GB2061961A - Catalytic hydrogenation of diene copolymers - Google Patents

Abstract

In the catalytic hydrogenation of a copolymer of a conjugated diene and a vinyl-substituted aromatic hydrocarbon, metallic rhodium supported on a carrier is used as a catalyst and said copolymer is hydrogenated in an inert solvent in the presence of said catalyst at a temperature of not more than 120 DEG C. The process is especially suitable for hydrogenating block copolymers, the diene portion being selectively hydrogenated.

Description

SPECIFICATION Method for the selective hydrogenation of polymers This invention relates to a method for the catalytic hydrogenation of a copolymer of a conjugated diene and a vinyl-substituted aromatic hydrocarbon to impart to the copolymer thermal stability, weather-resistance and ozone-resistance, and more particularly, this invention relates to such a catalytic hydrogenation method that the hydrogenation reaction can be conducted at a lowtemperature under a low hydrogen pressure, the sonjugated diene portion can be selectively hydrogenated, and the catalyst can be separated by a physical method after the reaction.

Copolymers of conjugated dienes and vinyl-substituted aromatic hydrocarbons are poor in thermal Stability, weather-resistance and ozone-resistance because they have carbon-carbon double bonds in the conjugated diene units. Said poor thermal stability, weather-resistance and ozone-resistance are a problem because the block copolymers of conjugated dienes and vinyl-substituted aromatic hydrocarbons are used without vulcanization as a thermoplastic elastomer, a transparent, high-impact resin or a modifier for polystyrene or olefin resins, and the uses of such block copolymers are limited.

These defects are generally considered to be attributable to the unsaturated bonds, and these properties of said copolymers are greatly improved by hydrogenating the carbon-carbon double bonds in the diene portion of the copolymer.

There are known the following two types of catalysts which are usable for said hydrogenation reaction: (1) so-called Ziegler type homogeneous-system catalysts obtained by reacting an organic acid salt of nickel or cobalt or an acetylacetone salt of nickel or cobalt with a reducing agent such as an organic aluminum in a solvent, and (2) carrier-supported catalysts in which a metal such as nickel, palladium, ruthenium, or the like is supported on a carrier such as carbon, alumina, silica, silica-alumina, diatomaceous earth, or the like.

The Ziegler type homogeneous-system catalysts, as compared with the carrier-supported catalysts, have the advantages that they enable the reaction to proceed at a lower temperature under a lower hydrogen pressure and that they enable the conjugated diene portion in the copolymer of a conjugated diene and a vinyl-substituted aromatic hydrocarbon to be selectively hydrogenated.

However, the polymer solution after the hydrogenation is apparently homogeneous and it is impossible to separate the catalyst by a physical method such as filtration. Therefore, as disclosed in Japanese Patent Application Kokai (Laid-Open) No.37482/73, it is necessary to effect such complicated chemical reactions that the catalyst is first oxidized with an oxidizing agent such as hydrogen peroxide, the oxidized catalyst is reacted with tartaric acid, and the reaction product is then extracted with an alcohol. The said catalyst removal is always required because any catalyst residue in the polymer adversely affects the weather- and heat-resistance of the polymer.

On the other hand, the carrier-supported catalysts are generally low in activity and necessitate high-temperature and high-pressure conditions for the hydrogenation reaction. Particularly since the reaction proceeds when the polymer is contacted with carrier-supported catalyst, high polymers are more liable to suffer a serious steric hindrance than liquid polymers having a low polymerization degree, and hence, the high polymers are difficult to hydrogenate. Therefore, the high-temperature and high-pressure conditions are particularly required for hydrogenating polymers having a high polymerization degree, and in this case decomposition or gelation of the polymer tends to be caused.

Also, the carrier-supported catalysts generally lack hydrogenation selectivity, and hence, the conjugated diene portion and the aromatic nucleus portion are simultaneously hydrogenated. For example, GB 2,011,911 discloses a method for hydrogenating a styrene-butadiene-styrene type three-block copolymer with a platinum catalyst supported on alumina, and according to the Examples thereof, when hydrogenation is conducted at a temperature of 150"C under a hydrogen pressure of 10 kg/cm2, the hydrogenation conversions of both the butadiene and styrene portions are substantially the same and no selectivity is observed.Hydrogenation of the conjugated diene portion only is sufficent for improvement in heatresistance, weather-resistance and ozone-resistance, and hydrogenation of the aromatic nucleus portion gives no merit in respect of physical properties and rather results in a disadvantage of increased hydrogen consumption.

