Manufacturing process for high cis poly(butadiene)

Abstract: Process for the manufacture of linear, substantially gel free high as 1,4 poly(butadiene), comprising the polymerisation in the presence of a catalyst, comprising at least one cobalt compound, at least one organoaluminium compound, water, and in the presence of a cycloalkane as main solvent component, containing at least one substituted benzene as polymerisation regulator, characterised in that as polymerisation regulator compounds of the general formula wherein n is an integer in the range of from 3 to 5. wherein each R represents a lower alkoxy group containing from 1 to 6 carbon atoms.

Description: The invention relates to a manufacturing process for high cis poly(butadiene). More in particular the invention relates to a process for the manufacture of cis-1,4-poly(butadiene) by polymerising 1.3 butadiene, in the presence of a catalyst comprising a mixture of a cobalt compound, at least one organoaluminium compound and water. Many commercial processes are known to produce high-cis polybutadiene in a continuous way in an aromatic solvent like toluene or benzene. However, due to environmental concerns these solvents tend to be replaced by aliphatic solvents like cyclohexane. In these solvents the polymerisation control tends to be troublesome, leading to deviations in the required polymer structure and, eventually, to increased gel content of the product. Therefore, polymerisation control agents (polymerisation regulators) have been developed as known from e.g. the British Patent Application No. 2035341. Said application discloses that, with the use of a cycloalkane having 5 to 8 carbon atoms, in particular cyclohexane, as main solvent in the polymerisation of butadiene, the polymerisation proceeded too rapidly, as a result of which it was difficult to control the polymerisation temperature, and as a consequence provided a high cis-poly(butadiene) of lower linearity which did not show the desired physical properties. In order to avoid this disadvantage, a small amount, i.e. from 0.1 to 2 wt% relative to the weight of cycloalkane, of an alkyl substituted benzene was used, which slowed down the initial polymerisation rate, so that it could be easily controlled whereas the use of significant amounts of aromatic solvents such as benzene, toluene and the like could be avoided too. The alkyl substituted benzene polymerisation regulator applied in said process had 1 to 4 alkyl substituents with each substituent having from 1 to 4 carbon atoms and preferably two or three methyl or ethyl groups. As specific examples of said alkyl substituted benzene polymerisation regulator were mentioned: toluene, 0-, m-, p-xylene or a mixture of xylene isomers, 1,3,5-trimethylbenzene (mesitylene) and other isomers of trimethylbenzene, or a mixture thereof, 1,2,4,5 tetramethylbenzene(durene) or other isomers of tetramethylbenzene (isodurene) or a mixture thereof, ethylbenzene, 1,2-, 1,3- or 1,4-diethylbenzene or a mixture of of said isomers, n-propylbenzene 1,4-3-dipropylbenzene, n-butyl-benzene or a mixture of various alkyl substituted benzenes. As cobalt catalyst component were used any organic compound such as cobalt salts of organic acids cobalt complexes and, the cobalt compound preferably being soluble in the solvent or the monomer. As an organoaluminium catalyst component preferably was used an alkyl aluminium halide, which could be used as a mono- or dialkyl aluminium halide, a mixture thereof, or a mixture of R 3 Al,R 2 AlX, RA1X 2 , or AlX 3 wherein R is alkyl of 1 to 12 carbon atoms and X is halogen and more preferably chloride. As preferred aluminium to cobalt ratios were used those in the range from 50 to 300 and more preferably from 100 to 200. Trace amounts of water were also regarded as useful components of the polymerisation catalyst system, normally added via either the solvents or the monomers. Although the alkyl-substituted benzenes may offer good polymerisation control in cyclohexane based feeds, still relatively high levels of these compounds are needed to attain the required effects. This may be a draw-back in view of environmental concerns and acceptability of the product. More effective polymerisation regulators are therefore needed,which allow