Polymer preparation

Abstract: Process for the preparation of polymers, wherein polymers of carbon monoxide with ethene and/or propene and optionally in addition with one or more other α-olefins are prepared by contacting the monomers in the presence of hydrogen with a catalyst containing a Group VIII metal and a phosphorus bidentate ligand in which two dialkylphosphino groups occur, between which a divalent organic bridging group is present and in which the bridge connecting the two phosphorus atoms to each other contains at least two carbon atoms.

Description: The invention relates to a process for the preparation of polymers of carbon monoxide with one or more α-olefins. It is known, e.g. from EP-A-121965, that linear polymers of carbon monoxide with ethene and/or propene and optionally in addition with one or more other α-olefins in which polymers the units from carbon monoxide on the one hand and the units from the olefins on the other hand are present in a substantially alternating arrangement can be prepared by contacting the monomers with a catalyst composition containing a Group VIII metal and a phosphorus bidentate ligand of the general formula R₁R₂P-R-PR₃R₄ in which R₁ to R₄ represent identical or different monovalent aromatic or aliphatic hydrocarbon groups and R is a divalent organic bridging group containing at least two carbon atoms in the bridge connecting the two phosphorus atoms to each other. Using these catalyst compositions, linear alternating polymers are obtained with an average molecular weight, calculated as number average ( M n ), of more than 10,000. For some applications there is a need for such polymers with a considerably lower average molecular weight. These polymers can be used as such or can serve as starting material for the preparation of other valuable polymers by chemical modification. The carbonyl groups present in the polymers as functional groups can be converted by chemical reaction at least partly into a variety of other functional groups. This chemical modification changes the properties of the polymers and they become eligible for applications for which the original polymers were unsuitable or less suitable. Examples that can be mentioned of chemical reactions which can be applied to the low molecular weight polymers are the conversion to polyalcohols by catalytic hydrogenation, the conversion to polypyrroles by reaction with primary amines or ammonia, the conversion to polyamines or polythiols by catalytic hydrogenation in the presence of ammonia or hydrogen sulphide respectively, the conversion to polyphenols by condensation with phenols and the conversion to polyketals by reaction with alcohols. The applicant has carried out an investigation into the preparation of the present polymers with a low average molecular weight. Initially, it was tried by means of fractionation to separate a low molecular weight fraction from the material prepared in the conventional manner and having an average molecular weight of more than 10,000. Apart from the fact that this separation method is very time consuming, it produces the desired low molecular weight material in only a very low yield. Carrying out the polymerization at very high temperatures was also rejected as unattractive, since this manner of processing has a very unfavorable influence on the stability of the catalyst composition. In the course of continued research by the applicant into this subject it was investigated in how far the carrying out of the polymerization in the presence of hydrogen could lead to the desired goal. The initial results from the use of catalyst compositions containing a tetraarylbisphosphine as bidentate ligand were disappointing. Although it was possible in this way to achieve some reduction in the average molecular weight, the prepared polymers still possessed a M n which was considerably higher than 10,000. In the investigation, however, it was surprisingly found that the presence of hydrogen has a very strongly lowering effect on the average molecular weight of the prepared polymers if the polymerization is carried out using a catalyst composition containing a tetraalkylbisphosphine as bidentate ligand. In this way it was possible to prepare polymers with a M n of less than 2500 in a high yield. This result indeed unexpected in the light of EP-A-248483 which shows that, when using a tetraphenylbisphosphine as bidentate ligand, the presence of hydrogen leads to an increase of the molecular weight. The present invention therefore relates to a process for the preparation of polymers wherein polymers of carbon monoxide with ethene and/or propene and optionally in addition with one or more other α-olefins are prepared by contacting the monomers in the presence of hydrogen with a catalyst composition containing a Group VIII metal and a phosphorus bidentate ligand of the general formula R₅R₆P-R-PR₇R₈ in which R₅ to R₈ represent identical or