The invention relates to a process for producing a polymer composition by hydrogenating an unsaturated polymer, comprising the reaction of an unsaturated polymer with hydrogen in the presence of a supported metal catalyst. The invention additionally relates to a polymer composition produced by the process according to the invention, and also to the use of a polymer composition for producing comb polymers. For the purposes of this invention, unsaturated polymers are to be understood as meaning organic polymers having at least one carbon-carbon double or triple bond. An example of such a polymer is polybutadiene. Unsaturated polymers are used industrially in a wide variety of fields, for example in tyre production or for improving the mechanical properties of various plastics.

A disadvantage of unsaturated polymers is their high susceptibility to oxidative degradation which is promoted for example by UV radiation or chemical influences. This susceptibility stems from the high reactivity of the unsaturated carbon-carbon bond.

In order to avoid this disadvantage, unsaturated polymers are often catalytically hydrogenated in order to saturate the carbon-carbon bonds. The saturated polymers obtained are highly stable and undergo only minor, if any, discolouration and decomposition at higher temperatures. Furthermore, these polymers are highly resistant to weathering and oxidation and also are also highly lightfast. In addition, the physical properties such as, for example, elongation or tensile strength are stable even over prolonged periods.

The hydrogenation is typically carried out in the presence of a metal catalyst. Either a homogeneous catalyst or a heterogeneous catalyst may be used therein. Normally in industrial processes, a heterogeneously catalysed reaction is preferable since it offers advantages in terms of catalyst recovery and is therefore cheaper. Additionally, the simpler catalyst recovery also facilitates product purification. However, in the case of polymer hydrogenation, difficulties often arise due to the combination of high molecular weight polymers with solid catalysts, since the high molecular weight polymers cannot penetrate into the pore system of the catalyst. This often results in a reduction in catalyst activity.

This disadvantage is avoided with homogeneous catalysis, where the catalyst is dissolved in a solvent together with the polymer and leads to significantly higher activities on account of the increased mobility. Thus, DE 1920403 for example describes the selective hydrogenation of olefinic double bonds in hydrocarbon polymers using a homogeneous three-component catalyst.

Processes for heterogeneously catalysed hydrogenation intended to avoid the disadvantages mentioned are likewise known. German laid-open specification DE 24591 15 describes a process for

hydrogenating unsaturated polyhydroxyhydrocarbons in the presence of a supported ruthenium catalyst.

Japanese publication JP 54-40897 describes a process for hydrogenating carbon- carbon double bonds in a polymer using a metal catalyst applied to a porous carbon support.

German laid-open specification DE 2845615 describes a process for

hydrogenating polymers in the presence of a heterogeneous metal catalyst applied to a porous support.

Japanese publication JP 57-202305 describes a process for hydrogenating a conjugated diene polymer using a carbon-supported catalyst. German laid-open specification DE 10 2005 031 244 A1 describes oil-soluble comb polymers, methods for their preparation and their use in lubricating oil compositions. In said document, no mention is made to prepare the polymers by hydrogenating an unsaturated polymer. British laid-open specification GB 2 270 31 17 A describes the manufacture of low viscosity hydrogenated butadiene polymers having terminal functional groups and the use of the low viscosity polymers to make coatings and other high molecular weight polymers. GB 2 270 31 17 A does not disclose hydrogenation to be carried out in the presence of a supported metal catalyst having a specific pore size distribution.

International laid-open specification WO 01/42319 A1 describes a hydrogenation catalyst and a process for hydrogenating an unsaturated polymer comprising contacting the unsaturated polymer with a hydrogenating agent in the presence of a mixed hydrogenation catalyst, characterized in that the mixed hydrogenation catalyst comprises a Group VIII metal component and at least one component selected from the group consisting of a rhenium, molybdenum, tungsten, tantalum and niobium component. WO 01/42319 A1 discloses a supported metal catalyst having a narrow pore size distribution. However, supported metal catalysts having this narrow pore size distribution are not sufficient to achieve the advantageous results achievable with the catalysts used in the present invention. M. Shirai et al describe in "Applied Catalysis A: General", Elsevier Science,

Amsterdam, NL, Bd. 177, Nr. 2, 1999, 219-225, the size-selective hydrogenation of butadiene-acrylonitrile rubbers (NBR) in carbon tetrachloride using palladium particles dispersed in pores of different sizes. However, said catalysts disclosed in this literature are not sufficient to overcome the problem of reduction in catalyst activity.