sufficient kinetic control and the production of polymers within the required (existing) specification limits, at very low concentration levels. Therefore, it was an object of the present invention to provide an improved process for the manufacture of cis-1,4 poly(butadiene) providing a standardised high quality polymer, which should contain an acceptable amount of toxic chemicals. As a result of extensive research and experimentation such a process aimed at has surprisingly been found. Accordingly the present invention relates to a process of polymerising butadiene-1,3 to produce primarily linear, substantially gel free cis-1,4-poly(butadiene), comprising the polymerisation in the presence of a catalyst, comprising at least one cobalt compound, at least one organoaluminium compound, water, and in the presence of a cycloalkane as main solvent component, containing at least one substituted benzene as polymerisation regulator, characterised in that as polymerisation regulator are used compounds of the general formula wherein n is an integer in the range of from 3 to 5. wherein each R represents lower alkoxy group, containing from 1 to 6 carbon atoms and preferably 1-4. Examples of suitable modifiers may be selected from those having methoxy, ethoxy, isopropoxy, tert-butoxy, isobutoxy, n-pentoxy or isopentoxy substituents or mixtures thereof. More preferred embodiments of presently proposed polymerisation regulators are those containing 3 or 4 of the hereinbefore defined lower alkoxy groups. More preferably compounds are used wherein 3 or 4 methoxy substituents are present. The most preferred modifiers was found to be 1,3,5-trimethoxy benzene. It has been surprisingly found that the hereinbefore specified polymerisation regulators, and in particular 1,3,5-trimethoxy benzene, could be used in a significantly smaller amount to provide the same effect, in comparison with the hereinbefore discussed prior art process, i.e. less than 0.1 wt% relative to the weight of the cycloalkane solvent. Consequently the process of the present invention has been found to enable the manufacture of cis-1,4-poly(butadiene) containing significantly smaller residual amounts of said regulator. Moreover, the use of the presently proposed modifiers has enabled the manufacture of poly(butadiene) rubbers, having a well controllable linearity index. The polymerisation regulators are in general used in amounts of 100 ppm or less and in particular in amounts of from 5 to 60 ppm relative to the weight of the polymerisation feed (solvent/butadiene/butene). More preferably amounts of from 5 to 40 ppm are used. The hereinbefore specified polymerisation regulators are known per se and are manufactured and/or marketed by e.g. APIN Chemicals Ltd., Milton Park, Abingdon, United Kingdom; Indofine Chemical Comp. Inc., Somerville, NJ 8876, USA; Penta Manufacturing Company, Fairfield NJ, USA; Air Products SA, 11760, Brussels, Belgium. Examples of cycloalkanes useful in the process of the present invention are those having 5 to 8 and preferably 5 or 6 carbon atoms in the rings. They also include methyl and ethyl substituted cycloalkanes. Illustrative examples of said cycloalkanes are cyclopentane, cyclohexane, cycloheptane, cyclooctane, methylcyclopentane, methylcyclohexane, methylcycloheptane, methycyclooctane, dimethylcyclopentane, dimethylcyclohexane, dimethylcycloheptane, ethylcyclopentane, ethylcylohexane, ethylcyclooctane or mixtures thereof. Preferred are unsubstituted cycloalkanes. Most preferred solvents are cyclopentane or cyclohexane. One of the purposes of a solvent in this process is to control the polymerisation temperature by refluxing the solvent and to keep dissolved the formed polymer. Often the desired temperature control is difficult to accomplish with only one solvent. However, by selecting two or more solvents which have certain desirable boiling points, the polymerisation temperature can be relatively easily controlled. Therefore, the selection of the secondary solvent will depend primarily on its boiling point and the temperature that is to be maintained during polymerisation. Thus by "solvent" is meant either a cycloalkane solvent or a mixture of two or more solvents which is substantially free of aromatics and in particular