'It is said that the carrier-supported catalyst is easy to separate by a physical method after hydrogenation, but this applies only to the organic compounds or polymers of a low polymerization degree. In the case of polymers of a high molecular weight, the separation of the catalyst is not always easy because the solution viscosity is extremely high, or the polymer becomes insoluble in the solvent to turn the solution into a pudding-like state.

According to this invention, there is provided a method for the catalytic hydrogenation of a copolymer of a conjugated diene and a vinyl-substituted aromatic hydrocarbon, wherein the hydrogenation is effected using a catalyst of metallic rhodium supported on a carrier in an inert solvent at a temperature of not more than 120"C.

Using the method of this invention, it is possible to selectively hydrogenate at least 70% of the conjugated diene portion and not more than 30% of the vinyl-substituted aromatic hydrocarbon portion.

It has also been found that when using a copolymer in which the combined weight of the vinyl-substituted aromatic hydrocarbon polymer block content (a) and the vinyl content (b) of the conjugated diene, namely (a + b), is 30% by weight or more of the whole of the copolymer, it is possible to separate the catalyst from the solution buy a physical method afterthe reaction, and the catalyst separated and recovered by the physical method can be used repeatedly as a catalyst for further hydrogenations, with its activity remaining substantially unchanged.

The conjugated diene in the conjugated diene-vinyl-substituted aromatic hydrocarbon copolymer used in this invention may be, for example, butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, while the vinyl-substituted aromatic hydrocarbon in said polymer may be, for example, styrene, t-butyl-styrene, methylstyrene, divinylbenzene, 1,1-diphenylethylene. However, butadiene and isoprene are preferred for use as the conjugated diene in this invention while styrene is preferred for use as the vinyl-substituted aromatic hydrocarbon.

The vinyl-substituted aromatic hydrocarbon content in said copolymer is preferably within the range of 5 to 95% by weight; the characteristic features of the copolymer are not fully retained if said hydrocarbon content is outside the said range.

The copolymer used in this invention includes random copolymers, tapered block copolymers and perfect block copolymers, though it is desirable that the sum of the vinyl-substituted aromatic hydrocarbon polymer block content (a) in the copolymer and the vinyl content (b) in the conjugated diene portion, namely a + b, is not less than 30% by weight of the whole of the copolymer. If said sum (a + b) is less than 30% by weight, the reaction product solution becomes too viscous or the polymer becomes insoluble whereby the whole solution becomes a pudding-like state and hence separation of the catalyst becomes difficult. Also, there often occurs crosslinking or gelation of the hydrogenated polymer.

The vinyl-substituted aromatic hydrocarbon polymer block content (a) was measured according to the method disclosed in L.M. Kolthoff et al, j. Polymer Sci., 1,429 (1946), and it was expressed in terms of the block polymer content in the whole polymer.

The vinyl content (b) in the conjugated diene portion of the polymer was determined by first calculating the vinyl content in the conjugated diene portion according to Hampton's method (R.R. Hampton, Anal.

Chem. 29,923 (1949)) by using an infrared absorption spectrum and converting the calculated value to a weight ratio to the whole polymer. The wave-numbers used, in the case of SBR, were 724 cm1 for cis-1,4 of butadiene, 967 cm7 for trans-1,4, 911 cml for 1,2-vinyl and 699 cm1 for styrene, from which the concentrations of the respective components can be determined.

The copolymer used in this invention is preferably a block copolymer having a vinyl-substituted aromatic hydrocarbon polymer block content of not less than 10% and not more than 90%, more preferably not less than 20% and not more than 50% when the copolymer is designed to be used as a thermoplastic elastomer and not less than 60% and not more than 90% when the copolymer is designed to be used as a thermoplastic resin.The term "block copolymers" used herein refers to copolymers having at least one polymer block A consisting mainly of a vinyl-substituted aromatic hydrocarbon and at least one polymer block B consisting mainly of a conjugated diene and the copolymer may be represented by the following general formulae, in which a small quantity of conjugated diene may be contained in the block A and a small quantity of vinyl-substituted aromatic hydrocarbon may be contained in the block B: AfB - A)rn, B -A+B A)n, { (A - B)p+qX, and {B+A - B)p+qX wherein m = 1-Sn n = 0-5, p = 1-5, q = 2-10, and X represents carbon, silicon, tin, divinylbenzene or the like.