M. Schellekens et al describe in "Macromolecular Chemistry and Physics", Wiley- VCH Verlag, Weinheim, Bd. 202, Nr. 9, 2001 , 1595-1601 , the synthesis of poly(ethylene-co-ethylene)-block-poly(methyl methacrylate) by atom transfer radical polymerization. It is not described that the polymer is prepared by hydrogenating an unsaturated polymer. U. Schubert describes in "Physik in unserer Zeit", Bd. 18, Nr. 5, 1987, 137-143, new developments regarding metal catalysts.

However, in view of the previously-mentioned prior art documents, there is still a need to investigate further on the calatytic hydrogenation conditions of

unsaturated polymers and in particular on new catalysts to improve the results obtained by hydrogenating unsaturated polymers. Indeed, a common

disadvantage in the catalytic hydrogenation of unsaturated polymers is the occurrence of undesired side reactions. These include for example the elimination of functional groups bonded to the polymer. This problem occurs particularly with hydroxylated polybutadiene. A further undesired side reaction is crosslinking via carbon-carbon coupling of the polymers to be hydrogenated. These

disadvantages are only inadequately avoided by known processes for

heterogeneously catalysed hydrogenation, including all of the above-mentioned patent and non-patent literature.

Thus, it is an object of the present invention to provide a heterogeneously catalysed process for hydrogenating unsaturated polymers, in which the hydrogenation proceeds with a sufficiently high rate and yield, while avoiding any side reactions, such as the elimination of functional groups and carbon-carbon coupling between individual polymer molecules.

This object is achieved by the present claimed process for producing a polymer composition by hydrogenating an unsaturated polymer, comprising the reaction of an unsaturated polymer with hydrogen in the presence of a supported metal catalyst which comprises a porous solid as the support and a catalytically active metal deposited on the support, characterized in that the unsaturated polymer has a weight-average molecular weight of 3000 to 10000 g/mol and 45 to 65% of the pore volume of the support is formed from macropores having a pore diameter of more than 50 nm and 35 to 55% of the pore volume of the support is formed from mesopores having a pore diameter of 2 to 50 nm. The catalyst used in accordance with the invention comprises a porous support material which is characterized by a particular pore distribution. Without wishing to be bound to this theory it is believed that the inventive combination of a support material having a particular pore distribution and an unsaturated polymer having a weight-average molecular weight of 3000 to 10 000 g/mol ensures that the polymer can penetrate to the catalytically active metal disposed in the pores of the support. In this way the catalyst appears to be optimally utilized, which leads to a high reaction rate and yield. At the same time, undesired side reactions, like in particular crosslinking of the polymers and elimination of functional groups, are minimized.

The determination of the pore distribution is effected by mercury porosimetry according to DIN 66133. For the purposes of this invention the pore distribution describes the percentage of the pore volume accounted for by pores of a particular size. In the determination of pore distribution a distinction is made between macropores, which have a pore diameter greater than 50 nm,

mesopores, which have a pore diameter of 2 to 50 nm, and micropores, which have a pore diameter smaller than 2 nm, in accordance with the lUPAC definition. The pore distribution is reported using the percentage of the pore volume accounted for by macropores, mesopores and/or micropores.