benzene. In any event the monomer and the resulting polymer should be substantially soluble in the solvent. Useful secondary solvents are saturated aliphatic hydrocarbons for example hexane, heptane or octane; olefins having 2 to 10 carbons for example butene-1, pentene-1 or hexene-1. Various ISOPAR solvents (sold by EXXON) are also found to be useful. They are a mixture of isoparaffinic hydrocarbon fractions boiling at certain temperature ranges. For example, ISOPAR C is primarily 2,2,4-trimethylpentane and other trimethyl pentane isomers. This mixture boils at a range of approximately 206-220°F (96.7 - 104°C). The preferred secondary solvents are α-olefins, especially butene-1. The secondary solvent may be used in an amount 0 percent to 80 percent by weight of the cycloalkane solvent, and more preferably from 5 to 30 percent. If desired, a molecular weight modifier may be employed in the process of this invention in order to control the molecular weight of the product. The molecular weight may be controlled by the monomer concentration, the catalyst concentration and the ratio of the two catalyst components. However, it may be more convenient or more economical to employ a molecular weight modifier. Illustrative examples of particular useful molecular weight modifiers are non-conjugated dienes preferably those having 2 to 18 carbon atoms such as 1,2-butadiene, 1,4- and 1,5-hexadiene and the like; cyclic dienes preferably those having 6 to 12 carbon atoms such as 1,4-cyclohexadiene and 1,2 and 1,5-cyclooctadiene and the like. The molecular weight modifier is generally used in the amount of significantly less than 0.1 to 2 percent by weight of the cycloalkane, and more preferably from 200 ppm or less. The catalysts that are employed in butadiene polymerisations are well known in the art. Various cobalt and aluminium compounds which are useful as catalysts are disclosed in the patents and published patent applications mentioned above as well as U.S. patents 3,094,595 and 3,222,348, British patents 849,589; 995,957 and 1,042,172, British patent application 2035341 and German patents 1,144,922; 1,199,992 and 1,495,935. The cobalt compound can be any organic compound such as the cobalt salts of organic acids, cobalt complexes and the like, since the cobalt compound preferably should be soluble in the solvent or the monomer. Typical of such solvent or monomer soluble cobalt compounds are cobalt octoate, cobalt sorbate, cobalt adipate, cobalt 2-ethylhexanoate, cobalt stearate, cobalt acetylacetonate and the like compounds wherein the organic portion of the molecule contains about 5 to 20, preferably 8 to 18 carbon atoms and one or two carboxylic functions, as well as acetylacetonate, as are well known to those skilled in the art. The other essential catalyst component is an organoalumnium compound preferably an alkyl aluminium halide which can be used as a mono- or dialkyl aluminium halide, a mixture thereof, or a mixture of R 3 Al, R 2 AlX, RAlS 2 or AlX 3 type compounds wherein R is an alkyl and X is halogen, more preferably, the chloride. The alkyl groups normally contain 1 to 12 carbon atoms, more preferably, about 2 to 8 carbon atoms. Particularly useful are dialkyl aluminium chlorides wherein the alkyl contains 2 to 6 carbon atoms, and the so-called sesquichloride which is a mixture of aluminium trichloride and trialkyl aluminium, normally having a composition of about R 1.5-1.9 AlX 1.6-1.1 . Typical catalyst combinations are cobalt II octoate + Et 1.66 AlCl 1.33 ; cobalt II ethylhexoate + Et 1.33 AlCl + H 2 O; cobalt-acetylacetone + AlHCl 2 -ether; cobalt-3-acetylacetonate +Et 3 Al 2 Cl 3 + ethyl acetate; cobalt diacetylacetonate + Et 2 AlCl; cobalt stearate + Et 2 AlCl; cobalt acetylacetonate - Et 2 AlCl; and the like. These catalyst components are well known and clearly defined in the patent literature, including the molar ratio of cobalt to aluminium and the amounts of catalyst components used. It is normally preferred to operate in the range of aluminium to cobalt ratios between about 50:1 and 800:1. The amounts of catalyst used based on cobalt will generally be at least about 0.0005 millimol per 100 grams of butadiene up to about 5 to 10 millimols of cobalt per 100 grams. Normally, it is preferred to use