different monovalent aliphatic hydrocarbon groups and R is a divalent organic bridging group containing at least two carbon atoms in the bridge connecting the two phosphorus atoms to each other. An additional reduction in the average molecular weight of the polymers can be achieved by additionally carrying out the polymerization in the presence of a compound of the general formula CH₂=C(R₃)-C(=O)X where R₃ represents hydrogen or an alkyl group and X a hydroxyl group, an alkoxy group or an optionally alkyl substituted amino group. By carrying out the polymerization in the presence of hydrogen and a compound of this type, polymers with a M n of less than 1000 can be prepared in a high yield. A very suitable compound for the present purpose is methylacrylate. The favourable effect of compounds of the general formula CH₂=C(R₃)-C(=O)X only occurs if the polymerization is carried out using a catalyst composition containing a tetraalkylbisphosphine and additionally in the presence of hydrogen. It was found that if the polymerization is carried out either using a catalyst composition containing a tetraalkylbisphosphine but in the absence of hydrogen, or in the presence of hydrogen but using a catalyst composition containing a tetraarylbisphosphine, the presence of the above-mentioned compounds has such an inhibiting influence on the polymerization that hardly any polymerization takes place. In the preparation of polymers of carbon monoxide with ethene and with one or more α-olefins having at least three carbon atoms per molecule (hereinafter referred to as C₃+ α-olefins for brevity) using catalyst compositions containing a Group VIII metal and a phosphorus bidentate ligand of the general formula R₁R₂P-R-PR₃R₄, polymers are obtained in which a proportion of the units from carbon monoxide occur in 2,5-furandiyl groups, which groups are substantially present as 3-alkyl-2,5-furandiyl groups. The more C₃+ α-olefins the prepared polymers contain, the higher the percentage of the units from carbon monoxide that are present in optionally 3-alkyl substituted 2,5-furandiyl groups. If the above-mentioned catalyst compositions are employed for the preparation of polymers of carbon monoxide with one or more C₃+ α-olefins (i.e. without ethene), polymers are obtained in which more than 10% of the units from carbon monoxide are present in 3-alkyl-2,5-furandiyl groups. In some cases, with these polymers as much as about 50% of the units from carbon monoxide can be present bonded in this way. The presence of a substantial percentage of the units from carbon monoxide in optionally 3-alkyl substituted furandiyl groups is undesirable for two reasons. Firstly it adversely affects the stability of the polymers. The second drawback is related to the possibility of chemical modification of the polymers via the carbonyl groups present therein. The higher the percentage of the units from carbon monoxide in optionally 3-alkyl substituted 2,5-furandiyl groups the lower the percentage of these units that are present as carbonyl groups. This limits the possibility of chemical modification of the polymers. During the investigation by the applicant it was found that if in the preparation of polymers of carbon monoxide with propene and optionally also with one or more other α-olefins the polymerization is carried out according to the invention in the presence of hydrogen and a catalyst composition containing a tetraalkylbisphosphine and additionally in the presence of a liquid diluent consisting substantially of one or more of the C₃+ α-olefins employed as monomers, not only are polymers with a low average molecular weight obtained, but, moreover, the furan formation is combated extremely effectively in this polymerization. The process of the invention is carried out in the presence of hydrogen. Preferably the polymerization takes place at a hydrogen partial pressure between 1 and 50 bar and in particular between 2 and 40 bar. In this invention, Group VIII metals are understood to be the noble metals ruthenium, rhodium, palladium, osmium, iridium and platinum, as well as the iron group metals iron, cobalt and nickel. In the catalyst compositions according to the invention the Group VIII metal is preferably selected from palladium, nickel and cobalt. Palladium is particularly preferred as Group VIII metal. The incorporation of the Group VIII metal in the catalyst compositions preferably takes place in the form of a salt of a carboxylic acid, in particular in the form of an acetate. In the phosphorus bidentate ligands of the general formula R₅R₆P-R-PR₇R₈ which are eligible for use in the catalyst compositions, the groups R₅ to R₈ preferably each contain not more than 6 carbon atoms. There is also preference for phosphorus bidentate ligands in which the groups R₅ to R₈ are the same as one another. Examples of suitable groups R₅ to R₈ are the methyl, the ethyl, the n-propyl and the n-butyl groups. As regards