The diameter of the macropores is preferably in the range 50 to 50 000 nm, particularly in the range 50 to 10 000 nm. The fraction of macropores preferably amounts to 50 to 60% of the pore volume, more preferably 52 to 58%. The fraction of mesopores preferably amounts to 40 to 50% of the pore volume, more preferably 42 to 48%. In particularly preferred supports, the fraction of macropores amounts to 52 to 58% of the pore volume and the fraction of mesopores amounts to 42 to 48% of the pore volume.

Micropores, if present, are generally present only in an amount of less than 10%, preferably less than 1 %, of the pore volume. The modification of the support may be uniform or mixed, and so the pore distribution may be monomodal, bimodal or trimodal.

The total pore volume is preferably 0.1 to 1 .5 ml/g, more preferably 0.5 to 1 ml/g, in particular 0.7 to 0.8 ml/g.

In a preferred embodiment of the invention the catalyst exhibits, in addition to the pore distribution mentioned above, a specific BET surface area according to DIN 66131 in the region of greater than 30 m ² /g. The specific BET surface is

preferably in the range of 40 to 70 m ² /g, even more preferably 45 to 65 m ² /g.

Oxides of the series AI ₂ O ₃ , TiO ₂ , ZrO ₂ , SiO ₂ , MgO, ZnO und MgAI ₂ O ₄ are examples of support materials used. The use of AI ₂ O3 and TiO ₂ has proven to be particularly preferable.

The catalyst comprises a catalytically active metal deposited on the support.

Metals useful for catalysing hydrogenation reactions are known in the prior art. By way of example, the following catalytic metals may be used: Ru, Rh, Pd, Ir, Pt, Mn, Cr, Fe, Co, Ni, U, Cu, Nd, In, Sn, Zn, Ag, Cr and alloys of one or more of these metals.

In a preferred embodiment, the catalytically active metal is Ru, Pd or a mixture of Ru and/or Pd with at least one further metal, wherein the at least one further metal is selected from the group consisting of Cu, Ag, Au, Mn, Re, Fe, Co, Ni, Rh, Os, Ir, Pt or any desired combinations thereof.

The combination of ruthenium or palladium with AI ₂ O ₃ as the support material has proven particularly advantageous. It has become apparent that the use of such catalysts particularly in the hydrogenation of polybutadiene and monohydroxylated polybutadiene leads to a reduction in undesired side reactions.

The supported catalysts to be used according to the invention may be industrially produced by depositing the catalytically active metal to the support. Application may be achieved by spraying of aqueous metal salt solutions onto the support or by other processes. Useful metal salts include, for example, ruthenium nitrate or palladium nitrate. The supports impregnated with a metal salt are dried, preferably at temperatures of 100 to 150°C, and optionally calcined at temperatures of 200 to 600°C. The impregnated supports are subsequently activated by treatment of the impregnated supports in a gas stream containing free hydrogen, at temperatures of 30 to 600°C, preferably of 150 to 400°C. The gas stream preferably consists of a mixture of hydrogen and nitrogen, being the volume of hydrogen of less than 10% by volume, even more preferably of less than 5% by volume, based on the total volume of the hydrogen/nitrogen gas mixture.

The metal salt solution is applied to the support in an amount such that the finished catalyst comprises 0.01 to 20 wt% of catalytically active metal based on the total weight of the catalyst. The fraction of catalytically active metal preferably amounts to 0.2 to 15 wt%, more preferably 0.2 to 5 wt%, based on the total weight of the catalyst. According to a preferred embodiment the impregnation of the support is effected by spray application of a metal salt solution at elevated temperature, in particular above 50°C and more preferably at 80 to 150°C, so that the solvent already at least partially evaporates during spraying and the penetration depth of the catalytically active metals is limited. A catalyst produced in this manner is also described as a shell catalyst in the context of this invention. The penetration depth is preferably in the range from 25 to 250 μιτι, more preferably 25 to 150 μιτι and most preferably 50 to 120 μιτι. The penetration depth can be determined with the aid of light micrographs. The polymers to be used according to the invention have a weight-average molecular weight of 3000 to 10 000 g/mol, preferably of 3000 to 8000 g/mol, more preferably of 4000 to 8000 g/mol and most preferably of 4000 to 5000 g/mol. The weight-average molecular weight of the polymers is determined by gel permeation chromatography according to DIN 55672-1 .