from about 0.005 to about 0.5 millimols of cobalt per 100 grams of monomer. The concentration of aluminium will vary generally from as low as about 0.5 millimols to about 10 millimols or more per 100 grams of monomer, preferably about 1 to 4 millimoles. This generally means that less than about 2% by weight of total catalyst will be used. A preferred aluminium to cobalt ratio is from about 50 to about 300, and more preferably about 100 to 200. Trace amounts of water are also a useful component of the polymerisation recipe, normally added either in the solvents or monomers. The water to aluminium ratio often used is from about 0.1 to about 0.7 but ratios as low as 0.05 to as high as 0.9 are contemplated. The catalyst components may be added in any order to the polymerisation mixture or they may be premixed if desired. Solvents and/or monomer may be present during the addition of catalyst. Agitation is beneficial to obtain good heat transfer and diffusion of monomers. Batch and continuous polymerisations may be employed. It is understood, of course, that other than the catalyst water added to the polymerisation, precautions are normally taken to exclude moisture and air, particularly oxygen and oxygen-containing materials. Moisture is normally controlled to the desired amount by use of dry reactants and maintaining an inner dry atmosphere over the polymerisation materials including charging procedures. In conducting polymerisations according to the present invention, a variety of polymerisation procedures may be followed. One useful method is to charge the solvents and the monomer and then the catalyst components. The polymerisation may be conducted within a temperature range of from -35°C up to about 100°C. Normally the polymerisation is conducted at a temperature in the range of from -10°C to 50°C, and preferably between 5° and 40°C. A pressure autoclave may be employed and the pressure of the system, if any, at this temperature normally is observed. The process of this invention is particularly effective when it is employed in combination with a specific order of addition of the catalysts the solvents and the monomer. Accordingly, a preferred embodiment of the process of the present invention to produce primarily linear, gel-free cis-1,4-polybutadiene is carried out in the presence of a catalyst comprising a mixture of a cobalt compound, at least one organoaluminium compound and water, characterised in that it comprises a) adding in any order to the polymerisation vessel butadiene, water, an aluminium catalyst constituent, containing at least one chlorine containing aluminium compound, said catalyst having a chlorine to aluminium ratio of between 0.1:1 and 1.6:1; said polymerisation system containing an aluminium to cobalt ratio between 50:1 and 800:1 and a water to aluminium ratio between 0.1:1 and 0.8:1 a cycloalkane of 5 to 8 carbon atoms in the ring and b) thereafter adding a cobalt catalyst coonstituent and from 0.1 to 2 percent by weight of cycloalkane of hereinbefore specified polymerisation regulator, c) polymerising said butadiene-1,3 producing gel-free cis-1,4-polybutadiene. In the above improved process it is preferable that the molar ratio of aluminium to cobalt be in the range of 50:1 to 800:1 and more preferably 50:1 to 300:1; the molar ratio of chlorine to aluminium be in the range of 0.5:1 to 1.5:1 and the molar ratio of water to aluminium be in the range of 0.1:1 to 0.7:1 and more preferably 0.45:1 to 0.55:1. In the preferred process, the cobalt compound is pre-dissolved in an appropriate cycloalkane solvent. A convenient procedure is to first prepare a solution of a cobalt compound in a solvent such as cyclohexane the concentration of which is approximately 12 percent based on the cobalt (which solution is available commercially). Then the solution is diluted with either the same solvent or with alkylsubstituted benzene or a mixture thereof to the concentration of 0.0063 millimole/cc. of the cobalt compound. Of course, the dilution could be made to a higher or a lower concentration if desired. An appropriate amount of the dilute solution of the cobalt catalyst is then added to the main reaction vessel to which has already been added main solvent wet butadiene, and the aluminium catalyst