PROCESS FOR THE PREPARATION OF ETHYLENE-PROPYLENE-DIENE TERPOLYMERS

Abstract: Ethylene-propylene-diene terpolymers are prepared by the polymerization of mixtures of the three monomers, carried out in the presence of catalysts comprising: A) A solid catalytic component containing at least on its surface compounds or mixtures of compounds comprising Mg, Ti, halogens and an electron-donor compound, char­ acterized in that at least 50% by weight of Ti com­ pounds present in it are insoluble in Ti tetrachloride at 80°C, and that the surface area after extraction by TiCl₄ is greater than 40 m²/g, and B) an organometallic compound of aluminium. In particular, the component A) comprises a titanium tetrahalide and an electron-donor compound, supported on anhydrous MgCl₂ or MgBr₂ in active form, the X-ray dif­ fraction spectrum of which shows, in lieu of the highest­ intensity line appearing in the normal dihalide spectrum, a halo having an intensity maximum shifted relatively to the d distance of such line.

Description: Background of the Invention 1. Field of the Invention The present invention relates to a process for the preparation of vulcanizable elastomeric copolymers of ethylene with propylene and one or more diene(s). More precisely, it relates to a process for the copolymerization of ethylene with propylene and butadiene and to elastomeric terpolymers obtained thereby,having low values of tension set at low temperatures. 2. Description of the Prior Art The elastomeric terpolymers, containing butadiene in lieu of a non-conjugated diene, for example 5-ethylidene-­ 2-norbornene or 1,4-hexadiene (commonly used) are greatly interesting, because of the low cost of their monomers, and of the simplifying in the preparation process allowed by the fact that all the monomers used are in the gas phase, and hence can be easily removed at the end of the polymerization. The copolymerization of ethylene and of alpha-ole­ fins either in the presence or in the absence of diole­ fins has been carried out by using different types of catalysts: one of the most widely used is constituted by the product from the reaction of a vanadium compound and an organometallic derivative of the metals of Groups I,II and III of the Periodic System (GB 1,277,629; IT 890,604; GB 1,277,353; IT 879,026; GB 1,519,472). The copolymers obtained by this catalyst are comple­ tely or substantially amorphous, and are obtained with rather low yields (grams of polymer per gram of vana­ dium). Catalysts having a much higher catalytic activity than the above said catalysts have already been claimed by the present Applicant in some prior patents. In USP 3,789,036, e.g., a process is disclosed for the preparation of elastomeric terpolymers, which can be vulcanized with sulphur, of ethylene with propylene and with either conjugated or non-conjugated diene monomers, by using a catalyst obtained by mixing an Al-alkyl or an Al-alkyl hydride with the product from the reaction of a titanium compound with a support constituted by an anhy­ drous magnesium halide in active form. However, neither the yields obtained nor the quality of the product are yet satisfactory. In USP 4,013,823 a process is disclosed for the preparation of saturated ethylene/propylene elastomers by copolymerization of the ronomers in the presence of cata­ lysts formed by a mixture of an Al-alkyl with a titanium halide, this latter being supported on a complex of an anhydrous magnesium halide with a Lewis base(electron donor). Such a catalyst is however not suitable for use in the preparation of terpolymers of ethylene and propyl­ ene with a conjugated diolefin. The yields and the elas­ tomeric properties of the terpolymer are indeed poor. From Belgian patent No. 848,527 catalysts are more­ over known, which are obtained by contacting the follow­ ing components: a) a solid product containing at least on its surface compounds or mixtures of compounds comprising Mg, Ti, halogens and an electron-donor compound, such product being chararacterized in that at least 50% by weight of Ti compounds present in it are insoluble in Ti tetrachloride at 80°C; b) an organometallic compound of Al, in the form of a complex with an electron-donor compound. Such catalysts make it possible, according to the above mentioned patent, propylene or propylene with small amounts of ethylene to be polymerized with very high yield, and propylene homopolymers or crystalline satu­ rated copolymers of propylene and ethylene to be obtained with extremely high yield. The Present Invention It has been now surprisingly found,and that is the object of the present invention,that by using catalysts obtained by contacting the above described solid product with an organometallic compound of Al, unsaturated elasto­ meric copolymers of improved quality can be obtained with very high yield, by polymerizing ethylene with propylene and one or more diene(s). It has been found in particu­ lar that very good results are achieved also when using conjugated dienes, which, as it is well known, are diffi­ cult to be polymerized by the Ziegler-Natta catalysts. Thanks to the high yield of these catalysts, the preparation becomes possible of the said copolymers by simplified methods, which do not comprise steps of puri­ fication from the catalyst residues. In particular, the catalysts used in the present invention comprise the products obtained by contacting the following components: A) a solid product containing at least on its surface compounds or mixtures of compounds comprising Mg, Ti, halogens and an electron-donor compound, the electron-­ donor compound moles/ Ti ratio being greater than 1, the halogen atoms /Ti ratio being greater then 4; such component being furthermore chararacterized in that at least 50% by weight of Ti compounds present in it are insoluble in Ti tetrachloride at 80°C, and that the surface area after extraction by TiCl₄ is greater than 40 m²/g. B) an organometallic compound of aluminium selected among Al-trialkyls, Al-alkyl hydrides and Al-alkyl monohal­ ides. Preferably, the component A) of the invention com­ prises at least on its surface products obtained from the reaction of Mg halides, selected between Mg dichlor­ ide and Mg dibromide, and halogenated compounds of tetra­ valent Ti, in particular TiCl₄, Tibr₄, Ti halo-alkoxides, with an electron-donor compound, selected from the esters of aromatic acids, such as, e.g., benzoic acid, and the aromatic nitriles, such as, e.g., benzonitrile. The na­ ture and composition of this component are furthermore defined by the following parameters. The Mg/Ti atomic ratio is comprised within the range of from 3 to 40 and preferably of from 10 to 30; the halogen atoms/Ti ratio is comprised within the range of from 10 to 90 and preferably of from 20 to 80, and the electron-donor compound moles/Ti ratio is comprised with­ in the range of from 1 to 6 and preferably of from 1.2 to 3. Particularly suitable components A) are furthermore characterized in that the highest-intensity line appear­ ing in the spectrum of Mg chloride or bromide of normal type, as defined in ASTM 3-0854 and 15-836 cards for the chloride and bromide respectively, has decreased in relative intensity and has an unsymmetrically broadened shape, forming a halo showing an intensity peak shifted relatively to the interplanar distance d of the highest-­ intensity line, or the spectrum is characterized in that such highest-intensity line is not any longer present, and instead of it a halo with an intensity peak shifted relatively to the'distance d of said line is present. In case of MgCl₂, the intensity peak of the halo is 10 comprised between d = 2.44 and 2.97 Å. In case of MgBr₂, the intensity peak of the halo is comprised between 2.80 and 3.24 Å. Component A) can be prepared according to various routes. A general method consists in treating by a liquid Ti compound a composition comprising a Mg halide and a complex formed by said Mg halide and an electron-donor compound, wherein the Mg/moles of electron-donor compound ratio in greater than 2 a d is preferably comprised within the range of from 2 to 15, under such conditions that on said composition the fixing occurs of a certain amount of Ti compounds, and in subsequently separating the solid reaction product from the liquid phase, under conditions under which on the product practically no Ti compounds soluble in boiling n-heptane and extractable by Ti tetrachloride at 80°C may remain. Another method consists in reacting an adduct of Mg halide and an alcohol, with an Al-alkyl, and in subse­ quently treating the reaction product with an excess of TiCl₄ at temperatures ranging from 60°C to TiCl₄ boiling point. Al-alkyl compound is used in such case in a ratio to the adduct at least sufficient to react with all the alcohol present. A further method consists in co-grinding the Mg halide, the titanium compound and the electron-donor compound under such conditions as to reduce the size of Mg halide crystallites to average values comprised within the range of from 40 to 100 Å, and in subsequently treating the so-obtained powder with an aliphatic or aromatic organic solvent selected among the liquids having dielectric constant at 20°C greater than or equal to 2. The preferred conditions for the treatment of the co-ground solid by the liquid mentioned are the follow­ ing: temperatures comprised between 10 and 150°C; times comprised between 0.5 and 10 hours, Mg halide/organic liquid ratio ranging from 5:1 to 1:12 by weight. Finally, the solid is washed with an aliphatic hydrocarbon to remove the soluble Ti compounds and is dried. The Al organometallic compounds which can be used as component B) are preferably constituted by Al-trialkyl compounds, such as for example trietilaluminium, tri-n­ propylaluminium, triisobutylaluminium, Al(C₁₂H₂₅)₃, by Al-alkyl hydrides, such as Al-diethyl hydride or Al-alkyl monohalides, such as diethyla­ luminium chloride, or mixtures thereof. The copolymerization of ethylene with propylene and the diene by using the catalyst defined hereinabove is carried out by operating in the presence or in the ab­ sence of an inert hydrocarbon diluent,such as, e.g., n-­ propane, n-butane, n-hexane,n-heptane, n-decane, ben­ zene,toluene, in the presence of a mixture of the cata­ lyst components A) and B). In such a mixture, the ratio between such components does not seem crytical; molar Al/Ti.ratios greater than 1 and preferably greater than 50 are preferably used. The polymerization temperature is generally