperature from about 1000 ° C to about 800 ° C, more preferably from about 150 ° C to about 600 ° C. A variety of different chemical support treatments can be used, including reaction with organoaluminum, magnesium, silicon, or boron compounds. See, for example, the techniques described in US Pat. No. 6,21 1, 31 1. The aluminum compound can be added directly to the polymerization reactor before or after adding the cyclic titanium complex. In other words, a supported titanium cyclic complex can be prepared first without the aluminum compound. In a preferred process, a solution of the cyclic titanium complex is combined with the support. The mixture is stirred in an inert atmosphere at a temperature from about 0 ° C to about 1 20 ° C, more preferably from about 20 ° C to about 40 ° C. The optimum agitation time will vary somewhat, depending on the amounts of solvent and support, but it will be long enough to ensure good mixing. Preferably, the stirring time is from about 2 minutes to about 60 minutes. Shaking for more than 60 minutes will not decrease activity, but it is unnecessary. Shaking for 30 minutes at room temperature is convenient and gives good results. If a large amount of solvent is used, the mixture is a suspension and it is convenient to remove some of the solvent to prepare a free flowing solid. This can be done at room temperature by applying a vacuum. In a preferred embodiment, an incipient wetting technique is used. A small amount of solvent is used to dissolve the cyclic titanium complex and the solution is added to the support. The mixture continues to be a solid that flows freely without removal of the solvent. The mixture can be used as is or the residual solvent can be removed. In another preferred embodiment, a solution of the aluminum compound is added to the support before the addition of the cyclic titanium complex. This solution may contain all the aluminum compound to be used, but preferably, contains a part of the aluminum compound to be used. Any remaining aluminum compound can be premixed with the cyclic titanium complex or can be added to the reactor at the start of the polymerization. Even more preferably, the cyclic titanium complex is pre-mixed with a solution of part or all of the aluminum compound before addition to the support. Preferably, the cyclic titanium complex and the aluminum compound solution are pre-mixed for a period of time between 1 minute and two hours. When the cyclic titanium complex is previously mixed with a solution of the aluminum compound, it is preferable to use a part of the aluminum compound and to add the rest of the aluminum compound either to the support before the addition of the premix or directly to the reactor. Preferably, a purifying amount of alkylaluminum compound such as triethylaluminum or triisobutylaluminum is also added to the reactor. Preferably, the alkylaluminium compound is added to the reactor before the addition of the cyclic titanium complex. The invention is an alpha-olefin polymerization process.

By "polymerizing an alpha-olefin," it is meant to include homopolymerizations, as well as copolymerizations. The copolymers can be block, random or alternative copolymers. Preferred alpha-olefins are ethylene, propylene, 1-butene, 1-hexene, 1-ketene, and mixtures thereof. Most preferred are ethylene and combinations of ethylene with a second olefin. Optionally, hydrogen is used in the polymerization processes of the invention to regulate the molecular weight of the polyolefin. The amount of hydrogen needed depends on the molecular weight of the polyolefin and the desired melt flow properties. Generally, as the amount of hydrogen increases, the molecular weight of the polyolefin decreases and the melt index increases. For many applications, the melt index of the polyolefin will be too low if the polymerization is carried out in the absence of hydrogen. The process provides good control of molecular weight and melt flow properties by using small amounts of hydrogen. The polymerizations are usually carried out under pressure. The pressure is preferably in the range from about 0.5 M Pa to about 35 M Pa, more preferably from about 5 MPa to about 25 M Pa. Many types of polymerization processes can be used. The process can be carried out in the gaseous phase, in volume, solution or suspension. The polymerization can be carried out over a wide range of temperatures. Generally, lower temperatures produce higher molecular weight and longer catalyst times. However, because the polymerization is exothermic, it is more difficult to achieve lower temperatures. A balance must be made between these two factors. Preferably, the temperature is within the range from about 0 ° C to about 150 ° C. A more preferred range is from about 20 ° C to about 90 ° C. The concentrations of cyclic titanium complex used for olefin polymerizations depend on many factors. Preferably, however, the concentration ranges from about 0.01 micro-moles per liter to about 1 00 micro moles per liter. The polymerization times depend on the type of process, the concentration of catalyst and other factors. Generally, polymerizations are complete in the range from several seconds to several hours. The following examples merely illustrate the invention. Those skilled in the art will recognize many variations that are within the spirit of the invention and the scope of the claims. Example 1 Polymerization with titanium cyclic complex io 1 A solution of titanium tetraisopropoxide (20 mmol) in anhydrous, deoxygenated tetrahydrofuran (40 mL) is cooled to -78 ° C and 25 mL of 1.6 M n-butyllithium in hexane is slowly added. The reaction mixture is stirred for one hour at -78 ° C, the cooling bath is removed, and the mixture is stirred at room temperature for 1 8 hours. Vacuum is applied to eliminate volatile substances. The expected solid product is a mixture of titanium diisopropoxide and lithium isopropoxide. Anhydrous deoxygenated tetrahydrofuran (20 mL) is added to the solid. Benzophenone (20 mmol) is added to the solution under stirring and the reaction is heated at reflux for 1 8 hours. Vacuum is applied to eliminate volatile substances. The expected solid product is a mixture of cyclic complex of titanium 1 and lithium isopropoxide which is used "as is" in the following polymerization. To a 1 L stainless steel autoclave reactor, 85 mL of 1 -hexene is added. Then triisobutylaluminum (1.0 mL of 1.0 M solution in heptane, 1.0 mmol) is run in the reactor under nitrogen and isobutane pressure (approximately 400 mL), and the reactor is pressurized with ethylene to 2.4 MPa. The content of the reactor is allowed to equilibrate at 80 ° C. In a separate container, 0.5 g of anhydrous magnesium chloride is suspended in 4 mL of toluene. Cyclic titanium complex 1 (2.0 mmol) is added, and the mixture is heated with stirring for two hours at 80 ° C. The mixture is cooled to room temperature, loaded onto an injector arm in a glove box, and then run in the reactor with isobutane (1 00 mL) and nitrogen pressure. The polymerization is carried out at 80 ° C for 30 minutes, and then the reactor is vented. A copolymer of ethylene-hexene is the expected product. Example 2. Polymerization with titanium cyclic complex 2 A solution of titanium tetraisopropoxide (20 mmol) in anhydrous, deoxygenated tetrahydrofuran (40 mL) is cooled to -78 ° C and 25 mL of 1.6 M n-butyllithium in hexane is added slowly.