constituent the amount of water present being such that eventually the desired water to aluminium ratio will be established. Next an appropriate amount of polymerisation regulator in predetermined amount of main solvent. The most preferred modification of the present improved process comprises mixing the starting monomer with solvent, water and the aluminium containing starting reagent and mixing this cocatalyst containing solution with the cobalt component and a polymerisation regulator, as specified hereinbefore. By "solvent" is meant a specific solvent or a mixture of two or more solvents, the mixtures being preferred. Conversion of butadiene-1,3 to cis-1,4-polybutadiene is in the range of from 30 to 90 percent, but the degree of conversion is dependent on the concentration of butadiene, total catalyst concentration, catalyst component ratios, nature of the solvent, time of reaction, temperature and possible other factors. After polymerisation has reached the desired degree of conversion, the reaction is normally stopped with an agent that reacts with the catalyst, such as water and alcohol, carboxylic acid, acetone, amine and the like, to destroy the catalyst and convert it to an oxygen insensitive material. This step is normally carried out in the absence of air. It is also often desirable to treat the reaction mixture to remove the catalyst residues. This can be effected for example by water washes, alcohol washes and the like. The polymer may be simultaneously precipitated by the addition of alcohol solvent mixtures that both destroy the catalyst and precipitate the polymer as a solid crumb which may be further washed with water or alcohol which is thereafter dried. The following examples are presented to further illustrate the process of this invention, however without restricting its scope to these embodiments. EXAMPLES Experimental Conditions The following analytical techniques for high-cis polybutadiene were employed. Microstructure determination (1,4-cis-content) was carried out with Fourier Transform InfraRed (FT-IR) spectroscopy using solutions of the polymer in CS 2 . Molecular weight determinations were carried out with Gel Permeation Chromatography using a WATERS GPC (trademark) system employing 2 "mixed bed" STYROGEL (trademark) columns in series, a differential refractive index (DRI) detector and THF as eluent. Limiting viscosity numbers (LVN) were determined of polymer solutions in toluene at 25 C using a modified SCHULKEN-SPARKS (trademark) viscometer. As a measure for the linearity of polymers prepared is used the branching index, which is the ratio of the LVN derived from the GPC (viscosity averaged) molecular weight and the real LVN: B.I. = LVN gpc (dl/g) LVN real (dl/g) All chemicals applied were handled under a dry nitrogen atmosphere. 1,3-Butadiene (Shell), 1-butene (ex-Hoek Loos) and cyclohexane (ex-Merck) were all purified prior to use by passage over alumina columns. Cobalt (II) acetylacetonate (ex-Chemische Fabriek Zaltbommel) and methoxy-substituted benzenes (ex-Aldrich Chem. Co.) were used as received. A 0.1 M solution of diethylaluminium chloride (DEAC) in cyclohexane (ex-WITCO) was used as received. Polymerisations were carried out in 0.5 L glass pressure bottles equipped with a rubber seal. After addition of ca. 150 gram of a mixture of cyclohexane, 1,-butadiene, 1-butene and water and equilibration to the desired temperature (using a thermostated water-bath tumbler) an amount of DEAC in cyclohexane is added as to adjust the water/DEAC ratio to 0.5. Typically, at a water concentration of 30 ppm, 5 ml of a 0.1 M solution of DEAC is used to give a DEAC level of ca. 400 ppm on feed. Subsequently, the required amounts of polymerisatin rate moderator and cobalt (II) acetylacetonate are added to start the polymerisation, which is allowed to proceed for 30-180 min. The polymerisation is terminated by addition of a BHT/methanol mixture and a weighed sample is taken and dried overnight in a vacuum stove at 40°C for conversion determination and polymer analysis. Comparative examples 1-6 and examples 1-6 Table 1 shows conversion data of polymerisations carried out in the presence of various concentrations of different methoxy-substituted benzenes. A feed ratio of butadiene/butene/cyclohexane