Copolymers of ethylene and an alpha-olefin and catalytic production thereof

Abstract: Ethylene (35-60 mols) and a C₃₋₁₀ α-olefin (65-­ 40 mols) are copolymerized at a temperature of 40 to 80 o C with a catalyst of (a) an oxyvanadium compound, (b) an organoaluminium compound and (c) a halogenated hydrocarbon ester, e.g. a perchlorocrotonic acid ester, in a mol ratio of (b) to (a) of ≧ 2.5 and of (c) to (a) of ≧ 1.5, in a hydrocarbon solvent. The polymer has a molar ratio of ethylene: α-olefin of 88:12 - 98:2, a number average mol. wt. of 35,000 - 80,000 and a ratio of wt. number average mol wt. of 1.8:1 - 3.0:1 determined by GPC. It has good trans­ parency and is moldable to a film which is heat-sealable at low temperature.

Description: This invention relates to a copolymer of ethylene and an α-olefin and a process for producing the same. More particularly, it relates to an ethylene-α-olefin copolymer excellent in transparency and low-temperature heat-sealing properties and to a process for producing such an ethylene-α-olefin copolymer. Ethylene-α-olefin copolymers exhibit excellent characteristics such as heat resistance, weather resistance and ozone resistance and have therefore found many uses as automobile materials, constructional materials, industrial materials and resin modifiers. In particular, ethylene-α-olefin copolymers having a high ethylene content are soft resins having properties midway between rubbers and crystalline plastics and are now in growing demand as packaging film, etc. Inter alia , copolymers obtained by copolymerizing ethylene and an α-olefin in the presence of a titanium-based polymerization catalyst are known as linear low-density polyethylene (hereinafter abbreviated as LLDPE) and are widely employed. However, films produced from LLDPE do not always satisfy requirements of low temperature heat-sealing properties and transparency. The insufficient transparency or heat-sealing properties of the LLDPE are considered attributed to non-uniform composition of ethylene and α-olefin in the copolymer and broad molecular weight distribution. JP-A-63020309 discloses random copolymers of ethylene and butene containing 85 to 95 mol% ethylene with a ratio of weight average to number average molecular weight of 2 to 5 and molecular weight of 30,000 to 200,000 which is said to have good mechanical strength and flexibility; it has two melting points as determined with a differential scanning calorimeter. GB-A-2093047 describes copolymers of ethylene with 0.5 to 8 mol% of an alpha-olefin having a ratio of weight average molecular weight to number average molecular weight of from 2.0 to 5.0, a number molecular weight of 8600 to 54000 and exhibiting a single melting point as determined by differential thermal analysis which is slightly above 105°C, as shown in the examples; they can be formed into transparent films. GB-A-1403372 discloses the polymerisation of ethylene with to 20 mol% of alpha-olefins in the presence of a catalyst which can comprise a vanadium compound, an organoaluminium compound and a halogenated organic ester, in a solvent. On the other hand, several other processes for producing ethylene-α-olefin copolymers using a vanadium-based catalyst have been proposed. For example, JP-B-46-21212 (the term "JP-B" as used herein means an "examined published Japanese patent application") discloses a process of solution polymerization of ethylene and an α-olefin using a catalyst system comprised of a vanadium compound and an organoaluminum compound. According to this process, a copolymer is obtained in the form of a uniform solution, i.e., as dissolved in a polymerization solvent. However, the vanadium compound used greatly reduces in catalytic activity as the polymerization temperature increases. For example, as shown in the working examples of this patent publication, the polymerization activity becomes too low to be suited for practical use in a high temperature range, e.g., at 100°C, only to produce a copolymer having broad molecular weight distribution and having a solvent extractable content. JP-B-47-26185 discloses a process for producing an ethylene-α-olefin copolymer by using a halogenated lower aliphatic hydrocarbon or a hydrocarbon having from 3 to 5 carbon atoms as a polymerization solvent and a combination of a VOX₃ compound and an organoaluminum compound as a catalyst system. Polymerization in a halogenated hydrocarbon produces a polymer as a precipitate insoluble in the polymerization solvent, forming a slurry having a low viscosity as a whole. This is economically advantageous in stirring or transporting the system but, in turn, there are problems arising from decomposition