MXPA97004619A - Procedure for the production of cauchoshidrogena - Google Patents

Abstract

The present invention relates to a process for the production of hydrogenated rubbers characterized by: A. solution polymerization of one or more monomers in the presence of an alkyl lithium to produce polymers or copolymers of conjugated dienes; B. addition to the reaction mixture of a compound selected from the following classes: R-OH, R-COOH, R'n-Si-Cl4-n, R'n-Sn-Cl4-n, where n is between 0 and 3, both inclusive, in an amount of equivalents that is at least equal to the amount of polymerization catalyst, where R is a C2-C20 alkyl group optionally containing one or more polar functional groups selected from C-OH, COOH and such that the compound has a ratio of solubilities between water and hydrogenation solvent greater than 49 and / or a boiling point greater than 110 ° C; R 'is a C1-C20 alkyl group or a C6-C20 aryl group;; C. hydrogenation of the deactivated polymer by adding a hydrogenation catalyst to the mixture and maintaining the mixture under hydrogen pressure in a continuous, discontinuous or batchwise manner using stirred reactors, tubular reactors or

Description

PROCEDURE FOR THE PRODUCTION OF HYDROGENED RUBBER The present invention relates to a process for the production of hydrogenated rubbers. More particularly, it relates to a process for the production of hydrogenated rubbers which allows an easy and effective deactivation of the living polymer before the hydrogenation step.

STATE OF ART Polymers containing olefinic double bonds are very common in the rubber industry. The presence of unsaturations allows the vulcanization of the polymer, but reduces resistance to aging and oxidation. Therefore, rubbers are frequently hydrogenated. The process for the production of hydrogenated rubbers is commonly carried out according to the following procedure: * polymerization of the monomers by known polymerization methods, such as anide polymerization, cationic polymerization, coordination polymerization, radical polymerization, etc. . good in -emulsion, solution or mass processes; * the polymer obtained is treated with water to deactivate the catalyst and purify the polymer while the solvent evaporates; * the polymer is dried and dissolved in an inert solvent in which it is hydrogenated using a suitable catalyst. This method produces a very good quality of the polymer but is very expensive. In fact it requires the evaporation of the solvent used in the polymerization and the polymer, before the hydrogenation, requires a careful stage of drying. As the solvent used in the polymerization can also be used in the hydrogenation, it has been proposed to make the -hydrogenation on the living polymer (U.S. Patent No. 4501857). However, this method has the disadvantage that the polymer, being still reactive, can continue to polymerize under uncontrolled conditions and can undergo secondary reactions that worsen the quality of the final product. In addition, the viscosity of the living polymer is quite high and requires a high energy consumption. It has also been proposed to deactivate the polymer - I live by reaction with hydrogen U.S. 5039755 and E.P. 0549063). The disadvantages of this method are the time required for the complete reaction with hydrogen, it is said to be 20 minutes, and the need to adjust the amount of LiH formed, too small for high molecular weights and too large for weights. low molecular Applicants have surprisingly found that it is possible to obtain a hydrogenated polymer which has very good properties and, at the same time, considerably reduce the process costs, with a simple catalytic system.