The reaction mixture is stirred for one hour at -78 ° C, the cooling bath is removed, and the mixture is stirred at room temperature for 1 8 hours. Vacuum is applied to eliminate volatile substances. The expected solid product is a mixture of titanium diisopropoxide and lithium isopropoxide. Anhydrous deoxygenated tetrahydrofuran (20 mL) is added to the solid. Azobenzene (20 mmol) is added to the solution under stirring and the reaction is heated at reflux for 1 8 hours. Vacuum is applied to eliminate volatile substances. The expected solid product is a mixture of cyclic complex of titanium 2 and lithium isopropoxide which is used "as is" in the following polymerization. To a 1 L stainless steel autoclave reactor, 85 mL of 1 -hexene is added. Then triisobutylaluminum (1.0 mL of 1.0 M solution in heptane, 1.0 mmol) is run in the reactor under nitrogen and isobutane pressure (approximately 400 mL), and the reactor is pressurized with ethylene to 2.4 MPa. The content of the reactor is allowed to equilibrate at 80 ° C. In a separate vessel, 0.5 g of anhydrous magnesium chloride is suspended in 4 mL of toluene. Cyclic titanium complex 2 (2.0 mmol) is added, and the mixture is heated with stirring for two hours at 80 ° C. The mixture is cooled to room temperature, loaded into an injector arm in a glove box, and then run in the reactor with isobutane (1 00 mL) and nitrogen pressure. The polymerization occurs at 80 ° C for 30 minutes, and then the reactor is vented. A copolymer of ethylene-hexene is the expected product.

Example 3 Polymerization with cyclic titanium io 3 complex A solution of titanium tetraisopropoxide (20 mmol) in anhydrous, deoxygenated tetrahydrofuran (40 mL) is cooled to -78 ° C and 25 mL of 1.6 M n-butyllithium in hexane is added slowly. The reaction mixture is stirred for one hour at -78 ° C, the cooling bath is removed, and the mixture is stirred at room temperature for 1 8 hours. Vacuum is applied to eliminate volatile substances. The expected solid product is a mixture of titanium diisopropoxide and lithium isopropoxide. Anhydrous deoxygenated tetrahydrofuran (20 mL) is added to the solid. Benzonitrile (20 mmol) is added to the solution under stirring and the reaction is heated at reflux for 18 hours. Vacuum is applied to eliminate volatile substances. The expected solid product is a mixture of cyclic complex of titanium 3 and lithium isopropoxide which is used "as is" in the following polymerization. To a 1 L stainless steel autoclave reactor, 85 mL of 1 -hexene is added. Then triisobutylaluminum (1.0 mL of 1.0 M solution in heptane, 1.0 mmol) is run in the reactor under nitrogen and isobutane pressure (approximately 400 mL), and the reactor is pressurized with ethylene to 2.4 MPa. The content of the reactor is allowed to equilibrate at 80 ° C. In a separate vessel, 0.5 g of anhydrous magnesium chloride is suspended in 4 mL of toluene. The cyclic titanium complex 3 (2.0 mmol) is added, and the mixture is heated with stirring for two hours at 80 ° C. The mixture is cooled to room temperature, loaded into an injector arm in a glove box, and then run in the reactor with isobutane (1 00 mL) and nitrogen pressure. The polymerization is carried out at 80 ° C for 30 minutes, and then the reactor is vented. An ethylene-hexene copolymer is the expected product. The preceding examples are for illustrative purposes only. The following claims define the invention.