The straight-chain polymers represented by the general formulae A+B - A)m and BA+B - A)n can be produced by successively adding and polymerizing a conjugated diene monomer and a vinyl-substituted aromatic hydrocarbon monomer by using an organic alkali metal catalyst.

The branched, radial or star-shaped block copolymers represented by the formulae, { (A - B)p }qX and { B+ A - B)p+qX, can be produced by coupling the living terminals of the block copolymers formed in the manner mentioned above with a coupling agent such as halogenated hydrocarbon, silicon tetrachloride, tin tetrachloride, divinylbenzene, or the like.

More preferably, the block copolymers used in this invention are of the type that the micro-structure of the conjugated diene portion comprises 30 to 70% of 1,2-configuration and 30 to 70% of 1,4-configuration (cis-configuration and trans-configuration). Since the olefin portion of the block copolymer of this type has a rubbery elasticity after hydrogenation, the block copolymer is not only high in industrial value but also advantageous for separation of the catalyst because of extremely low viscosity of the hydrogenated polymer solution.

The weight-average molecular weight of the copolymer used in this invention, as measured by GPC, is preferably between 20,000 and 1,000,000. If said molecular weight is less than 20,000, the hydrogenated polymerthus obtained is poor in mechanical properties, and if said molecular weight is more than 1,000,000, the polymer produced is poor in processability.

As the carrier on which metallic rhodium is supported in this invention, there may be employed known carriers such as carbon, alumina, silica-alumina, diatomaceous earth, etc., among which carbon and alumina are preferred. Particularly, when metallic rhodium is supported on carbon, the catalyst can be easily separated from the hydrogenated polymer solution. The particle size of the carrier may be selected from the commonly used range of particle size, for example, 0.1 to 500 u The most preferred range, however, is from 10 to 200 .

In the inert solvents used in this invention include aliphatic and alicyclic saturated hydrocarbons such as cyclohexane, hexane, heptane, octane, etc., tetrahydrofuran, chlorinated hydrocarbons and mixtures thereof. Since the copolymer used for the hydrogenation according to this invention is usually produced in an inert hydrocarbon solvent, it is advantageous to use the solution immediately (in the form as it is) for hydrogenation.

Various kinds of alcohols and ethers have a function to activate the catalyst, so that they may be added to the solvent in such an amount as will not affect the solubility of the polymer.

The hydrogenation temperature used in this invention is not more than 1200C, preferably not more than 100 C. If the hydrogenation temperature exceeds 1 200C, the desired hydrogenation selectivity for the conjugated diene portion and aromatic nucleus portion is not obtained. When a high hydrogenation selectivity is required, the hydrogenation temperature is preferably not more than 45 C. The lower the hydrogenation temperature, the better the selectivity becomes but the lower the hydrogenation rate.

The hydrogen pressure used in this invention is from normal pressure to 200 kg/cm2.

The hydrogenation reaction time is from one minute to 20 hours.

The hydrogenation reaction may be of any known system such as, for example, fixed bed system or suspension system. In the case if suspension system, for instance, the hydrogenation is performed by adding a polymer solution and a catalyst and stirring the mixture at a predetermined temperature under a predetermined hydrogen pressure. The reaction may be of either batch-wise system or continuous system.

Tracing the progress of the reaction by checking the amount of hydrogen absorbed, it is possible to obtain a hydrogenated copolymer of this invention in which the hydrogenation conversion of the diene portion is not less than 70% and that of the aromatic nucleus portion is not more than 30%. If the hydrogenation conversion of the diene portion is less than 70%, no satisfactory improvement of heat-resistance, ozone-resistance and weather-resistance is obtained. Also, if the hydrogenation conversion of the aromatic nucleus portion exceeds 30%, no improvement of properties of the product is obtained, and rather the excellent moldability of the vinyl-substituted aromatic hydrocarbon polymer block is lost. Further, a large volume of hydrogen is consumed and a long time is required for the hydrogenation of the aromatic nucleus, resulting in an elevated production cost.