of the halogenated hydrocarbon, such as corrosion of apparatus and storage stability of the polymer. In the case of slurry polymerization in a hydrocarbon solvent having 3 to 5 carbon atoms, the closeness of the boiling point of this solvent to that of the ethylene-copolymerizable α-olefin, particularly propylene or 1-butene, gives rise to a great problem in separating the unreacted monomer and the polymerization solvent in the purification step. Further, from an economical viewpoint, this process is not always recognized as advantageous since hydrocarbons having 3 to 5 carbon atoms have low boiling points and therefore require a freezing apparatus for liquefication and a pressure-resistant apparatus as well as a cooling medium. Furthermore, the process requires large-sized equipment for an ashing step for removing the catalyst components incorporated into the produced polymer particles. JP-B-55-24447 discloses a process for producing an ethylene-1-butene copolymer having an ethylene content of from 85 to 95 mol%, in which copolymerization is effected at a temperature of from -20° to 30°C in an aliphatic hydrocarbon having from 6 to 15 carbon atoms as a polymerization solvent in the presence of a catalyst system composed of a soluble vanadium compound and an organoaluminum halide. Similarly, JP-A-63-17912 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describes a process for copolymerizing ethylene and an α-olefin at from -20° to 30°C using a catalyst system composed of a soluble vanadium compound and a chlorinated organoaluminum compound. Both of these processes relate to slurry polymerization with the difference being that the Al/V atomic molar ratio is from 2/1 to 50/1 in the former process and from 55/1 to 170/1 in the latter process. According to either process, since polymerization is carried out at a relatively low temperature (from -20° to 30°C), a large quantity of a cooling medium and energy for driving a freezing device are necessary. In addition, the reaction rate attained is so low that the retention time in the reaction vessel becomes long, increasing the overall volume of the reaction vessel, which results in large consumption of stirring power in the reaction vessel. In short, when ethylene-α-olefin copolymers having a high ethylene content are produced by slurry polymerization, that is, in a system in which a part of the copolymer produced is insoluble in a polymerization solvent so that the reaction proceeds while the insoluble copolymer is in a precipitated state, by the conventional processes, it is necessary to make a proper choice of a solvent, and the reaction should be conducted at low temperatures, which is disadvantageous from the standpoint of equipment and energy. On the other hand, in the case of solution polymerization in a system in which copolymerization proceeds while the whole copolymer is dissolved in the solvent, the conventional processes require relatively high temperatures and suffer from reduction of catalyst efficiency, resulting in economic disadvantage. From all these considerations, it has been much desired to develop a slurry polymerization technique which can be effected at a midway temperature, more specifically at around 40 to 65°C at which a vanadium-based catalyst exerts the possible highest activity, which would be of advantage from the standpoint of equipment, energy and cost. The most relevant process so far proposed in this connection is found, e.g., in JP-B-46-11028. According to the disclosed technique, however, the resulting copolymer has a very non-uniform composition and a broad molecular weight distribution, thereby possessing poor strength and poor transparency. One object of this invention is to eliminate the disadvantages associated with the conventional processes and to provide a process for producing an ethylene-α-olefin copolymer having a narrow molecular weight distribution and a uniform composition by slurry polymerization, with industrial advantages from the standpoint of equipment, energy and cost. Another object of this invention is to provide an ethylene-α-olefin copolymer having a narrow molecular weight distribution, a uniform composition, and a low solvent extractable content, thereby exhibiting satisfactory transparency and excellent low-temperature heat-sealing properties. The inventors have conducted extensive investigations on a process for producing an ethylene-α-olefin copolymer having a narrow molecular weight distribution and a uniform composition. As a result, it has now been found that slurry polymerization can be carried out at a low viscosity by using a three-component catalyst system comprising a specific