In a preferred embodiment, the polymers exhibit a narrow molecular weight distribution. This can be verified by reference to the polydispersity index (PDI) determined by means of gel permeation chromatography according to DIN 55672- 1 . The PDI here refers to the ratio of weight-average and number-average molecular weight. It is preferred that the polymers have a PDI less than 2, more preferably less than 1 .5, in particular less than 1 .1 .

The unsaturated polymer to be used according to the invention is characterized in that it comprises one or more carbon-carbon double and/or triple bonds. The unsaturated polymer is preferably a polymer based on dienes. For the purposes of this invention these are to be understood as meaning polymers obtained via polymerization of conjugated dienes or via copolymerization of conjugated dienes with copolymerizable unsaturated compounds, e.g. phenyl-substituted aromatic hydrocarbons.

Useful polymerizable dienes include, for example, 1 ,3-butadiene, 1 ,3-pentadiene, 2,3-dimethylbutadiene, phenylbutadiene or isoprene.

Examples of useful unsaturated polymers based on dienes include polybutadiene, polyisoprene, butadiene-styrene copolymers, butadiene-alpha-methylstyrene copolymers, butadiene-isoprene copolymers, butadiene-acrylonitrile copolymers and butadiene-phenylpyridine copolymers.

In addition, the polymers to be used according to the invention may have been functionalized. For the purposes of the present invention functional ized polymers are to be understood as meaning polymers modified with at least one functional group. Particular preference is given to terminal functional groups. A terminal functional group is to be understood as meaning a functional group joined to the first or second carbon atom, counted from one end of the polymer molecule. Useful functional groups include, for example, hydroxyl groups, carboxyl groups, amino groups, thiol groups and halogen atoms.

The process according to the invention is particularly useful for hydrogenating monofunctionalized unsaturated polymers. For the purposes of this invention, monofunctionalized polymers are to be understood as meaning polymers comprising on average 0.8 to 1 .2 functional groups per polymer molecule. The hydrogenation of such polymers is particularly challenging because a large number of completely non-functionalized products is easily formed via potential elimination reactions. Elimination reactions thus have a significantly greater effect on the composition of the product than they do with polyfunctionalized polymers. Additionally, chain lengthening through the C-C coupling of two polymer chains may occur. This leads firstly to a broadening of the molar mass distribution and, more seriously in the case of monofunctionalized polymers, to an increase in the functionality of these coupled chains from one to two. In this way, the polymer is converted from a chain terminator to a crosslinker. However, these disadvantages are minimized by the process according to the invention.

The process according to the invention particularly relates to the use of monohydroxylated polymers based on dienes. For the purposes of this invention, monohydroxylated polymers are to be understood as meaning polymers comprising on average 0.8 to 1 .2, preferably 0.9 to 1 .05, hydroxyl groups per polymer molecule. The mean number of hydroxyl groups is determined by ¹ H NMR by reference to the integral of the signal of the CH ₂ group in the a position to the OH group. The process according to the invention has proven particularly preferable for the hydrogenation of monohydroxylated polybutadiene.

The OH functionality is determined by means of ¹ H NMR. In the ¹ H spectrum, the shift of the CH ₂ group in the alpha position to the OH group can be clearly distinguished from all other shifts of aliphatic and olefinic protons. The average OH functionality is determined in this way. In the case of polybutadiene or functionalized polybutadiene, the polybutadiene may have both 1 ,4 linkages and 1 ,2 linkages. Typically, both 1 ,4 linkages and 1 ,2 linkages occur in a molecule. The ratio of 1 ,2 linkages to 1 ,4 linkages is preferably in the range from 1 :100 to 100:1 , more preferably in the range from 2:3 to 1 :3. The process according to the invention may nevertheless also be applied to

polybutadienes having exclusively 1 ,2 linkages or 1 ,4 linkages.

