GB2117778A - Method for modifying unsaturated polymer rubber - Google Patents

Abstract

An alkali metal-containing unsaturated polymer rubber is modified by reaction with an aromatic ketone compound of the general formula <IMAGE> wherein R1 and R2 independently represent hydrogen, alkyl, cycloalkyl, alkenyl, alkoxy, amino, alkylamino, dialkylamino, or halogen, and m and n independently represent an integer of from 1 to 5. The modified rubber is useful in automobile tire tread.

Description

SPECIFICATION Method for modifying unsaturated polymer rubber This invention relates to a method for modifying an unsaturated polymer rubber. More specifically, it relates to a method for modifying an unsaturated polymer rubber containing an alkali metal by reacting it with a specified aromatic ketone compound.

In recent years, rubber materials having low rolling resistance and high wet skid resistance have been strongly desired for use in automobile tire treads because of the need for the low fuel costs and running safety of automobiles. These two properties, however, are intrinsicaily inconsistent with each other, and various methods of modifying polymers have been proposed in order to maintain them in harmony with each other.For example, with regard to a styrene-butadiene copolymer, a method in which the ratio between the content of vinyl units and the content of styrene units is adjusted to a specified range (Japanese Laid-Open Patent Publication No. 62248/1979), a method in which the styrene sequences are provided in a specified distribution (Japanese Laid-Open Patent Publication No. 143209/1981), and a method in which the vinyl sequences are provided in a specified distribution (Japanese Laid-Open Patent Publication No.

149413/1981) have been proposed. The improving effects of these methods, however, are only slight, and a further improvement is desired.

It was proposed, on the other hand, to improvefihe rebound of an active polymer having an alkali metal or an alkaline earth metal at its ends by reacting it with a specified aromatic thioketone compound, thereby introducing the SH group into the ends of the polymer (U. S. Patent No.3,755,269). It is known that rebound and rolling resistance are in inverse correlation with each other, and the higher the rebound, the lower the rolling resistance. Accordingly, the method disclosed in the U.S. Patent may also be said to be intended to reduce rolling resistance without impairing wet skid resistance.Since, however, the SH group in the polymer is very unstable to oxygen or heat and is readily decomposed by the action of oxygen or heat, contact of the polymer with air or its exposure to high temperatures of more than 150"C should be avoided. However, in the separation of a rubber polymer from a rubber polymer solution on an industrial scale, the polymer is sometimes exposed for a long time to high temperatures of more than 100"C in the coagulation and drying steps, and with some types of the rubber polymer or some methods of drying, heating is done to a temperature of 1 500C. Accordingly, the aforesaid method comprising the introduction of the SH group into the ends of the polymer cannot be free from the decomposition of the SH group in the coagulating and drying steps and the consequent occurrence of an irritating odor, and moreover, the effect of increasing the rebound of the polymer is lower than the intended level. For this reason, the method of the above-cited U.S.

Patent is difficult to practice industrially.

It is not known why a polymer having the SH group introduced into the ends of the polymer chain exhibits high rebound. Presumably, however, it has to do with the high activity of the SH group.

It is an object of this invention to provide a method which can improve the rebound of an alkali metal-containing unsaturated polymer rubber without impairing its wet skid resistance without resorting to the means of introducing the SH group in view of the various defects of the aforesaid known method comprising the introduction of the SH group into the ends of a polymer.

We have surprisingly found that a polymer obtained by reacting an alkali metal-containing unsaturated polymer rubber with a certain kind of aromatic ketone compound has increased rebound equivalent to the case of introducing the SH group into the ends of the polymer chain in spite of its having an atomic grouping (presumably the OH group) with lower activity than the SH group and irrespective of the position of this introduced atomic grouping in the polymer chain.

Thus, according to this invention, there is provided a method of modifying an unsaturated polymer rubber, which comprises reacting an alkali metal-containing unsaturated polymer rubber in solution with an aromatic ketone compound represented by the formula

wherein each of R1 and R2 represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy group, an amino group, an alkylamino group, a dialkylamino group, or a halogen atom, and each of m and n represents an integer of from 1 to 5.