vanadium compound, a specific organoaluminum compound and a specific halogenated ester compound at a specific mixing ratio and by properly selecting a copolymerization temperature, a molar ratio of ethylene and an α-olefin, and a copolymerization solvent to be used. It has also been found that an ethylene-α-olefin copolymer having the above-described properties can be obtained by slightly elevating the temperature of the system after completion of the copolymerization thereby making it possible to handle the reaction system as a uniform solution and facilitating ashing of the copolymer. The present invention has been completed based on these findings. That is, in one embodiment the present invention provides an ethylene-α-olefin copolymer which comprises ethylene and an α-olefin having from 3 to 10 carbon atoms, has an ethylene/α-olefin molar ratio of from 88/12 to 98/2, and which has a number average molecular weight of from 35,000 to 80,000 and a weight average molecular weight/number average molecular weight ratio of from 1.8/1 to 3.0/1 as determined by gas permeation chromatography (GPC) and which shows a single endothermic peak of up to 105°C as determined by means of a differential scanning calorimeter and which is obtained by use of a polymerization catalyst containing vanadium. Further, in another embodiment the present invention provides a process for producing said ethylene-α-olefin copolymer, which comprises copolymerizing ethylene and an α-olefin having from 3 to 10 carbon atoms at an ethylene/α-olefin molar ratio of from 35/65 to 60/40 and at a temperature of from 40 to 80°C using a catalyst system composed of (a) a vanadium compound represented by formula: VO(OR) n X 3-n wherein R represents a hydrocarbon group; X represents a halogen atom; and n is a number of from 0 to 3, (b) an organoaluminium compound represented by formula: R' m AℓX 3-m wherein R' represents a hydrocarbon group; X represents a halogen atom; and m represents a number of from 1 to 3, and (c) a halogenated ester compound represented by formula: wherein R'' represents an organic group derived from a hydrocarbon group having from 1 to 20 carbon atoms by substituting a part or all of the hydrogen atoms thereof with a halogen atom; and R''' represents a hydrocarbon group having from 1 to 20 carbon atoms, at an organoaluminum compound/vanadium compound molar ratio of 2.5/1 or more and at a halogenated ester compound/vanadium compound molar ratio of 1.5/1 or more, in a hydrocarbon solvent in which the resultant polymer can be present in both dissolved and insoluble form at a temperature below 70°C. The process of the present invention is characterized in that the copolymerization is carried out in a system where a hydrocarbon solvent-soluble polymer and a hydrocarbon solvent-insoluble polymer coexist, more specifically, in a mixed system comprising a dissolved polymer and insoluble fine polymer particles having a particle size of not more than 0.5 mm. Such a mixed polymerization system, when held at 40°C, contains 95% by weight or more of the hydrocarbon solvent-insoluble polymer based on the total polymer. In this case, the system has a low viscosity characteristic of a slurry polymerization system. When the system is held at 70°C or higher, the system becomes a uniform solution. Important in the present invention are choices of a combination of catalyst components, a copolymerization solvent, and a copolymerization temperature. Specific examples of the vanadium compound represented by formula VO(OR) n X 3-n , wherein R, X, and n are as defined above, include VOCl₃, VO(OCH₃)Cl₂, VO(OCH₃)₂Cl, VO(OCH₃)₃, VO(OC₂H₅)Cl₂, VO(OC₂H₅)₂Cl, VO(OC₂H₅)₃, VO(OC₃H₇)Cl₂, VO(OC₃H₇)₂Cl, VO(OC₃H₇)₃, VO(O-iso-C₃H₇)Cl₂, VO(O-iso-C₃H₇)₂Cl, VO(O-iso-C₃H₇)₃ and mixtures thereof. These vanadium compounds except for VOCl₃ can easily be prepared by reacting VOCl₃ with an alcohol or by reacting VOCl₃ with VO(OR)₃. Preferred of them are those wherein 0≦n≦1, i.e., VOCl₃, VO(OCH₃)Cl₂, VO(OC₂H₅)Cl₂, VO(OC₃H₇)Cl₂, and VO(O-iso-C₃H₇)Cl₂, from the viewpoint of obtaining copolymers having a narrow molecular weight distribution and a uniform composition. In particular, VOCl₃ (n=0) is the most preferred. The copolymerization system in the co-presence of a hydrocarbon solvent-insoluble polymer and a hydrocarbon solvent-soluble polymer may also be achieved by the use of the vanadium compounds wherein 1<n≦3, e.g., VO(OCH₃)₂Cl, VO(OCH₃)₃, VO(OC₂H₅)₂Cl, VO(OC₂H₅)₃, VO(OC₃H₇)₂Cl, VO(OC₃H₇)₃, VO(O-iso-C₃H₇)₂Cl and VO(O-iso-C₃H₇)₃. However, the ethylene-α-olefin copolymers obtained from such a system have two endothermic peaks in differential thermal analysis (DTA) by means of a differential scanning calorimeter (DSC), one in the region between 80°C and 105°C and the other in the region exceeding 105°C. Some of such copolymers may suffer from reduction of heat-sealing properties or transparency. The organoaluminum compound represented by formula R' m AlX 3-m , wherein R', X and m are as defined above, which can be used in the catalyst system includes (C₂H₅)₂AlCl, (C₄H₉)₂AlCl, (C₆H₁₃)₂AlCl, (C₂H₅) 1.5 AlCl 1.5 , (C₄H₉) 1.5 AlCl 1.5 , (C₆H₁₃) 1.5 AlCl 1.5 , C₂H₅AlCl₂, C₄H₉AlCl₂ and C₆H₁₃AlCl₂. From the standpoint of reaction rate and yield, preferred of them are those wherein 1≦m≦2, with (C₂H₅) 1.5 AlCl 1.5 being more preferred. The halogenated ester compound represented by formula wherein R'' and R''' are as defined above, which can be used as a catalyst component preferably includes those wherein R'' is a group in which all the hydrogen atoms thereof are substituted with a halogen atom, more preferably perchlorocrotonic acid esters. Specific examples of the halogenated ester compound are ethyl dichloroacetate, methyl trichloroacetate, ethyl trichloroacetate, methyl dichlorophenylacetate, ethyl dichlorophenylacetate, methyl perchlorocrotonate, ethyl perchlorocrotonate, propyl perchlorocrotonate, isopropyl perchlorocrotonate, butyl perchlorocrotonate, cyclopropyl perchlorocrotonate and phenyl perchlorocrotonate. In the copolymerization system, the vanadium compound concentration ranges from 0.00005 mmol/ℓ to 5 mmols/ℓ, preferably from 0.0001 mmol/ℓ to 1 mmol/ℓ. The molar ratio of the organoaluminum compound to the vanadium compound should be 2.5/1 or more, preferably from 2.5/1 to 30/1, and the molar ratio of the halogenated ester compound to the vanadium compound should be 1.5/1 or more. If the organoaluminum compound/vanadium compound molar ratio is less than 2.5/1, the copolymerization reaction becomes extremely unstable, resulting in stopping or failing to obtain a desired copolymer having a narrow molecular weight distribution. If the halogenated ester compound/ vanadium compound molar ratio is less than 1.5/1, the resulting copolymer has a broad molecular weight distribution. The copolymerization according to the present invention is carried out in a hydrocarbon solvent. The hydrocarbon solvent to be used includes aliphatic hydrocarbons, e.g., hexane, heptane, octane, decane, dodecane and kerosine; alicyclic hydrocarbons, e.g., cyclohexane, methylcyclopentane and methylcyclohexane; and aromatic hydrocarbons, e.g., benzene, toluene and xylene. Preferred of them are hexane, heptane, octane and cyclohexane. The solvent may be partly or wholly replaced with an α-olefin, e.g., propylene, 1-butene, 1-pentene and 1-hexene. The copolymerization temperature can be from 40 to 80°C, preferably from 40 to 65°C. If it is lower than 40°C, the reaction rate is seriously reduced and, in addition, a specific equipment for cooling or freezing would be necessary to remove the reaction heat. On the other hand, at temperatures higher than 80°C, the whole copolymer produced becomes soluble in the solvent throughout the copolymerization system to increase the viscosity of the system, thus so much increasing the power required for stirring and mixing. At even higher temperatures, the polymerization activity of the catalyst is lost, failing to produce a copolymer. The copolymerization is carried out under atmospheric pressure or under an elevated pressure, preferably at a pressure of from 1 to 29 Pa x 10⁵ (1 to 30 kg/cm²), more preferably from 1 to 19,5 Pa x 10⁵ (1 to 20 kg/cm²). The retention time of the copolymerization reaction mixture in the copolymerization vessel ranges from 10 to 180 minutes, preferably from 20 to 120 minutes, in average. In order to assure good reproducibility in obtaining an ethylene-α-olefin copolymer with satisfactory physical properties, the total polymer concentration in the copolymerization system is adjusted not to exceed 15% by weight, preferably not to exceed 12% by weight. The copolymerization is effected in a system where a hydrocarbon solvent-insoluble polymer and a hydrocarbon solvent-soluble polymer coexist during stirring. It is preferable to control the molar ratio of ethylene and α-olefin to be charged in such a manner that the hydrocarbon solvent-insoluble polymer content may amount to 95% by weight or more at 40°C or the total polymer may solely comprise the hydrocarbon solvent-soluble polymer at 70°C. In such a copolymerization system, the copolymerization temperature is preferably set at from 40 to 65°C, more preferably at from 40 to 55°C. In this particular system, since the reaction proceeds with the hydrocarbon solvent-insoluble