of 10/55/35 is used applying a cobalt level of 1.5 ppm wt. on feed at 30°C. The conversion data demonstrate that the rate moderation efficiency of the agents tested increases strongly with the degree of methoxy-substitution. However, some of them tend to inhibit rather than moderate the polymerisation at higher concentrations (e.g. 1,2,3-TMB). The most efficient polymerisation regulator (i.e. 1,3,5-TMB) is elaborated in the next examples. Examples 7-10 and Comparative examples 7, 8 and 9 Table II shows conversion data of polymerisations carried out in the presence of various concentrations of 1,3,5-TMB and 1,2,4,5-tetramethylbenzene (durene). A feed ratio of butadiene/butene/cyclohexane of 15/55/30 is used applying a cobalt level of 1.5 ppm wt. on feed at 15°C. Again, the high efficiency of 1,3,5-TMB is demonstrated (examples 7-10)as compared to the relatively high levels of durene (comparative examples 8, 9) needed to achieve a similar rate moderation. The product data given in Table II demonstrate that 1,3,5-TMB does not affect the polymer characteristics as compared to comparative example 7. Conversion data using different methoxy-substituted benzene polymerisation regulators at 30°C. Ex Moderator Conc. (ppm) Conv. (%) (30 min) Conv. (%) (60 min.) Conv. (%) (90 min.) Comp. 1 None 0 61 71 74 Comp. 2 Anisol 200 38 48 Comp. 3 1,2-DMB 100 0 0 Comp. 4 1,3-DMB 100 43 52 Comp. 5 1,4-DMB 50 55 66 Comp. 6 1,4-DMB 100 35 44 1 1,2,3-TMB 10 56 66 70 2 1,2,3-TMB 35 30 37 3 1,2,4-TMB 10 57 68 72 4 1,2,4-TMB 35 39 46 5 1,3,5-TMB 10 55 67 72 6 1,3,5-TMB 35 37 48 Conversion data using 1,3,5-TMB and durene as polymerisation regulators at 15°C. Ex Moderator Conc. (ppm) Conv. (%) (30 min) Conv. (%) (60 min.) Conv. (%) (90 min.) Comp. 7 None 0 64 72 7 1,3,5-TMB 10 51 60 73 8 1,3,5-TMB 25 47 56 68 9 1,3,5-TMB 35 42 50 63 10 1,3,5-TMB 50 42 50 63 Comp. 8 Durene 150 55 65 78 Comp. 9 Durene 300 47 58 75 Conversion data using 1,3,5-TMB and durene as polymerisation regulators at 25°C. Ex Moderator (180 min) Conc. (ppm) Conv. (%) (60 min) Conv. (%) (90 min.) Conv. (%) (180 min.) Comp. 10 None 0 70 75 11 1,3,5-TMB 15 59 66 75 12 1,3,5-TMB 30 48 57 68 Comp. 11 Durene 100 65 71 78 Comp. 12 Durene 300 59 69 80 Polymer characterisation data using 1,3,5-TMB and durene as polymerisation regulators at 25 Ca. Ex. Moderator Conc. Mn Mw Mw/Mn Comp. 13 None 0 78000 226000 2.90 13 1,3,5-TMB 20 73300 184000 2.50 Comp. 14 1,3,5-TMB 300 75000 20500 2.70

Claims: Process for the manufacture of linear, substantially gel free high cis 1,4-poly(butadiene), comprising the polymerisation of butadiene-1,3 in the presence of a catalyst, comprising at least one cobalt compound, at least one organoaluminium compound, water, and in the presence of a cycloalkane as main solvent component, containing at least one substituted benzene as polymerisation regulator, characterised in that as polymerisation regulator compounds of the general formula wherein n is an integer in the range of from 3 to 5. wherein each R represents a lower alkoxy group containing from 1 to 6 carbon atoms are used. Process according to claim 1, characterised in that each R represents a lower alkoxy group containing from 1 to 4 carbon atoms. Process according to claim 1, characterised in that the polymerisation regulator contain 3 or 4 lower alkxoy groups. Process according to claim 3, characterised in that 3 or 4 methoxy groups are present. Process according to claim 4, characterised in that 1,3,5-trimethoxy benzene is used as polymerisation regulator. Process according to claims 1-5, characterised in that the polymerisation regulator is used in amounts of from 5 to 60 ppm. Process according to claim 7, characterised in that the polymerisation regulator is used in amounts of from 5 to 40 ppm. Process according to any of the claims 1-7, characterised in that as main solvent a cycloalkane, having 5 or 6 carbon atoms is used.

Inventors: DE BOER-WILDSCHUT MARIJKE, KERSTEN MARIA JOHANNA ELISABET, VAN DER AREND JOHANNES C M, VAN DER HUIZEN ADRIAAN ALBERT, DE BOER-WILDSCHUT, MARIJKE, KERSTEN, MARIA JOHANNA ELISABETH, VAN DER AREND, JOHANNES C. M., VAN DER HUIZEN, ADRIAAN ALBERT
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1996
Main classification: C08F136
IPC codes: C08F136, C08F4