By carrying out the method of this invention, an unsaturated polymer rubber having low rolling resistance and increased rebound without impairing wet skid resistance can be produced stably without taking any special measure for preventing decomposition of the introduced atomic grouping in the separating and drying steps.

The alkali metal-containing polymer used in this invention includes polymer rubbers having an alkali metal bonded to the chain ends of diene-type polymers obtained by polymerizing or copolymerizing conjugated diene monomers using an alkali metal-based catalyst, and rubbers resulting from the addition of alkali metals to unsaturated polymer rubbers having a double bond by any method of polymerization (solution polymerization, emulsion polymerization, etc.).

Examples of diene-type polymer rubbers include polymers or copolymers of conjugated diene monomers such as 1,3-butadiene, isoprene, 1 ,3-pentadiene, 2,3-dimethyl-1 ,3-butadiene and 1 3-hexadiene; and copolymers of conjugated diene monomers and monomers copolymerizable therewith (for example, aromatic vinyl compounds such as styrene, a-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene and divinylnaphthalene, unsaturated nitriles such as acrylonitrile, acrylic acid esters, methacrylic acid esters, and vinylpyridine). These examples are only illustrative. Specific examples of the diene-type polymer are polybutadiene rubber, polyisoprene rubber, butadiene/isoprene copolymer rubber, and butadiene/styrene copolymer rubber.

A diene-type polymer rubber in which an alkali metal is bonded to its chain ends is the aforesaid diene-type polymer rubber obtained by polymerization with an alkali metal-based catalyst. In this polymer, the alkali metal is bonded to at least one end of the polymer chain. The polymerization may be carried out without any restriction, and the alkali metal-based catalyst, polymerization solvent, randomizer, microstructure adjusting agent for the conjugated diene units, etc. used in this polymerisation may be those which are commonly used. The amount of the alkali metal-based catalyst is usually in the range of 0.1 to 10 millimoles per 100 parts by weight of monomer.

The polymer rubber resulting from the addition of an alkali metal to an unsaturated polymer means a polymer rubber obtained by polymerizing the aforesaid conjugated diene monomer or copolymerizing it with a copolymerizable monomer by an ordinary polymerization method such as a solution polymerization technique using an alkali metal-based catalyst or a Ziegler catalyst, or an emulsion polymerization technique using a redox catalyst to form a diene-type rubber, a polymer rubber obtained by polymerizing olefins or cyclo-olefins (specifically, polybutadiene rubber, polyisoprene rubber, butiadene/styrene copolymer rubber, butadiene/isoprene copolymer rubber, polypentadiene rubber, butadiene/piperylene copolymer rubber, butadiene-propylene alternate copolymer rubber, polypentenamer, polyoctenamer, ethylene/propylene/ diene terpolymer rubber, etc.), followed by addition of an alkali metal.

Addition of an alkali metal to the unsaturated polymer rubber can be carried out by methods commonly practiced. For example, this can be achieved by reacting the unsaturated polymer rubber in a hydrocarbon solvent at a temperature of 30 to 1 OO"C for a period of several tens of minutes to several tens of hours in the presence of an ordinary alkali metal-based catalyst and a polar compound such as an ether compound, an amine compound or a phosphine compound. The amount of the alkali metal catalyst is usually in the range of 0.1 to 10 millimoles per 100 g of the unsaturated polymer rubber. If it is less than 0.1 millimole, an increase in rebound cannot be obtained. If it exceeds 10 millimoles, side-reactions such as the crosslinking or cleavage of the polymer occur to reduce the increase of rebound.

The amount of the polar compound is usually 0.1 to 10 moles, preferably 0.5 to 2 moles, per mole of the alkali metal-based catalyst.

The alkali metal-based catalyst used in the polymerization and the addition-reaction is lithium, sodium, potassium, rubidium or cesium, or a complex of such a metal with a hydrocarbon compound or a polar compound. Preferably, it is a lithium compound having 2 to 20 carbon atoms. Specific examples include ethyllithium, n-propyllithium, i-propyllithium, n-butyllithium, sec-butyllithium, t-octyllithium, n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butylphenyllithium, 4-phenylbutyllithium, cyclohexyllithium, 4 cyclopentyllithium, 1 ,4-dilithio-butene-2, sodium naphthalene, sodium biphenyl, potassium4etrahydrofuran complex, potassium-diethoxyethane complex, and sodium salt of a-methylstyrene tetramer.