polymer being suspended in the form of fine particles of 0.5 mm or smaller in diameter, the viscosity of the system can be kept low, the stirring power energy can be minimized, and the reaction heat can easily be removed. Moreover, a satisfactory mixing state of the catalyst and the monomers can be obtained, as is advantageous for obtaining a polymer having a narrow molecular weight distribution and a uniform composition. The temperature in the downstream side of the reaction vessel, on the other hand, is controlled at 70°C or higher, whereby all the polymer present there becomes soluble in the solvent. Such temperature control can thus eliminate the problem due to precipitated polymer particles generally encountered in slurry polymerization systems effected on an industrial scale, i.e., sedimentation and deposition of the polymer particles in regions of insufficient flow in the plant or obstruction of piping. The weight ratio of the hydrocarbon solvent-insoluble polymer and the hydrocarbon solvent-soluble polymer can be determined by filtering the reaction mixture sampled from the copolymerization system through a metallic net of 300 mesh to separate into hydrocarbon solvent-soluble matter and hydrocarbon solvent-insoluble matter, removing the hydrocarbon solvent from each matter by drying, and weighing each of the resulting solids. The 300 mesh sieve has an opening size of 0.048 mm. The ethylene-α-olefin copolymer according to the present invention has an ethylene/α-olefin molar ratio of from 88/12 to 98/2 and a ratio of weight average molecular weight ( M w) to number average molecular weight ( M n), M w/ M n (hereinafter referred to as a Q value), of from 1.8/1 to 3.0/1 as determined by GPC. The ethylene-α-olefin copolymer satisfying these conditions exhibits excellent performance properties in terms of strength at break, elongation, and surface hardness as measured according to JIS K-6301. Preferred ethylene-α-olefin copolymers which are particularly excellent in heat-sealing properties and transparency have an ethylene/α-olefin molar ratio of from 92/8 to 96/4 and a Q value of from 1.8/1 to 2.6/1, and shows said endothermic peak being between 80°C and 105°C. The ethylene-α-olefin copolymer according to the present invention has a number average molecular weight of from 35,000 to 80,000 as determined by GPC and shows a single endothermic peak as determined by a DSC. If it is less than 35,000, the copolymer produced has an insufficient strength. On the other hand, if it exceeds 80,000, the molding processability is poor. GPC as used herein was conducted under the following measurement conditions: GP Chromatograph: 150 C Model, manufactured by Waters Corp. Column: Shodex® AC-80M, manufactured by Shoda Denko K.K. Sample Volume: 300 µℓ (polymer conc.: 0.2% by weight) Flow Rate: 1 ml/min Temp.: 135°C Solvent: 1,2,4-trichlorobenzene A calibration curve was prepared in a usual manner by using a standard polystyrene produced by Tosoh Corporation. Data were processed by the use of Data Processor CP-8 Model III, manufactured by Tosoh Corporation. Molecular weight control of the ethylene/α-olefin copolymer can be done by addition of hydrogen, diethylamine, ally] chloride, pyridine-N-oxide, etc., with H₂ being particularly preferred. The present invention is now illustrated in greater detail by way of the following Examples, Comparative Examples, Reference Examples illustrating films of the copolymer and Comparative Reference Examples. EXAMPLE 1 Ethylene and 1-butene were continuously copolymerized by using a 5 ℓ-volume stainless steel polymerization vessel equipped with a stirring blade. Hexane as a polymerization solvent was continuously fed into the lower part of the vessel at a rate of 5 ℓ/hr, while a polymerization mixture was continuously withdrawn from the upper part of the vessel so as to maintain the volume of the polymerization mixture in the vessel at 5 ℓ. As a catalyst system, vanadium oxytrichloride, ethylaluminum sesquichloride and n-butyl perchlorocrotonate were continuously fed to the upper part of the vessel at a rate of 0.050 mmol/hr, 1.2 mmols/hr and 0.12 mmol/hr, respectively. Ethylene and 1-butene as monomers were continuously fed to the lower part of the vessel at a feed rate of 230 g/hr and 360 g/hr, respectively. Molecular weight control was effected with hydrogen. The copolymerization temperature was controlled at 55°C by circulating cooling water through a jacket provided around the vessel. The copolymerization reaction was carried out under the above-recited conditions to thereby produce an ethylene-1-butene copolymer in the form of a mixture of polymerization solvent-insoluble matter