the bridging group R in the phosphorus bidentate ligands, there is preference for bridging groups containing three atoms in the bridge, of which at least two are carbon atoms. Examples of suitable bridging groups R are the -CH₂-CH₂-CH₂- group, the -CH₂-C(CH₃)₂-CH₂- group and the -CH₂-Si(CH₃)₂-CH₂- group. Worth mentioning as a very suitable phosphorus bidentate ligand is 1,3-bis(di n-butylphosphino)propane. The phosphorus bidentate ligands in the catalyst compositions are preferably used in a quantity of 0.5-2 and in particular 0.75-1.5 mol per g.atom Group VIII metal. In addition to a Group VIII metal and a phosphorus bidentate ligand, the catalyst compositions used in the polymer preparation according to the invention preferably also contain an anion of an acid with a pKa of less than 4 and in particular an anion of an acid with a pKa of less than 2. Examples of acids with a pKa of less than 2 are mineral acids such as perchloric acid, sulphonic acids such as para-toluenesulphonic acid and trifluoromethanesulphonic acid and halocarboxylic acids such as trifluoroacetic acid. There is preference for a sulphonic acid such as trifluoromethanesulphonic acid. The incorporation of the anion of an acid with a pKa of less than 4 in the catalyst composition can take place in the form of an acid and/or in the form of a salt. A nickel salt such as nickel perchlorate is very suitable as a salt. The anion is preferably present in the catalyst compositions in a quantity of 1-100 and in particular 2-50 mol per g.atom Group VIII metal. In addition to a Group VIII metal, a phosphorus bidentate ligand and optionally an anion of an acid with a pKa of less than 4, the catalyst compositions which are eligible for use in the polymer preparation according to the invention preferably also contain an organic oxidizing agent. Examples of suitable organic oxidizing agents are 1,2- and 1,4-quinones, aliphatic nitrites such as butyl nitrite and aromatic nitro compounds such as nitrobenzene and 2,4-dinitrotoluene. 1,4-quinones are preferred, and in particular 1,4-benzoquinone and 1,4-naphthoquinone. The organic oxidizing agent is preferably present in the catalyst compositions in a quantity of 5-5000 and in particular 10-1000 mol per g.atom Group VIII metal. If the process of the invention is employed for the preparation of polymers of carbon monoxide with ethene and/or propene and also with one or more other α-olefins, the latter α-olefins preferably contain fewer than 10 carbon atoms per molecule. The process of the invention is particularly important for the preparation of polymers of carbon monoxide with ethene and/or propene. The preparation of the polymers according to the invention is preferably carried out in the presence of a liquid diluent. Polar liquids are preferably used as diluents. These liquids can be protic or aprotic. An example of a suitable protic liquid is methanol. Examples of suitable aprotic liquids are acetone and tetrahydrofuran. If desired, the polymerization can also be carried out in the gas phase. If in the preparation of polymers of carbon monoxide with propene and optionally also with one or more other α-olefins it is intended to minimize the furan formation, the polymerization should be carried out in the presence of a liquid diluent consisting substantially of one or more of the C₃+ α-olefins employed as monomers. The polymer preparation can be carried out either batchwise or continuously. The quantity of catalyst composition used in the preparation of the polymers can vary within wide limits. Per mol of olefinically unsaturated compound to be polymerized a quantity of catalyst composition is preferably used which contains 10⁻⁷-10⁻³ and in particular 10⁻⁶-10⁻⁴ g.atom Group VIII metal. The preparation of the polymers is preferably carried out at a temperature of 20-150°C and a pressure of 2-150 bar and in particular at a temperature of 30-130°C and a pressure of 5-100 bar. The molar ratio of the olefinically unsaturated compounds relative to carbon monoxide is preferably 10:1-1:10 and in particular 5:1-1:5. The invention will now be illustrated with reference to the following examples: Example 1 A carbon monoxide/ethene copolymer was prepared as follows. Into a stirred autoclave with a volume of 250 ml a catalyst solution was introduced consisting of: 40 ml tetrahydrofuran, 0.1 mmol palladium acetate, 0.3 mmol trifluoromethanesulphonic acid, and 0.2 mmol 1,3-bis(di n-butylphosphino)propane. After successively forcing in 25 bar carbon monoxide, 25 bar hydrogen and 20 bar ethene, the autoclave contents were brought to 80°C. After 5 hours the polymerization was terminated by cooling the reaction mixture to room temperature and releasing the pressure. The polymer was filtered off, washed with methanol and dried. 10.5 g copolymer with a M n of 1400 was obtained. Example 2 A carbon monoxide/ethene copolymer was prepared in substantially the same way as in example 1, but with the difference that in addition 30 ml methylacrylate was introduced into the autoclave. 