The hydrogenation conversion was determined from the ultraviolet absorption spectrum and infrared absorption spectrum. To put it more definitely, the hydrogenation conversion of the styrene portion was calculated from the following equation by measuring the styrene content in the polymer from the absorption due to the styrene portion at 250 m in the ultraviolet absorption spectrum.

Styrene content in polymer after hydrogenation conversion (%) of = (1 - ) x 100 Styrene content in polymer styrene portion before hydrogenation The hydrogenation conversion of the butadiene portion was calculated from the ratio # of the content of the diene remaining unhydrogenated to the content of the styrene remaining unhydrogenated in the polymer as determined from the infrared absorption spectrum of the hydrogenated polymer and the styrene contents in the polymers before and after hydrogenation as determined above.

Butadiene content (unhydrogenated diene content) in polymer after hydrogenation Styrene content (unhydrogenated styrene content) in polymer after hydrogenation Butadiene content in polymer after hydrogenation conversion (%) = (1 - . ) x 100 of butadiene Butadiene content In polymer portion v(Styrene content in polymer = (1 after hydrogenation) x 100 Styrene content in (1 - polymer before ) hydrogenation The catalyst can be separated and recovered by a physical method such as decantation, filtration, filtration under pressure, centrifugation, centrifugal precipitation, or the like from a polymer solution obtained by hydrogenating a copolymer in which (a + b) is not less than 30% by weight of the whole copolymer according to the method of this invention.Generally, the lower the hydrogenation temperature and the shorter the reaction time, the easier the separation and recovery of the catalyst becomes. When the catalyst separation is accomplished favorably, the catalyst settles out naturally and the filtrate becomes almost transparent.

The recovered catalyst can be reused as it is or after being washed with a solvent. Since metallic rhodium is expensive, the recovery and reuse of the catalyst is the essential requirements, and the fulfillment of such requirements has a great significance in industry.

As described above, this invention has made it possible to selectively hydrogenate the conjugated diene portion in a copolymer of a conjugated diene and a vinyl-substituted aromatic hydrocarbon even with a carrier-supported catalyst. The invention has also made it possible to recover and reuse the catalyst.

The hydrogenated copolymers obtained according to the method of th is invention are used as thermoplastic elastomers or thermoplastic resins or as rubbers with excellent weather resistance and heat resistance. Also, these hydrogenated copolymers may be mixed with a stabilizer, a ultraviolet absorber, an oil, a filler and other additives for practical use.

This invention is explained in further detail before referring to Examples. These Examples are merely by way of illustration and not by way of limitation. In the Examples and Referential Examples, parts and percentages are by weight unless otherwise specified.

Referential Example 1 Into an autoclave were charged 400 g of cyclohexane, 15 g of styrene monomer and 0.11 g of n-butyl lithium, and these were subjected to polymerization at 60"C for 3 hours, after which 70 g of monomeric butadiene was added and the mixture was subjected to polymerization at 60 C for 3 hours. Finally, 15 g of monomeric styrene was added and the mixture was subjected to polymerization at 60"C for 3 hours to obtain a styrene-butadiene-styrene type three-block copolymer having a weight-average molecular weight of about 60,000 and also having a combined styrene content of 30%, a blocked styrene content of 29.5% and a 1,2-configuration content in the butadiene portion of 13% to based on the whole polymer).

Referential Example 2 To 500 g of cyclohexane were added 30 g of monomeric styrene and 0.45 g of n-butyl lithium, and polymerized at 60"C for 3 hours, after which 70 g of monomeric butadiene and tetrahydrofuran (THF) were added a molar ratio of n-butyl lithium/tetrahydrofuran = 20 and the mixture was subjected to polymerization at 40"C for 2 hours. Silicon tetrachloride was thereafter added in an amount of 1/4 mole of the catalyst amount to effect coupling. The properties of the polymer obtained are shown in Table 1.

Referential Example 3 Cyclohexane (1,200 g/hr), monomeric butadiene (210 g/hr), n-butyl lithium (1,350 g/hr) and tetrahydrofuran (n-BuLi/THF molar ratio = 30) were continuously supplied to a 1 litre-vessel type reactor with a height/diameter ratio of 4 at the bottom while monomeric styrene was supplied from the top at a rate of 90 g/hr, and the resulting mixture was subjected to polymerization at a temperature of 100"C with an average residence time of 25 minutes and the formed polymer solution was continuously withdrawn from the reactor. The properties of the polymer obtained are shown in Table 1.