Claims (14)

REVIVAL DICTION EN

1 . A process comprising polymerizing an alpha-olefin in the presence of a catalyst system containing a three-membered titanium cyclic complex, characterized in that the remaining two atoms forming the cyclic titanium complex are selected from the group consisting of: combination with carbon, sulfur, or phosphorus; mono substituted nitrogen in combination with nitrogen, oxygen, or carbon; and unsubstituted nitrogen in combination with carbon.

2. The process of claim 1 further characterized in that the alpha-olefin is selected from the group consisting of ethylene, propylene, 1-butene, 1-hexene, 1-ketene, and mixtures thereof.

3. The process of claim 1, further characterized in that the catalyst system further includes an aluminum compound selected from the group consisting of alkylaluminum halides, alkylaluminum dihalides, and trialkylaluminums. 4. The process of claim 3, further characterized in that the aluminum compound is a trialkylaluminum selected from the group consisting of triethylaluminum, triisobutylaluminum, and trimethylaluminum. 5. The process of claim 1, further characterized in that the cyclic titanium complex has the general formula: wherein R is selected from the group consisting of oxygen, hydrocarbyl and silyl of 1 to 20 carbon atoms; and each X is independently selected from the group consisting of halide, alkoxy, siloxy, alkylaminium and hydrocarbyl of 1 to 30 carbon atoms. 6. The process of claim 1, further characterized in that the cyclic titanium complex has the general formula: wherein Q is selected from the group consisting of C, S, and P; each R is independently selected from the group consisting of hydrocarbyl and silyl of 1 to 20 carbon atoms; when Q is C or S, n is 2; when Q is P, n is 3; and each X is independently selected from the group consisting of halide, alkoxy, siloxy, alkylamino, and hydrocarbyl of 1 to 30 carbon atoms. The process of claim 1, further characterized in that the catalyst system further includes a support. The process of claim 8, further characterized in that the support is selected from the group consisting of silica, alumina, magnesium chloride, and mixtures thereof. 9. The process of claim 7, further characterized in that the support is magnesium chloride deposited on silica. 1. The process of claim 1, further characterized in that the polymerization is carried out at a temperature in the range from about 30 ° C to about 100 ° C. eleven . A suspension polymerization process of claim 1. 1 2. A gaseous phase polymerization process of claim 1. 1 3. A process comprising polymerizing an alpha-olefin in the presence of a catalyst system comprising a cyclic three-membered titanium complex having the general formula: wherein Z is selected from the group consisting of oxygen, substituted mono-N, and disubstituted C; R is selected from the group consisting of hydrocarbyl and silyl of 1 to 20 carbon atoms; and each X is independently selected from the group consisting of halide, alkoxy, siloxy, alkylamino, and hydrocarbyl of 1 to 30 carbon atoms.

14. The process of claim 13, further characterized in that the alpha-olefin is selected from the group consisting of ethylene, propylene, 1-butene, 1 -hexene, 1-ketene and mixtures thereof.

5. The process of claim 13, further characterized in that the catalyst system further comprises an aluminum compound selected from the group consisting of alkylaluminum halides, dialkylaluminum halides and trialkylaluminums. 1

6. The process of claim 1, further characterized in that the aluminum compound is a trialkylaluminum selected from the group consisting of triethylaluminum, triisobutylaluminum and trimethylaluminum. 1

7. The process of claim 1 3, further characterized in that the catalyst system further comprises a support. The process of claim 1 7, further characterized in that the support is selected from the group consisting of silica, alumina, magnesium chloride, and mixtures thereof. 9. The process of claim 13, further characterized in that the polymerization is carried out at a temperature in the range from about 30 ° C to about 1000 ° C.