DESCRIPTION OF THE INVENTION The process of the present invention is characterized by the following steps: a) polymerization in solution of the monomers in the presence of an alkyl lithium to produce Cco) polymers of conjugated dienes. b) addition to the reaction mixture of a deactivating agent selected from the following classes: R-OH, R-COOH, R'n-Si-Cl4.-n, R'n-Sn-Cl4.-n, with n comprised between 0 and 3, both inclusive, in an amount of equivalents that is at least equal to the amount of polymerization catalyst, wherein R is a C-C- alkyl group which may optionally contain one or more polar functional groups selected from C-OH, COOH, and such that the compound has a solubility ratio in water and in the hydrogenated solvent greater than 49, and / or that the boiling point is greater than 110 ° C; R 'is an alkyl group c? ~ C2or an aryl group cg-c20; c) hydrogenation of the deactivated polymer by adding a hydrogenation catalyst to the mixture and maintaining the mixture under continuous pressure of hydrogen; discon tinuously or by means of loads using stirred, tubular or loop reactors. The polymers or copolymers of conjugated dienes - produced in step a) preferably have a mean molecular weight of between 500 and 1., 000,000. Preferred are copolymers of dienes such as 1,3-butadiene or isoprene, with vinylaromatic compounds such as styrene and α-methylstyrene. These polymers include the statistical co-polymers, where the comonomers are randomly distributed along the polymer chain, the graft copolymers and the block copolymers, pure or gradual. The block copolymers are especially interesting, since some of them are thermoplastic elastomers, industrially useful, such block sopolymers are composed of: a) at least one polymer block A obtained by -polymerization of an aromatic hydrocarbon containing a vinyl group, such as styrene or a-methylstyrene and b) at least one polymeric block B obtained by -polymerization of a conjugated diene such as 1,3-butadiene-no or isoprene. The block copolymers preferably used in the present invention are those containing from 10 to 90% by weight of vinylaromatic hydrocarbon. Particularly preferred are those copolymers whose content of 1,2-vinyl bonds in the conjugated diene are between 25 and 75% by weight. When the block copolymers of these characteristics are hydrogenated, the polydiene blocks are converted into blocks of polyolefins which behave as thermoplastic elastomers, of great industrial value. In step b) the deactivating compound R-OH or R-COOH preferably has a very good water-solubility and / or a boiling point higher than 110 ° C. When the compound R-OH or R-COOH satisfies this condition, it is easy to separate from the polymerization-hydrogenation solvent. Preferred alcohols as deactivating agents are ethylene glycol and 2-phenyl-2,4-pentanediol. When the deactivating compound is selected -between the compounds of formula R'n-Si-Cl4.-n, R'n-Sn-Cl4.-n, these remain bonded to the polymer chain, and, using compounds containing more of two chlorine atoms, it is possible to prepare polymers in the form of a star. In step c) it is possible to use any catalyst that can selectively hydrogenate olefinic double bonds without hydrogenating the aromatic ring, if present. The preferred catalysts are titano-ceno type compounds, such as those described for example in EP-A-601 953, EP-A-545 844, US-A-4, 673, 714 and US-A-4, 501 , 857, whose re-lation is included here as a reference. The most preferred catalysts are those of the formula Cp ^ Ti (PhQR) _ and Cp "Ti (CH-PPh)". These catalysts do not require the use of a cocatalyst and have a very high activity and selectivity in the hydrogenation of olefinic double bonds. In the process described in the present invention, the compound formed in the deactivation step by the reaction of the active lithium does not interfere with the activity of the hydrogenation catalyst. The amount that is formed of this -compound depends on the molecular weight of the polymer, whereby the hydrogenation process of the present invention is not affected by the molecular weight of the polymer to be hydrogenated. The use of finished polymers in this invention allows the polymers to be stored under an inert atmosphere since the hydrogenation step is not affected by the time elapsed since the polymerization step. This fact is advantageous from the industrial point of view, providing the process with greater flexibility. Hydrogenation products can be easily separated from the solvent used by known processes such as distillation, precipitation, etc. In particular - partially or totally hydrogenated polymers and copolymers can be separated from the solvent by the following procedures: 1) Contacting the hydrogenated solution with a polar solvent such as acetone, methanol or the like which, being a poor polymer solvent, cause its precipitation and allow its physical separation. 2) Contacting the hydrogenated solution with water and steam and removing the solvent by evaporation, separating the water and drying the polymer. 3) Evaporating directly the solvent. The process for the preparation of hydrogenated rubbers according to the invention is illustrated below by means of examples.

EXAMPLES The polymers to be hydrogenated were synthesized by anionic polymerization in solution of a mixture of cyclohexane and n-hexane, using as polymerization initiator n-butyl lithium and as polar modifier tetrahydrofura no. The monomers used were styrene and 1,3-butadiene no. From the synthesized polymers samples were removed for analysis, determining the proportion of styrene, butadiene, the ratio of vinyl addition of the polybutadiene and the average molecular weight. All the hydrogenations were carried out in stirred reactors, passing hydrogen through the polymer dissolution. Said solution is in all cases the result of the polymerization without any intermediate treatment. The hydrogenation catalysts used were Cp2Ti (PhOCH_) or Cp Ti (CH2PPh2) "and were added to the reactor in solution of a mixture of cyclohexane and tetrahydrofuran. The hydrogenation reactions were followed by the flow of hydrogen that the reaction demands, being-completed when this flow is zero. The percentage of final hydrogenation is analyzed by Proton Nuclear Magnetic Resonance (H-NMR). The percentages of hydrogenation refer to the butadiene fraction, since in no case is hydrogenation of the styrene aromatic ring observed. The hydrogenated polymers are recovered from the solution by coagulation in a mixture of steam and water, by evaporating and subsequently condensing the solvent from the reaction. Subsequently, the polymers are dried.

EXAMPLE 1 Hydrogenation of a low molecular weight polymer finalized with 2-methyl-2,4-pentanediol In a 2 1 reactor a styrene-butadiene-styrene (SBS) copolymer in a concentration of 10% by weight is prepared by sequential addition of monomers, ending the -polymerization with 2-methyl-2,4-pentanediol in a molar ratio alcohol / active Li = 0.5, so that all the lithium it gives off. The completion reaction is instantaneous, although one minute is allowed to elapse to ensure complete mixing. The resulting polymer has a styrene content of 27% by weight and 40.4% vinyl addition in the butadiene fraction. The number-average molecular weight is 48200. The same solution is brought to 90 ° C, starting temperature of the hydrogenation reaction, 0.25-mmol of catalyst is added per lOOg of polymer and the reactor is pressurized with 8 Kg / cm of hydrogen. The hydrogen consumption is completed after 45 minutes of reaction. The percentage of hydrogenation reached is 99.6%.