Reherential Example 4 To 400 g of cyclohexane were added 70 g of monomeric butadiene, 20 g of monomeric styrene, 0.9 g of tetrahydrofuran and 0.05 g of n-butyl lithium, and the mixture was subjected to polymerization at400C for 2 hours, after which 10 g of monomeric styrene was added and the mixture was subjected to polymerization at 60 C for one hour. The properties of the polymer obtained are shown in Table 1.

Referential Example 5 Into an autoclave were charged 400 g of cyclohexane, 70 g of monomeric butadiene, 30 g of monomeric styrene, 0.05 g of n-butyl lithium and 0.9 g of THF simultaneously, and the mixture was subjected to polymerization at 400C for 2 hours. The properties of the polymer obtained are shown in Table 1.

Referential Example 6 In a 2-liter autoclave were charged 400 g of cyclohexane and 0.05 g of n-butyl lithium, and a butadiene/sWrene (70/3G) monomer mixture solution was then supplied thereto at a constant rate for a period of 3 hours by using a metering pump to effect polymerization while maintaining the autoclave at 900C.

The total amount of the monomers supplied was 100 g. After the completion of the supply of the monomers, the polymer solution was withdrawn from the autoclave. The properties of the polymer obtained are shown in Table 1.

Referential Example 7 A block copolymer with a high styrene content was synthesized in the same way as in Referential Example 1, except that the amounts of the monomeric styrene supplied at the first and third stages were 40 g (total: 80 g) and the amount of the monomeric butadiene supplied was 20 g. The properties of the polymer obtained are shown in Table 1.

Referential Example 8 A styrene-isoprene-styrene type block copolymer was synthesized in the same way as in Referential Example 1, except that isoprene was substituted for the butadiene. The properties of the polymer obtained are shown in Table 1.

TABLE ! Properties of the polymers before hydrogenation Sample No. 1 2 3 4 5 Referential Example No. (1) (2) (3) (4) (5) Bonded styrene (%) 30 30 30 30 30 Blocked styrene (a) (%) 29.5 30 10.5 10.2 0 Micro- 1,2-configustructure ration 15 50 40 15 50 of diene portion cis-configu (%) ration 85 50 60 85 50 1,2-Configuration content (b) (%) 10.5 35 28 10.5 35 (a) + (b) (%) 40 65 38.5 20.7 35 Molecular weight1) 60,000 60,000 180,000 190,000 200,000 Structure A-BA (A-B)qSi A-B type A-B type Randum A: styrene block type block type block block SBR B: diene block polymer -Cont'd Note 1): "Molecular weight" is the weight-average molecular weight measured by GPC.

2): Trade name of Nihon Soda K.K. for a polybutadiene.

3): Trade name of Asahi Kasei Kogyo K. K. for a diene polymer.

TABLE 1 (Cont'd) 6 7 8 9 10 (6) (7) (8) NISSO-PB B-3000 2) Diene-35 3) 30 80 30 0 0 0 78 29.5 0 0 15 15 10 90 15 85 85 90 10 85 10.5 3 7 90 15 10.5 81 37.5 90 15 190,000 60,000 60,000 3,000 ca. 200,000 A-B-A A-B-A type Randum type block Polybutadiene Polybutadiene SBR block polymer polymer (B: isoprene) Examples 1 to 6 The polymer solutions (Sample Nos. 1-8) synthesized in Referential Examples 1-8 respectively were diluted with the same quantity of cyclohexane to reduce the polymer concentration to 10% and then subjected to hydrogenation reaction (the products being designated as Sample Nos. 1-8, respectively).

Separately from this, liquid polybutadiene NISSO-PB, B-3000 and Diene-35were dissolved in cyclohexaneto a concentration of 10% and then subjected to hydrogenation reaction (Sample Nos. 9 and 10).