and polymerization solvent-soluble matter. A small amount of methanol was added to the polymerization mixture withdrawn from the reaction vessel to stop the reaction. Any unreacted monomers were removed from the mixture, the mixture was washed with water, and the solvent was removed by stripping with steam in a large quantity of water. The collected copolymer was dried at 80°C under reduced-pressure for one day. There was thus obtained an ethylene-1-butene copolymer at an output rate of 170 g/hr. The ethylene content of the resulting copolymer was found to be 96.1 mol% by infrared absorption analysis. GPS analysis revealed that the copolymer had an M w of 112,000 and an M n of 55,000, giving a Q value of 2.2/1. The DTA curve of the copolymer obtained by the use of DSC had a single fusion peak, showing a melting point (Tm) at 99°C and a heat of fusion (ΔHm) of 19 cal/g. The polymerization mixture withdrawn from the reaction vessel was filtered through a metallic net of 300 mesh to separate into a solvent-insoluble matter and a solvent-soluble matter, and each of them was weighed to give an insoluble matter/soluble matter weight ratio of 61/39. When the copolymer was press molded, the resulting molded article exhibited highly satisfactory transparency and had a strength at break of 330 kgf/cm², an elongation at break of 710%, and a surface hardness of 93, each measured in accordance with JIS K-6301 the strength at break here and in tables 2 and 4 are converted to Pa by multiplying by 0.9806 x 10⁵. EXAMPLES 2 TO 5 Ethylene and 1-butene were copolymerized in the same manner as in Example 1, except for altering the conditions as shown in Table 1. Each of the resulting copolymers was analyzed and evaluated in the same manner as in Example 1, and the results obtained are shown in Table 2. EXAMPLES 6 AND 7 Copolymerization was carried out in the same manner as in Example 1, except for replacing 1-butene with propylene and altering the polymerization conditions as shown in Table 1. Each of the resulting ethylene-α-olefin copolymers was analyzed and evaluated in the same manner as in Example 1, and the results obtained are shown in Table 2. COMPARATIVE EXAMPLES 1 AND 2 Copolymerization was carried out in the same manner as in Example 1, except for using, as catalyst components, vanadium oxytrichloride and ethylaluminum sesquichloride only but using no n-butyl perchlorocrotonate and altering the reaction conditions as shown in Table 1. Each of the resulting copolymers was analyzed and evaluated in the same manner as in Example 1, and the results obtained are shown in Table 2. COMPARATIVE EXAMPLE 3 Copolymerization was carried out in the same manner as in Example 1, except for changing the ethylene feed rate to 100 g/hr and the 1-butene feed rate to 500 g/hr. The copolymer produced was totally soluble in the hexane solvent, and the system became a viscous solution. The copolymer recovered was rubber-like and had a low strength at break of 140 kgf/cm². COMPARATIVE EXAMPLE 4 Copolymerization was carried out in the same manner as in Example 1, except for changing the ethylene feed rate to 300 g/hr, the 1-butene feed rate to 300 g/hr, and the polymerization temperature to 25°C. As a result, the copolymerization system became a slurry in which most of the copolymer produced was suspended in the hexane solvent as insoluble fine particles, a part of the copolymer particles being found deposited onto the inner wall of the piping in the downstream side of the outlet of the vessel. The recovered copolymer had a low elongation at break of 420%. EXAMPLE 8 Ethylene and 1-butene were continuously copolymerized by using the same polymerization vessel as used in Example 1 to which was connected a 10 ℓ-volume SUS-made pressure-resistant stirring tank equipped with a stirring blade, a jacket, and an outlet for withdrawing gasified components at the top thereof (hereinafter referred to as degassing apparatus). Hexane as a polymerization solvent was continuously fed to the lower part of the vessel at a feed rate of 5 ℓ/hr, while the polymerization mixture was continuously withdrawn from the upper part of the vessel so as to maintain the volume of the polymerization mixture in the vessel at 5 ℓ and introduced into the degassing apparatus. The polymerization mixture was further continuously withdrawn from the side of the degassing apparatus so as to control the volume of the polymerization mixture in the apparatus at 5 ℓ. As a catalyst system, vanadium oxytrichloride, ethylaluminum sesquichloride and ethyl dichlorophenylacetate were continuously fed to the lower part of the vessel at a rate of 0.020 mmol/hr, 0.55 mmol/hr, and 0.060 