The polymerization reaction and the alkali metal addition reaction are carried out in a solvent which does not destroy the alkali metal-base catalyst, such as a hydrocarbon solvent, tetrahydrofuran, tetrahydropyran, or dioxane. Suitable hydrocarbon solvents are selected from aliphatic hydrocarbons, aromatic hydrocarbons, and alicyclic hydrocarbons. Especially preferred are hydrocarbons having 2 to 12 carbon atoms, such as propane, n-butane, t-butane, n-pentane, i-pentane, n-hexane, cyclohexane, propene, 1-butene, i-butene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene and ethylbenzene. These solvents may be used as a mixture of two or more.

The aromatic ketone compound used in this invention is a compound represented by the general formula

wherein each of R1 and R2 represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkeneyl group, an alkoxy group, an amino group, an alkylamino group, a dialkyiamino group, or a halogen atom. Specific examples of preferred aromatic ketone compounds are 4,4'-bis(dimethylamino)benzophenone,4,4'- bis(diethylamino)-benzophenone, 4,4'-bis(dibutylamino)benzophenone,4,4'-diaminobenzophenone,4,4'- dimethoxybenzophenone, 2,2',3,3'-tetramethylbenzophenone, and 4-dimethylamino-benzophenone. Especially preferred aromatic ketone compounds are those of the above general formula in which each of R1 and R2 is an amino, alkylamino or dialkylamino group.

The amount of the aromatic ketone compound used is 0.05 to 10 moles, preferably 0.2 to 2 moles, per mole of the alkali metal-based catalyst used to produce a diene polymer having an alkali metal bonded to its ends or the akali metal-based catalyst used to introduce an alkali metal into the unsaturated polymer rubber. Since the reaction of the aromatic ketone with the active polymer rubber having an alkali metal terminal or the unsaturated polymer rubber having an alkali metal added thereto takes piace rapidly, the reaction temperature and time can be selected from wide ranges. Generally, the reaction temperature is from room temperature to 100"C, and the reaction time is from several seconds to several hours.

The reaction is carried out by contacting the alkali metal-containing unsaturated polymer rubber with the aromatic ketone compound. Specifically, there can be recommended as preferred embodiments a method in which the diene-type polymer rubber is produced by polymerization with an alkali metal-based catalyst, and after the polymerization reaction is completed, a predetermined amount of the aromatic ketone compound is added to the resulting polymer rubber solution, and a method in which after an alkali metal addition reaction in the unsaturated polymer rubber solution is over, a predetermined amount of the aromatic ketone compound is subsequently added to the solution. The mode of the reaction, however, is not limited to these specific embodiments.

After the reaction, the modified unsaturated polymer rubber is isolated from the reaction solution. For this purpose, coagulating methods used in the production of rubber by usual solution polymerization, for example the addition of a coagulating agent, or steam stripping, can be used, and there is no particular restriction on the coagulating temperature. The crumb separated from the reaction mixture can be dried by using devices normally used in the production of synthetic rubbers, for example a band dryer or an extrusion-type dryer. The drying temperature is not restricted, either.

The resulting modified unsaturated polymer rubber has much improved rebound, and is therefore very useful as a rubber material for tire treads which permit low fuel costs.

The following examples specifically illustrate the present invention.

Example I A 2-liter stainless steel polymerization reactor was washed, dried, purged with dry nitrogen, and then charged with 150 g of 1,3-butadiene, 820 g of benzene, 0.5 millimole of diethylene glycol dimethyl ether (diglyme), and 1.3 millimoles of n-butyllithium (as an n-hexane solution). While the contents were stirred, 1 ,3-butadiene was polymerized at 40"C for 1 hour. When the polymerization reaction was completed, each of the compounds shown in Table 2 was added, and the mixture was stirred for 5 minutes. Then, the polymer solution in the polymerization reactor was taken out into a 1.5 % by weight methanol solution of 2,6-di-t-butyl-p-cresol (BHT) to coagulate the resulting polymer.The polymer was dried at 600C for 24 hours under reduced pressure, and its Mooney viscosity was measured.