Used as catalyst was rhodium carbon Rh/C (the amount of rhodium supported: 5%; the carrier carbon was active carbon powder with an average particle size of 20-40 microns and a specific surface area of approximately 1,100 m2/g) produced by Nippon Engerhard, Ltd., and 1,000 g of each polymer solution (polymer: 100 g) and 20 g of the catalyst Rh/C (1 g as calculated in terms of metallic rhodium) were added to a 2-litre autoclave equipped with a stirrer, and after replacing the air in the autoclave with hydrogen, the mixture was subjected to hydrogenation reaction under vigorous stirring at a constant temperature (80"C) under a constant hydrogen pressure (50 kg/cm2 G) for 90 minutes. Thereafter, the reaction product solution was returned to room temperature and normal pressure and then taken out of the autoclave.The state of the solution was observed and the catalyst was separated by filtration through a pressure filter. Filter cloth #400 pre-treated with plain carbon was used for the pressure filter. A large quantity of methanol was added to each catalyst-removed polymer solution to precipitate the polymer.

The hydrogenation conversion of each polymer obtained, the state of the reaction product solution, filtering characteristics (easiness to filter) and the state of each hydrogenated polymer are shown collectively in Table 2.

TABLE 2 Results of the hydrogenation reaction Example 1 Example 2 Example3 Sample No. 1 2 3 Hydrogenation conversion of diene portion (%) 89 97 95 Hydrogenation conversion of styrene portion (%) 12 10 7 Low-viscosity State of reaction homogeneous Same as left Same as left product solution solution Fiitering chracter istics Filterable Filterable Filterable State of hydrogenated Flexible polymer at room Hard and thermoplastic Same as left temperature resinous elastomer TABLE 2 (Cont'd) Example 4 Example 5 Example 6 Example 7 Example 8 4 5 6 7 8 85 93 82 88 80 10 9 10 5 8 Low-viscosity Pudding- or Low-viscosity Pudding-or homogeneous slurry-like homogeneous Same as left slurry-like solution solution Heating and Heating and dilution with dilution with solvent were Filterable solvent were Filterable Filterable required required Flexible Hard and Flexible Hard and Soft thermoplastic resinous thermoplastic resinous rubber-like elastomer elastomer TABLE 2 (Cont'd) Comparative Comparative Example 1 Example 2 9 10 93 89 Same as left Pudding-like Heating and dilution with Filtrable solvent were required Liquid Soft resin-like As shown in Table 2, each of the hydrogenation product solutions obtained in Examples 1-3,5,7 and 8 and Comparative Example 1 is a low-viscosity homogeneous solution and can be separated by filtration under pressure. Particularly, in the case of Examples 2,3 and 5 with a high 1, 2-configuration content, the hydrogenation rate is high and also the hydrogenated polymer solution is low in viscosity and easy to separate.

In Examples 4 and 6, the hydrogenation product was pudding-like, and for removing the catalyst therefrom, it was necessary to dilute the solution to a polymer concentration of not more than 1 % and then filter it under heating at 60 - 700C. The liquid polybutadiene of Comparative Example 1 was filterable but the high-molecular-weight polybutadiene of Comparative Example 2 was pudding- or slurry-like and insoluble in the solvents and hence was difficult to separate.

It will be also noted that the hydrogenation conversion of the diene portion of each polymer is very high, indicating that most of the hydrogen has been consumed for the hydrogenation of the diene portion.

Examples 9 to 11 The styrene-butadiene-styrene three-block copolymer solution of Sample 2 prepared in Referential Example 2 was diluted with the same quantity of cyclohexane to a polymer concentration of 10% and then hydrogenated under the conditions shown in Table 3. The results are also shown in Table 3.

TABLE 3 Comp. Comp. Comp. Comp. Comp.

Example 9 Example 10 Example 11 Ex. 3 Ex.4 Ex.5 Ex.6 Ex.7 Rh/C Ru/Al2O3 Ru/Al2O3 Pd/C Catalyst (produced Same as Same as Same as (produced (produced (produced Same as by Nippon left left left by Nippon by Nippon by Nippon left Engerhard) Engerhard) Engerhard) Engerhard) Catalyst/ polymer (%) 20 20 20 20 20 20 20 20 Polymer concentration (%) 5 5 5 5 5 5 5 5 Hydrogen pressure (kg/cm) 50 50 50 50 70 100 50 50 Hydrogenation temperature ( C) 80 70 100 130 100 140 80 140 Hydrogenation time (min.) 60 90 30 10 120 13 hr. 60 60 Hydrogenation conversion of butadiene 96 99 90 71 Nearly 0 60 10 50 portion (%) Hydrogenation conversion of styrene 11 10 25 40 Nearly 0 51 13 55 portion (%) As seen from Table 3, in case of using Rh/C as catalyst, excellent selectivity is obtained at hydrogenation temperatures of 70"C, 80"C and- 100 C, and generally, the lower the temperature, the better the selectivity is.