mmol/hr, respectively. Ethylene and 1-butene were continuously fed to the lower part of the vessel at a rate of 155 g/hr and 175 g/hr, respectively. Molecular weight control was effected with hydrogen. The copolymerization temperature was controlled at 55°C by circulating cooling water through a jacket provided around the vessel. The copolymerization reaction was carried out under the above-recited conditions to thereby produce an ethylene-1-butene copolymer in the form of a mixture of polymerization solvent-insoluble matter and polymerization solvent-soluble matter. The polymerization mixture was continuously withdrawn from the vessel and introduced into the degassing apparatus. A small amount of methanol was added to the polymerization mixture in the degassing apparatus to stop the reaction. The inner temperature of the apparatus was controlled at 40°C while removing the unreacted monomers. The mixture withdrawn from the degassing apparatus assumed a slurry condition in which copolymer particles having a particle size of from about 0.01 to 0.1 mm were suspended in the hexane solvent. The polymerization mixture sampled from the degassing apparatus was filtered through a metallic net of 300 mesh to separate it into polymerization solvent-insoluble matter and polymerization solvent-soluble matter, and each of them was weighed to give an insoluble matter/soluble matter weight ratio of 98/2. On the other hand, the polymerization mixture sampled from the polymerization vessel was found to have an insoluble matter/soluble matter weight ratio of 44/56. While continuing the polymerization, warm water was then circulated through the jacket of the degassing apparatus to control the inner temperature at 70°C. The polymerization mixture withdrawn from the apparatus contained no solid particles and, instead, the copolymer produced was found to be in a dissolved state in the hexane solvent. Polymerization was further continued, and the inner temperature of the degassing apparatus was cooled to 40°C. Then, the polymerization mixture returned to the slurry state comprising suspended copolymer particles. The structural values of the copolymer sampled from the polymerization mixture kept at 70°C were consistent with those of the copolymer sampled from the mixture cooled to 40°C within measurement errors. The resulting copolymer was found to have an ethylene content of 94 mol% by infrared absorption analysis; an M w of 98,000, an M n of 49,000 by GPC analysis, giving a Q value of 2.0/1; a single fusion peak showing a Tm of 95°C and a ΔHm of 23 cal/g by DSC. Transparency and mechanical properties of the copolymer were evaluated in the same manner as in Example 1. The polymerization conditions used are shown in Table 3, and the results of analyses and evaluations are shown in Table 4. EXAMPLES 9 AND 10 AND COMPARATIVE EXAMPLES 5 AND 6 Copolymerization was carried out in the same manner as in Example 8, except for changing the feed rates of the polymerization solvent, organoaluminum compound, halogenated ester compound, ethylene and 1-butene or changing the kind or amount of the vanadium compound as shown in Table 3. Each of the resulting copolymers was analyzed and evaluated in the same manner as in Example 1, and the results obtained are shown in Table 4. REFERENCE EXAMPLES 1 TO 3 Each of the copolymers obtained in Examples 8, 9 and 10 was mixed with 0.1% by weight of calcium stearate, 0.2% by weight of octadecyl-3-(3',5'-di-t-butyl-4-hydroxyphenyl)propionate ("IRGANOX® 1076" produced by Chiba-Geigy AG), and 0.05% by weight of tris-nonylphenyl phosphite ("ANTIGENE® TNP" produced by Sumitomo Chemical Co., Ltd.). The resulting compound was pelletized and molded into a film having a thickness of 30 µm. Physical properties of the film are shown in Table 5. COMPARATIVE REFERENCE EXAMPLES 1 TO 3 Each of the copolymers obtained in Comparative Examples 5 and 6 and an LLDPE was compounded with additives and molded into a film in the same manner as in Reference Examples 1 to 3. Physical properties of each of the resulting films are shown in Table 5. As described above, the present invention provides an ethylene-α-olefin copolymer having a narrow molecular weight, a uniform composition, and a small solvent extractable content and thereby exhibiting excellent transparency and low-temperature heat-sealing properties. The process according to the present invention for producing such an ethylene-α-olefin copolymer, in which copolymerization is carried out in such a system that a hydrocarbon solvent-insoluble polymer and a hydrocarbon solvent-soluble polymer coexist, is advantageous from the standpoint of equipment, energy and cost.