EXAMPLE 2 Hydrogenation of a high molecular weight polymer finalized with 2-methyl-2,4-pentanediol In a 20 1 reactor, a 10 wt% SBS copolymer is prepared in the same way as Example 1, but with the amount of initiator required for resulting in a high molecular weight polymer. Analysis of the polymer indicates a styrene content of 35.5% by weight, a vinyl addition of 42.4% and a number average molecular weight of 190800. The hydrogenation reaction starts at 100 ° C on the same solution. of polymer, the amount of -catalyst being 0.15 mmol per 100 g of polymer 2 and the hydrogen pressure of the reactor of 15 Kg / cm. The total reaction time was 62 minutes and the -reaction percentage reached 99.9%.

EXAMPLE 3 Hydrogenation of a polymer finished with ethylene glycol In a 20 1 reactor, a SBS copolymer is prepared in the same manner as in Example 1 except that the polymerization terminator used is ethylene glycol in a molar ratio ethylene glycol / active Li = 0.5, so that no Li remains active. in the polymer chains. The polymer concentration was 17% by weight. Analysis of the polymer resulted in 29.7 wt.% Styrene, 38.9 wt.% Vinyl addition and a number average molecular weight of 73280.

The hydrogenation reaction is carried out on the polymer solution at 15 kg / cm of hydrogen pressure, - the reaction starts at 85 ° C and the reaction is completed in 45 minutes with a catalyst consumption of 0.14 mmol per 100 polymer graph. The final hydrogenation percentage was 99.8%.

EXAMPLE 4 Hydrogenation of a polymer finished with a non-alcoholic compound (trimethyl chlorosilane) In a 20 1 reactor, an SBS copolymer is prepared in the same manner as in Example 1 except that the polymerization terminator used is trimethylchlorosilane in a finalizing molar ratio / active Li = 1, so that no active Li remains in the polymer chains. With this type of finishers do not form alkoxide type compounds. The polymer concentration was 10% by weight. Analysis of the polymer resulted in 27.2 wt.% Of styrene, a vinyl addition content of 44.1% and a number-average molecular weight of 58,000. The hydrogenation reaction of this 2-polymer solution was initiated at 90 ° C, and at a pressure of lOKg / cm, with the addition of 0.25 mmol / 100 g of rubber. A hydrogenation percentage of the butadiene fraction of 99.1% was reached in 75 minutes.

EXAMPLE 5 Hydrogenation of a radial polymer or star In a 2 1 reactor, styrene and butadiene are sequentially polymerized with n-butyl lithium as initiator and -tetrahydrofuran as a polar modifier, to synthesize a styrene-butadiene copolymer, which is reacted with -SiCl., As a coupling agent for 5 minutes, thus obtaining a styrene-butadiene-styrene copolymer with radial structure in four arms. The polymer thus synthesized had a styrene content of 27.9% by weight, 42.5% vinyl addition and a number average molecular weight of 93400. The coupling percentage was 96.5%. This polymer was then hydrogenated in the same solution at an initial temperature of 90 ° C, at 8 Kg / cm 2 of hydrogen pressure and with 0.25 mmol of catalyst-for every 100 g of polymer. The reaction took 40 minutes. The percentage of hydrogenation was 99.8%. The polymer did not undergo any expansion in the distribution of molecular weights, ie there was no uncoupling of chains.

Claims (7)

1. A process for the production of hydrogenated rubbers characterized by: A. polymerization in solution of one or more monomers in the presence of an alkyl lithium to produce polymers or copolymers of conjugated dienes; B. Addition to the reaction mixture of a compound is selected from the following classes: R-OH, R-COOH, -R'n-Si-Cl4.-n, 'R'n-Sn-Cl4.-n , wherein n comp is between 0 and 3, inclusive, in an amount of equivalents that is at least equal to the amount of polymerization catalyst, where R is a C2-C0 alkyl group optionally containing one or more polar functional groups selected from C-OH, COOH and such that the compound has a ratio of solubilities between water and hydrogenation solvent greater than 49 and / or a boiling point greater than 110 ° C; R * is a C-C alkyl group or a Cfi-C_0 aryl group; C. Hydrogenation of the deactivated polymer by addition to the mixture of a hydrogenation catalyst and maintaining the mixture under hydrogen pressure in a continuous, batch or batchwise manner using stirred, tubular or loop type reactors.

2. A process according to claim 1, characterized in that in step b) the deactivating compound is selected from ethylene glycol and 2-methyl-2,4-pentanediol.

3. A process according to claim 1 characterized in that in step a) copolymers of conjugated dienes such as 1,3-butadiene or isoprene are prepared with vinylaromatic compounds such as styrene or α-methylstyrene.

4. A process according to claim 3, characterized in that a block copolymer of butadiene-styrene is prepared in step a).

5. A process according to claims 1 to 4, characterized in that the average molecular weight of the polymer is between 500 and 1000000.

6. A process according to claims 1 to 5, characterized in that in step c ) The catalyst used is a titanocene compound, optionally in the presence of a cocatalyst.

7. A process according to claim 5, characterized in that the catalyst used is chosen from Cp2Ti (PhOR) 2 and Cp2Ti (CH2PPh2) 2.