7.5 g copolymer with a M n of 350 was obtained. Example 3 Example 2 was substantially repeated, but with the difference that no hydrogen was forced into the autoclave. Only a trace of polymer material was obtained. Example 4 Example 2 was substantially repeated, but with the difference that the catalyst solution contained 0.2 mmol 1,3-bis(diphenylphosphino)propane instead of 1,3-bis(di n-butylphosphino)propane. Only a trace of polymer material was obtained. Example 5 A carbon monoxide/ethene copolymer was prepared in substantially the same way as in example 1, but with the difference that the catalyst solution contained 0.2 mmol 1,3-bis(diphenylphosphino) propane instead of 1,3-bis(di n-butylphosphino)propane. 7 g copolymer with a M n >20,000 was obtained. Example 6 A carbon monoxide/propene copolymer was prepared as follows. Into a stirred autoclave with a volume of 300 ml and from which air had been driven by purging with nitrogen, a catalyst solution was introduced consisting of: 120 ml methanol, 0.10 mmol palladium acetate, 0.11 mmol 1,3-bis(diphenylphosphino)propane, and 0.2 mmol para-toluenesulphonic acid. After adding 26 g propene, the autoclave contents were brought to 60°C and carbon monoxide was then forced in until a pressure of 40 bar was reached. During the polymerization the pressure was kept constant by forcing in carbon monoxide. After 1 hour the polymerization was terminated by cooling the reaction mixture to room temperature and releasing the pressure. The polymer was isolated by evaporating down the reaction mixture. 6.9 g copolymer was obtained. The degree of furanization was 24%. Example 7 A carbon monoxide/propene copolymer was prepared as follows. Into a stirred autoclave with a volume of 100 ml and from which air had been driven by purging with nitrogen, a catalyst solution was introduced consisting of: 40 ml methanol, 0.05 mmol palladium acetate, 0.055 mmol 1,4-bis(di n butylphosphino)butane, and 0.1 mmol para-toluenesulphonic acid. After adding 12.1 g propene, the autoclave contents were brought to 80°C and carbon monoxide was then forced in until a pressure of 40 bar was reached. During the polymerization the pressure was kept constant by forcing in carbon monoxide. After 1 hour the polymerization was terminated by cooling the reaction mixture to room temperature and releasing the pressure. The polymer was isolated by evaporating down the reaction mixture. 1.0 g copolymer was obtained. The degree of furanization was 25%. Example 8 A carbon monoxide/propene copolymer was prepared as follows. 200 ml propene was introduced into a stirred autoclave with a volume of 300 ml. After the autoclave contents had been brought to 80°C carbon monoxide was forced in until a pressure of 50 bar was reached and then hydrogen until a pressure of 55 bar was reached. A catalyst solution was then introduced into the autoclave consisting of: 4 ml acetone, 0.02 mmol palladium acetate, 0.1 mmol nickel perchlorate, and 0.024 mmol 1,3-bis(di n-butylphosphino)propane. During the polymerization the pressure was kept constant by forcing in carbon monoxide. After 12 hours the polymerization was terminated by cooling the reaction mixture to room temperature and releasing the pressure. The polymer was isolated by evaporating down the reaction mixture. 3.7 g copolymer was obtained with a M n of 910. The degree of furanization was less than 1%. Example 9 A carbon monoxide/propene copolymer was prepared in substantially the same way as in example 8, but with the following differences: a) carbon monoxide was forced into the autoclave until a pressure of 55 bar was reached instead of 50 bar and then hydrogen to a pressure of 58 bar instead of 55 bar. b) the catalyst solution additionally contained 7 ml n-pentane, and c) the reaction time was 16 hours instead of 12 hours. 13.4 g copolymer was obtained with a M n of 1260. The degree of furanization was less than 1%. Example 10 A carbon monoxide/ethene/propene terpolymer was prepared in substantially the same way as the carbon monoxide/propene copolymer in example 8, but with the following differences: a) the reaction temperature was 75°C instead of 80°C, b) a 1:1 carbon monoxide/ethene mixture was forced into the autoclave until a pressure of 55 bar was reached instead of carbon monoxide to a pressure of 50 bar and then hydrogen to a pressure of 59 bar instead of 55 bar. c) the catalyst solution additionally contained 7 ml n-pentane, and d) the reaction time was 18 hours instead of 12 hours. 