Claims: A copolymer of ethylene and an α-olefin having from 3 to 10 carbon atoms, characterised by an ethylene/α-olefin molar ratio of from 88/12 to 98/2 and a number average molecular weight of from 35,000 to 80,000 and a ratio of its weight average molecular weight to its number average molecular weight of from 1.8/1 to 3.0/1 as determined by gas permeation chromatography and which shows a single endothermic peak of up to 105°C as determined by means of a differential scanning calorimeter, and which is obtained by use of a polymerization catalyst containing vanadium. A copolymer as claimed in Claim 1, wherein the ethylene/α-olefin molar ratio is from 92/8 to 96/4, the weight average molecular weight/number average molecular weight ratio is of from 1.8/1 to 2.6/1, said endothermic peak being in the range of from 80°C to 105°C. A process for producing a copolymer of ethylene and an α-olefin copolymer as claimed in claim 1 or 2, which comprises copolymerizing ethylene and an α-olefin having from 3 to 10 carbon atoms in solution in the presence of a catalyst system comprising a vanadium compound and an organoaluminium compound, characterised by an ethylene/α-olefin molar ratio of from 35/65 to 60/40, a temperature of from 40 to 80°C, a catalyst system composed of (a) a vanadium compound represented by the formula: VO(OR) n X 3-n wherein R represents a hydrocarbon group, X represents a halogen atom and n is a number of from 0 to 3, (b) an organoaluminium compound represented by the formula: R' m AℓX 3-m wherein R' represents a hydrocarbon group, X represents a halogen atom and m represents a number of from 1 to 3, and (c) a halogenated ester compound represented by the formula: wherein R'' represents an organic group derived from a hydrocarbon group having from 1 to 20 carbon atoms by substituting a part or all of the hydrogen atoms thereof with a halogen atom and R''' represents a hydrocarbon group having from 1 to 20 carbon atoms, at a molar ratio of organoaluminium compound to vanadium compound of 2.5/1 or more and at a molar ratio of halogenated ester compound to vanadium compound of 1.5/1 or more, in a hydrocarbon solvent in which the resultant polymer can be present in both dissolved and insoluble form at a temperature below 70°C, so as to produce a copolymer as claimed in Claim 1. A process as claimed in Claim 3 wherein the initial α-olefin has from 4 to 8 carbon atoms, the ethylene/α-olefin molar ratio is from 40/60 to 58/42, in the catalyst system n is a number of from 0 to 1, and m represents a number of from 1 to 2; and the organoaluminium compound/vanadium compound molar ratio is from 2.5/1 to 30/1. A process as claimed in Claim 3 or 4, which is carried out at a temperature of 40 to 65°C. A process as claimed in Claim 3, 4 or 5, wherein said hydrocarbon solvent-insoluble polymer in said system is 95% by weight or more based on the total amount of polymer at 40°C and is 100% by weight based on the total polymer at 70°C. A process as claimed in any of Claims 3 to 6, wherein n in the formula representing the vanadium compound is 0. A process as claimed in any of Claims 3 to 7, wherein m in the formula representing the organoaluminium compound is 1.5. A process as claimed in any of Claims 3 to 8, wherein said halogenated ester compound is a perchlorocrotonic acid ester. A process as claimed in any of Claims 3 to 9, wherein said α-olefin is 1-butene.

Inventors: IMAI AKIO, SUGIMORI KIYOYUKI, TAKANE MINORU, YAMAMOTO KEISAKU, IMAI, AKIO, SUGIMORI, KIYOYUKI, TAKANE, MINORU, YAMAMOTO, KEISAKU
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1989
Main classification: C08F210
IPC codes: C08F210, C08F4