A benzene solution of BHT was added to the polymer solution which had been reacted with each of the compounds shown in Table 2 in the same way as above, so that the amount of BHTwas 1 part by weight per 100 parts by weight of the polymer solids. With stirring, the mixture was coagulated with steam at 105"C for 1 hour. After removing water, the coagulated product was dried with hot air at 80"C for 3 hours.

The vinyl content of the polymer was measured by a conventional infrared spectral analyzing method.

The polymer rubber of Run No. 14 (comparison) was obtained by adding methanol when the polymerization reaction was completed, stirring the mixture for 5 minutes, adding 4,4'bis(dimethylamino)benzophenone, further stirring the mixture for 5 minutes, and then performing the same coagulation and drying as above.

Each of the polymers so obtained was kneaded on a roll mill with the compounding ingredients in accordance with the compounding recipe shown in Table 1. The rubber compound was then press-cured at 1600C for 25 minutes.

The rebound of the vulcanized rubber was measured at 530C by a Dunlop Tripsometer. The wet skid resistance of the vulcanized rubber was measured at 25"C by a portable skid tester made by Stanley Company using a road surface (ASTM E303-74, outdoor use type B, black, safety walk, made by 3M Company).

The results are shown in Table 2.

TABLE 1 Compounding recipe Polymer 100 parts by weight HAF carbon black 50 Aromatic process oil 5 Zinc oxide 3 Stearic acid 2 Sulfur 1 N-oxydiethylene-2-benzothiazole sulfenamide 2 TABLE 2

Amount (mmoles) Mooney Vinyl Rebound Wet skid Run No. Aromatic ketone compound of the Coagulations visco- content resistance ketone drying methods sity compound (mole) (%) 1 4,4'-bis(dimethylamino)benzophenone 0.8 Methanol/vacuum 69.0 70 67 78 2 ditto 0.8 Steam/hot air 72.5 70 67 78 3 ditto 3.0 Steam/hot air 73.0 70 67 78 4 4,4'-bis(diethylamino)benzophenone 3.0 Methanol/vacuum 69.0 70 64 78 5 ditto 3.0 Steam/hot air 73.0 70 64 78 6 4,4'-diaminobenzophenone 3.0 Methanol/vacuum 69.0 71 63 78 7 ditto 3.0 Steam/hot air 73.0 71 63 78 8 4,4'-bis(dimethylamino)benzothio- 0.8 Methanol/vacuum 69.0 70 67 78 phenone 9 ditto 0.8 Steam/hot air 75.5 71 62 78 10 ditto 3.0 Methanol/vacuum 69.0 72 67 78 11 ditto 3.0 Steam/hot air 77.0 72 62 78 12 Methanol 50 Methanol/vacuum 77.0 73 56 79 13 ditto 50 Steam/hot air 78.5 73 56 78 14 Methanol 50 Methanol/vacuum 75.0 72 56 78 4,4'-bis(dimethylamino)benzophenone 0.8 15 None - Methanol/vacuum 77.0 72 56 78 16 None - Steam/hot air 79.0 72 56 78 It is seen from the results shown in Table 2 that the modified polymers in accordance with this invention had markedly improved rebound without a reduction in wet skid resistance even when the method of coagulation and the method of drying were charged.

With the comparative polymers modified with the aromatic thioketone, the same effect as in the present invention could be obtained when coagulation and drying were carried out with a mild heat history, but the effect of improving rebound decreased when the polymers underwent a rigorous heat history during steam coagulation and hot air drying.

Example 2 The same polymerization reaction as in Example 1 was carried out except that the amount of diethylene glycol dimethyl ether (diglyme) was varied as shown in Table 3.

When the polymerization was completed, 3 millimoles of 4,4'-bis(dimethylamino)benzophenone or 50 millimoles of methanol was added, and the mixture was stirred for 5 minutes. Then, in the same way as in Example 1, the polymer was coagulated with methanol, and dried under reduced pressure.