The unsaturated polymers to be used according to the invention are produced are via processes which are known per se. For example, the production of

unsaturated polymers based on dienes may be effected by anionic polymerization of dienes. The production of functionalized unsaturated polymers based on dienes may be effected by anionic polymerization of dienes and subsequent reaction of the polymers with an alkylene oxide, for example ethylene oxide or propylene oxide, and finally reaction with a protic acid.

A process for producing functionalized unsaturated polymers based on dienes and useful for the process according to the invention is described in European laid-open specification EP 0 344 888 A2. In the reaction of the unsaturated polymer with hydrogen, the unsaturated polymer may be present in the form of an undiluted liquid or in solution. Possible solvents are aliphatic hydrocarbons such as, for example, hexane, heptane, octane, cyclohexane and methylcyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; alcohols, such as n-propyl alcohol, isopropyl alcohol and n- butyl alcohol; ethers, such as diethyl ether, dipropyl ether and tetrahydrofuran; esters, such as ethyl acetate and butyl acetate; water and mixtures of the solvents mentioned.

Particularly in the hydrogenation of polybutadiene or functionalized polybutadiene, the use of cyclohexane, hexane, heptane or pentane as solvent is particularly preferred. If a solvent is used, the concentration of the unsaturated polymer is preferably 10 to 70 wt%.

The reaction temperature in the reaction of the unsaturated polymer and hydrogen is preferably in the range from 20 to 200°C, more preferably 50 to 200°C and most preferably 50 to 150°C.

The hydrogen may be injected under atmospheric or elevated pressure. The hydrogen pressure is preferably 15 to 500 bar, more preferably 50 to 300 bar and most preferably 100 to 250 bar.

The process may be operated continuously or batchwise.

Since the process according to the invention is a heterogeneously catalysed reaction, the catalyst may for example be supported in the reactor space in solid form on a screen and thus may be easily removed from the reaction mixture once the reaction has ended. The solvent may for example be removed by distillation. This procedure has the advantage that the product generally need not be purified any further. Minor impurities such as for example abraded reactor material or catalyst residues can be removed in a simple manner via a filtration step.

The invention also relates to the use of a polymer composition for producing comb polymers, wherein the polymer composition is produced via the process described above.

For the purposes of this invention, a comb polymer comprises a first polymer, also described as a backbone or main chain, and a plurality of further polymers which are described as side chains and are covalently bonded to the backbone. The covalent bonds between the backbone and the side chains may, for example, be ester bonds, ether bonds, amide bonds, thioether bonds, thioester bonds or carbon-carbon bonds. The polymer composition to be used according to the invention preferably forms the side chains of the comb polymer.

In a particularly preferred embodiment the polymer composition to be used is produced by the process described above, wherein the unsaturated polymer used in the process described above is modified with at least one functional group.

The polymer composition to be used thus preferably comprises functionalized polymers. The polymer composition to be used more preferably comprises monohydroxylated polymers, in which case the polymer composition is produced from monohydroxylated polybutadiene via the process described above. These polymer compositions produced by the process described above have the decisive advantage that they exhibit a large proportion of monofunctionalized polymers and a small proportion of polyfunctionalized polymers. Undesired crossl inking reactions during synthesis of the comb polymers are thus avoided.

Examples

Example 1

A 2 I autoclave with catalyst basket and stirring means according to the Robinson- Mahoney method is charged with 1000 g of 50 wt% monofunctional, OH-terminated polybutadiene (weight-average molecular weight 4500 g/mol; polydispersity index 1 .04, ratio of 1 ,2 linkages to 1 ,4 linkages 63:37 by ¹ H NMR, OH functionality 0.99 by ¹ H NMR) in cyclohexane. 80 g of a 3% Ru/AI ₂ O ₃ shell catalyst (55% macropores, 45% mesopores by mercury porosimetry according to DIN 66133) are introduced.