At 130q the hydrogenation conversion of the styrene portion increases to 40% while that of the diene portion is only slightly above 70%. When it is attempted to elevate the hydrogenation conversion of the diene portion at 1300C, the hydrogenation conversion of the styrene portion exceeds 60%.

On the other hand, in case of using an alumina-supported ruthenium catalyst (Ru/AI203), the hydrogenation does not advance substantially-at low temperatures, and when the temperature is elevated to 140 C, although the hydrogenation advances, its rate is very low and further no selectivity is seen.

In case of using acarbon-supported palladium catalyst (Pd/C), the hydrogenation rate was higher than that in the case of the ruthenium catalyst, but no selectivity was seen in this case, too.

Example 12 The catalyst used in Example 2 was separated and recovered, and the hydrogenation was carried out with this recovered catalyst under the same conditions as in Example 2. The hydrogenation performance, as shown below, was almost the same as in Example 2.

Hydrogenation time: 90 min.

Hydrogenation conversion ofthe butadiene portion: 95% Hydrogenation conversion of the styrene portion: 11% Example 13 Hydrogenation was carried out under the same conditions as in Example 2, except that an aluminasupported rhodium catalyst was used. The results were almost the same as in Example 2 as shown below.

Hydrogenation time: 100 min.

Hydrogenation conversion of the butadiene portion: 92% Hydrogenation conversion of the styrene portion: 13% The catalyst was precipitated by using a centrifugal separator at 15,000 r.p.m. and separated by decantation.

Example 14 Hydrogenation was carried out under the same conditions as in Example 2, except that the reaction temperature was 40"C, and the reaction time was 5 hours. The results obtained were as follows: Hydrogenation conversion of the butadiene portion: 84% Hydrogenation conversion of the styrene portion: Nearly0%

Claims (13)

1. A method for the catalytic hydrogenation of a copolymer of a conjugated diene and a vinyl-substituted aromatic hydrocarbon, wherein said hydrogenation is effected in an inert solvent at a temperature of not more than 1200C using metallic rhodium supported on a carrier as a catalyst.

2. A method according to Claim 1, wherein the copolymer is a block copolymer in which the combined weight (a + b) of (a) the vinyl-substituted aromatic hydrocarbon polymer block portion and (b) the 1,2-configuration content of the conjugated diene portion is 30% by weight or more of the whole polymer.

3. A method according to Claim 2, wherein the catalyst is separated and recovered from the polymer solution by a physical method after the hydrogenation reaction and the recovered catalyst is reused for a further hydrogenation reaction.

4. A method according to Claim 1, 2 or 3, wherein the copolymer is selectively hydrogenated so that the hydrogenation conversion of the conjugated diene portion in the copolymer is not less than 70% by weight and that of the aromatic nucleus portion is not more than 30% by weight.

5. A method according to any one of Claims 1 to 4, wherein the weight-average-molecular weight of said copolymer is from 20,000 to 1,000,000.

6. A method according to any one of Claims 1 to 5, wherein said copolymer is a block copolymer containing the vinyl-substituted aromatic hydrocarbon polymer blocks in a proportion of not less than 10% by weight and not more than 90% by weight.

7. A method according to Claim 6, wherein said copolymer is a block copolymer containing the vinyl-substituted aromatic hydrocarbon polymer blocks in a proportion of not less than 20% by weight and not more than 50% by weight.

8. A method according to Claim 6, wherein said copolymer is a block copolymer containing the vinyl-substituted aromatic hydrocarbon polymer blocks in a proportion of not less than 60% by weight and not more than 90% by weight.

9. A method according to any one of Claims 1 to 8, wherein the microstructure of the conjugated diene portion in said copolymer comprises 30-70% by weight of units having 1,2-configuration and 30-70% by weight of units having 1,4-configuration.

10 0. A method according to any one of Claims I to 9, wherein the carrier is carbon. alumina, silica-alumina or diatomaceous earth.

11 A A method according to any one of Claims 1 to 10, wherein the hydrogenation temperature is not more than 45"C.

12. A method according to Claim 1, substantially as described in any one of the Examples

13. A hydrogenated copolymer obtained by a method according to any one of Claims I to 12