main­ tained between -20 and 150°C, and preferably between 20 and 90°C. The operating pressure is a function of the temperature and of the reacting mixture, and can be the atmospheric or a superatmospheric pressure. The diolefins which can be polymerized with ethylene and propylene by the process of the present invention can 15be conjugated diolefins (1,3-butadiene,isoprene, piper­ ylene,monocyclopentadiene, etc.), or non-conjugated diolefins(5-ethylidene-2-norbornene,hexadiene-1,4, etc.). They are preferably conjugated diolefins,and particularly 1,3-butadiene. Propylene, ethylene and the diene are preferably polymerized with each other in such ratios as to obtain copolymers containing from 30 to 60% by weight of pro­ pylene and a diene amount not greater than 10% by weight. The following Examples are reported to the purpose of better illustrating the invention without it being limited to them. Preparation of ethylene-propylene-diene terpolymers Into a 1500-ml steel autoclave, equipped with mag­ netic stirrer, jacket and temperature control means, propylene and the diene are charged, after purging by nitrogen. The temperature is increased to the prefixed value, and ethylene under the desired pressure is intro­ duced up to saturation. The catalytic system is prepared separately,by placing in contact the solid catalytic component A) and component B) under nitrogen for 5 minutes at room tempe­ rature. The suspension obtained is injected into the auto­ clave through an ethylene-pressurized small bomb. The test is carried out by keeping constant the temperature (automatically) and the pressure (by feeding ethylene). When the use of H₂ as molecular weight regulator is required, this is introduced into the reactor before the saturation by ethylene. At the end of the test, 10 ml of acetone, containing IRGANOX 1010 in the ratio 0.3/100 to the polymer pro­ duced, is introduced. After 5 minutes the monomers are vented off and the autoclave is opened. The polymer is recovered and dried under nitrogen stream at 70°C. Preparation of Catalytic Component "A1" Into a stainless-steel container of cylindrical shape, having an inner volume of 1 litre, provided with outer jacket, containing 210 steel balls of 16 mm in diameter, by operating under a dry nitrogen atmosphere, 44,2 g of anhydrous MgCl₂ (H₂O 1% by weight) (equal to 0.46 mol) and 24.3 g of ethyl benzoate (equal to 0.162 mol) are introduced. After tightly sealing the container, the grinding is carried out by means of a mill of "Vibratom" type market­ ed by Siebtechnik, adjusted to operate at 1500 oscilla­ tions per minute, with total amplitude of 35 mm. The temperature is kept controlled at 18°C by circulating water through the jacket. After a 30 hours grinding, into the container, al­ ways operating under nitrogen atmosphere, 30.73 g of TiCl₄ (equal to 0.162 mol) is introduced. The grinding is started again, under the same condi­ tions, and is continued over more than 20 hours. The powdered product recovered after the discharging has the following composition by weight: Mg = 11.05%; Ti = 7.95%; Ethyl benzoate = 20.5%. Preparation of Catalytic Component "A2" By the same equipment as used for the preparation of the catalytic component "A1", 72.5 g of anhydrous MgCl₂ (equal to 0.76 mol) and 26.2 g of ethyl benzoate (equal to 0.174 mol) are ground together for 50 hours at 70°C. Twenty grams of the so-obtained powder is submitted to two titanation treatments, each by 285 ml of TiCl₄ at 80°C for 2 hours. This operation is carried out in a 500-­ ml glass flask, provided with jacket, filter plate and valve for bottom-discharging, reflux condenser and stir­ rer, with nitrogen-filled plenum chamber. After the processing at 80°C, the liquid phase is separated by filtering through the filter plate, and the solid is washed five times with 100-ml portions of hexane at 50oC, and is then dried in vacuo (under a residual pressure of about 3 mm Hg ) at 40°C for 3 hours. The analytical composition by weight of the product is the following: Mg = 19.9%; Ti = 1.5%; Ethyl benzoate = 10.2%. Preparation of the Catalytic Component "A3" By using the same equipment as described for the preparation of catalytic component "A1", 70 g ofanhy­ drous MgCl₂ (equal to 0.734 mol) and 30 g of ethyl ben­ zoate (equal to 0.2 mol) are ground together for 50 hours at 18°C. Twenty grams of the so-obtained powder is submitted to the treatment with TiCl₄, under the same conditions as used for the preparation of catalytic component "A2", with the only difference that the treatment is carried out once only. After filtration, washing with hexane and drying as described for the catalytic component "A2", the product obtained has the following composition by weight: Mg = 16.35%; Ti = 1.2%; Ethyl benzoate = 21.4%. Preparation of Catalytic Component "A4" By using the same equipment as described for the preparation of catalytic component "A1",72.5 g of anhy­ drous MgCl₂ (equal to 0.76 mol) and 13 g of benzonitrile (equal to 0.126 mol) are ground together for 60 hours at 20°C. Twenty grams of the so-obtained powder is submitted to two titanation treatments as described for the prepa­ ration of catalytic component "A2". The dry product obtained has the following composi­ tion by weight: Ti = 1.56%; Mg = 17.3%; benzonitrile = 10.2%. Preparation of Catalytic Component "A5" By the same procedure as used for the preparation of catalytic component "A1", 72.5 g of anhydrous MgCl₂(e­ qual to 0.76 mol) and 26.12 g of benzonitrile (equal to 0.253 mol) are ground together for 60 hours at 20°C. Twenty grams of the so-obtained powder is submitted to two titanation treatments as described for the prepa­ ration of catalytic component "A2". The dry product obtained has the following composi­ tion by weight: Ti = 0.72%; Mg = 16.7%; benzonitrile = 18.55%. Preparation of Catalytic Component "A6" Into a 250-ml glass flask provided with nitrogen­ filled plenum chamber, equipped with stirrer, reflux condenser, thermometer and temperature-controlling oil bath, 15 g of catalytic component "A1" and 150 ml of anhydrous 1,2-dichloroethane are charged. The suspension is heated under stirring for 2 hours at its reflux temperature (83.5 °C), and is then cooled to room temperature. The solid is decanted, and the liquid is separated from it by siphoning. The solid is then submitted to three washings at 50°C under stirring, each washing being carried out by 150 ml of anhydrous hexane. The product is finally dried in vacuo(residual pressure 3 mm Hg ) at 40°C for 3 hours. The composition by weight of the so-obtained product is the following: Mg = 16.95%; Ti = 1.5%; Ethyl benzoate = 19.4%. Catalytic Component "B" B1: Triisobutylaluminium in hexane solution at 20% w/v, stored under nitrogen. B2: Diethylaluminium monohydride in 15% w/v hexane solu­ tion stored under nitrogen. In the following Table the polymerization condi­ tions, together with the characteristics of the polymers obtained, the vulcanization conditions and the properties of vulcanized copolymers are reported. The vulcanization of terpolymer has been carried out (after the rubber compound having been homogenized on calender at 80°C for 10 minutes) on plate-press at 160°C for 30 minutes, with the following formulation: The determination of tension set values has been carried out on samples of polymer having useful length of 50 mm, thickness and width of 2 mm, cut along the perpen­ dicular direction relatively to the advancement direction of the compound on the roller mill. For the tension set test, the standard specimen is stretched by 200% in the metal clamp of the device and is kept resting at 23°C for 10 minutes. Subsequently, the specimen is removed from the clamp, is kept resting for 10 minutes at +23°C and the measurement is carried out soon after by using a template. Computation of Results wherein: L= length of specimen after the deformation (mm); L₀ = initial length of specimen (50 mm). The template is already calibrated to directly ex­ press the % tension set . For each test, usually two specimens are used. The two repeated tests carried out by the same operator must not give differences greater than 5%.

Claims: 1. Process for the preparation of elastomeric unsaturated polymers from ethylene with propylene and one or more diene(s) by a catalyst obtained by contacting the following components: A) a solid product containing at least on its surface compounds or mixtures of compounds comprising Mg, Ti, halogens and an electron-donor compound, the electron-donor compound / Ti molar ratio being greater than 1, the halogen atoms /Ti ratio being greater then 4; such component being furthermore chararacterized in that at least 50% by weight of the Ti compounds present in it are insoluble in Ti tetrachloride at 80°C, and that the surface area of the solid after extraction by TiCl₄ is greater than 40 m²/g. B) an organometallic compound of aluminium selected among an Al-trialkyl, an Al-dialkyl hydride and an Al-alkyl monohalide. 2. Process according to claim 1, wherein the component A) is obtained by the reaction of a liquid halogenated Ti compound with a solid composition comprising an Mg halide, selected between Mg dichloride and Mg dibro­ mide, and a complex between the Mg dihalide and the electron-donor compound preferably selected among organic esters, in particular among the esters of aromatic acids, and aromatic nitriles; said solid composition being characterized in that in its X-ray spectrum the highest-intensity line appearing in the spectrum of the halide of normal type, as defined in ASTM 3-0854 and 15-836 cards for the dichloride and the dibromide respectively, has decreased in relative intensity and has an unsymmetrically broadened shape, forming a halo showing an intensity peak shifted rela­ tively to the interplanar distance d of the highest­ intensity line, or the spectrum is characterized in that such highest-intensity line is absent, and in­ stead of it a halo with an intensity peak shifted relatively to the distance d of the highest-intensity line is present. 3. Process according to claim 1, wherein the electron­ donor compound is ethyl benzoate. 4. Process according to each of former claims for the preparation of ethylene, propylene, conjugated diene terpolymers. 5. Process according to claims 4 for the preparation of ethylene, propylene, butadiene terpolymers.

Inventors: BANZI, VIVIANO, MILANI, FEDERICO
Applicants: AUSIMONT S.P.A.
Application year: 1986
Main classification: C08F210
IPC codes: C08F210, C08F4