Hydrogenation is carried out for 22 h at H ₂ pressure 200 bar and 130°C.

The degree of hydrogenation and the OH functionality are examined by means of ¹ H NMR. By-product formation (dimerization and trimerization by C-C coupling) is determined by reference to the signals of the dimers and trimers in the molecular weight distribution determined by gel permeation chromatography according to DIN 55672-1 . The PDI is determined by gel permeation chromatography according to DIN 55672-1 (measured against polystyrene standards).

Method: gel permeation chromatography according to AN-SAA 0629

Eluent: tetrahydrofuran (THF)

Column combination: 600 x 8 mm; 5 μιτι, 50 A styrene-divinyl benzene copolymer

600 x 8 mm; 5 μιτι, 100 A styrene-divinyl benzene copolymer 600 x 8 mm; 5 μιτι, 500 A styrene-divinyl benzene copolymer

Injection volume: 100 μΙ

Flow rate: 1 ml/min

Detection: differential refractometer

Column temperature: room temperature

Calibration: polystyrene from 266 g/mol to 67 500 g/mol

Internal standard: ethylbenzene (0.5 g/l)

No suitable calibration standards were available for the polybutadienes used, in order to allow an absolute determination of the molar mass by means of GPC. Therefore, only the PDI from the GPC was used in order to observe chain lengthening by C-C coupling. The absolute molar mass was determined by means of NMR. The position of the CH ₃ group at the non-functionalized end of the chain (5(CH ₃ ) = 0.9 ppm) can be identified in the ¹ H NMR. All other CH signals are in the range of 1 .0-2.4 ppm

(aliphatic) and 4.7-6.0 ppm.

Example 2:

As per example 1 , except that in this case 80 g of a shell catalyst with 0.5% Pd/AI ₂ O3 (55% macropores, 45% mesopores) were used. The support material is identical to the material used in example 1 .

Example 3: In a batchwise circulation reactor with a 700 ml catalyst bed were installed 420 g of the 3% RU/AI2O3 shell catalyst (cf. Example 1 ). The reactant solution (4 kg of the polymer solution from Example 1 ) was passed over the catalyst with a circulation rate of 100 kg/h at hydrogenation pressure 200 bar and 130°C. Example 4:

A continuously operated trickle bed reactor (reactor volume 200 ml) was charged with 62 g of the catalyst from Examples 1 and 3. The reactor at 200 bar and 140°C was fed with the 50% polymer solution (see Examples 1 , 2 and 3) which had already been pre- hydrogenated to a degree of 85.6%. At an LHSV (liquid hourly space velocity) of 1 m ³ /(m ^2* h), the degree of hydrogenation at the end of the reactor was 99.7%. The OH functionality was 0.98 and the dimer content was <0.1 %. Comparative Example 1 :

As per Example 1 , except that in this case 80 g of a shell catalyst with 0.5% Pd/AI ₂ O3 (68% macropores, 32% mesopores) were used.

Comparative Example 2:

As per Example 1 , except that in this case 5 g of a 5% Pd/C powder catalyst

(palladium on activated charcoal, Aldrich no. 75992) were used. The catalyst basket was not used in this experiment and was removed from the autoclave.

The results of the examples and comparative examples are reproduced in Table 1.

Table 1 : Results (degree of hydrogenation, dimer content and OH functionality of the product) of the Examples and Comparative Examples

As shown with Comparative Example 1 in Table 1 , in case the amount of macropores of the metal supported catalyst is too high, not only activity

decreases, but also selectivity, which is unexpected.

From Comparative Example 2, it can be derived that using a powder catalyst, which is highly microporous, high activity can be achieved.

However, it has been unexpectedly observed that high selectivity, while

maintaining an excellent activity, can only be reached if the inventive catalyst support of the present invention is used in the hydrogenation process as shown in Examples 1 to 3.