10.5 g terpolymer was obtained with a M n of 1350. The degree of furanization was less than 1%. Of the examples 1-10, examples 1, 2 and 8-10 are according to the invention. According to these examples, in the presence of hydrogen and using catalyst compositions containing a tetraalkylbisphosphine as phosphorus bidentate ligand, polymers of carbon monoxide with ethene and/or propene were prepared with a M n <2500. Examples 3-7 fall outside the scope of the invention and have been included in the patent application for comparison. Examples 3 and 4 demonstrate the inhibiting effect of methylacrylate on the polymer formation if the polymerization is carried out either using a catalyst composition containing a tetraalkylbisphosphine but in the absence of hydrogen, or in the presence of hydrogen but using a catalyst composition containing a tetraarylbisphosphine. Example 5 shows that if the polymerization is carried out using a catalyst composition containing a tetraarylbisphosphine, polymers with a very high average molecular weight are obtained and this despite the fact that the polymerization is carried out in the presence of hydrogen. Examples 6 and 7 demonstrate the high degree of furanization, both when using a catalyst composition containing a tetraalkylbisphosphine and when using a catalyst composition containing a tetraarylbisphosphine, if the polymerization is carried out in methanol as diluent. The degree of furanization is understood in this patent application as the number of units from carbon monoxide present in optionally 3-alkyl-substituted 2,5-furandiyl groups as a percentage of the total number of units from carbon monoxide that are present in the polymers. The degree of furanization was determined with the aid of NMR analysis. The lowering influence on the average molecular weight of the polymers which occurs if the polymerization according to the invention is carried out in the presence of methylacrylate can be seen by comparison of the results of examples 1 and 2. The results of examples 8-10 demonstrate the low degree of furanization which occurs if the polymerization according to the invention is carried out in liquid propene as diluent. It was established by NMR analysis that the polymers prepared according to examples 1, 2 and 5-10 were built up from linear chains in which the units from carbon monoxide on the one hand and the units from the olefins on the other hand occurred in an alternating arrangement. In the polymers prepared according to example 10 the units from ethene and propene were present in a random arrangement relative to one another.

Claims: Process for the preparation of polymers, characterized in that polymers of carbon monoxide with ethene and/or propene and optionally in addition with one or more other α-olefins are prepared by contacting the monomers in the presence of hydrogen with a catalyst composition containing a Group VIII metal and a phosphorus bidentate ligand of the general formula R₅R₆P-R-PR₇R₈ in which R₅ to R₈ represent identical or different monovalent aliphatic hydrocarbon groups and R is a divalent organic bridging group containing at least two carbon atoms in the bridge connecting the two phosphorus atoms to each other. Process according to claim 1, characterized in that it is carried out at a hydrogen partial pressure between 2 and 40 bar. Process according to claim 1 or 2, characterized in that it is carried out in the presence of a compound of the general formula CH₂=C(R₃)-C(=0)X where R₃ represents hydrogen or an alkyl group and X a hydroxyl group, an alkoxy group or an optionally alkyl substituted amino group. Process according to claim 3, characterized in that it is carried out in the presence of methylacrylate. Process according to one or more of claims 1-4, characterized in that the Group VIII metal is incorporated in the catalyst composition in the form of a salt of a carboxylic acid such as an acetate. Process according to one or more of claims 1-5, characterized in that the groups R₅ to R₈ in the phosphorus bidentate ligand each contain not more than 6 carbon atoms. Process according to one or more of claims 1-6, characterized in that the bridging group R in the phosphorus bidentate ligand contains three atoms in the bridge, of which at least two are carbon atoms. Process according to claim 7, characterized in that the catalyst composition contains 1,3-bis(di n-butylphosphino)propane as phosphorus bidentate ligand. Process according to one or more of claims 1-8, characterized in that the catalyst composition additionally contains an anion of an acid with a pKa of less than 4 or less than 2. Process according to any one of claims 1 to 9, characterized in that the catalyst composition additionally contains a 1,4-quinone such as 1,4-benzoquinone or 1,4-naphthoquinone. Process according to any one of claims 1-10, characterized in that if it is applied for the preparation of polymers of carbon monoxide with ethene and/or propene and in addition with one or more other α-olefins, the latter α-olefins contain fewer than 10 carbon atoms.

Inventors: DRENT EIT, KEIJSPER JOHANNES JACOBUS, DRENT, EIT, KEIJSPER, JOHANNES JACOBUS
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1992
Main classification: C08G67
IPC codes: C08G67