The properties of the polymer were as shown in Table 3.

TABLE 3

Amount Wet Amount Vinyl Wet Run No. Diglyme Compound (moles) Mooney cont- Re- skid (moles) added ofthe visco- ent bound resist compound sity (mole%) (%) ance 4,4'-bis (dimethyl 17 0.29 amino)- 3 70 63 65 74 benzophenone C a) C 18 0.36 ditto " 71 68 65 76 19 0.53 ditto " 68 75 64 78 C o' 20 0.29 Methanol 50 69 63 57 74 Co n 21 0.36 ditto I 69 68 57 76 E o o 22 0.53 ditto " 67 75 56 78 It is seen from Table 3 that with polybutadiene having varying vinyl contents, the same degree of rebound improving effect as in Example 1 was noted.

Example 3 A 2-liter stainless steel polymerization reactor was washed, dried, and then charged with 65g of polybutadiene having a Mooney viscosity of 40 and a vinyl content of 70 mole% and 650 g of dehydrated n-heptane. The mixture was stirred to form a solution. Then, 2.3 millimoles of n-butyllithium (as an n-hexane solution) and 2.3 millimoles of tetramethylethlenediamine were added, and the reaction was carried out at 70"C for 1 hour. Then, 4,4'-bis(dimethylamino)benzophenone was added, and the mixture was stirred for 5 minutes. The polymer was coagulated with methanol and dried under reduced pressure in the same way as in Example 1.

The properties of the polymers were evaluated, and the results are shown in Table 4.

TABLE 4 Mooney Rebound Wet kid Run No.

viscosity ( /0) resistance After Invention 23 modifi- 58 60 78 cation Before Comparison 24 modifi- 40 56 78 cation Example 4 A 2-liter stainless steel polymerization reactor was washed, dried, purged with dry nitrogen, and charged with 112.5 g of 1,3-butadiene, 37.5 g of styrene, 820 g of benzene, 0.75 g of tetrahydrofuran and 2.0 millimoles of n-butyllithium (as an n-hexane solution). While the contents were stirred, 1,3-butadiene and styrene were polymerized at 45"C for 2 hours. When the polymerization reaction was completed, 3.0 millimoles of 4,4'-bis(dimethylamino)benzophenone was added. The mixture was stirred for 5 minutes, and the polymer was coagulated with steam and dried with hot air in the same way as in Example 1.

A comparative sample was prepared in the same way as above except that 50 millimoles of methanol was added instead of 4,4'-bis(dimethylamino)benzophenone when the polymerization reaction was terminated.

The two polymers were each compounded and vulcanized and evaluated in the same way as in Example 1 The results are shown in Table 5.

TABLE 5 Mooney Vinyl Styrene West kid Run No. Compound visco- content content Rebound resist sity (mole%) {wit. O/oj (O/oJ ance 4,4'-bis (dimethyl Invention 25 amino)- 60 35.5 24.9 65 75 benzophenone Comparison 26 Methanol 58 36.0 24.8 59 75 Examples The same reaction as in Example 3 was carried out except that polybutadiene having a Mooney viscosity of 42.0 and a cis-1 4 content of 98 mole % was used. The polymer was coagulated with methanol and dried under reduced pressure in the same way in Example 1. The results of evaulation are shown in Table 6.

TABLE 6 Run No. Mooney viscosity Rebound (%) Invention 25 After modification 45 66 Comparison 26 Before 42 60 modification

Claims (7)

1. A method of modifying an unsaturated polymer rubber, which comprises reacting an alkali metal-containing unsaturated polymer rubber with an aromatic ketone compound of the general formula

wherein R1 and R2 independentiy represent a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy group, an amino group, an alkylamino group, a dialkyiamino group or a halogen atom, and m and n independently represent an integer of from 1 to 5.

2. A method according to claim 1 wherein the alkali metal-containing unsaturated polymer rubber is an alkali metal-terminated diene-type polymer rubber obtained by polymerizing a conjugated diene monomer using an alkali metal-based catalyst.

3. A method according to claim 1 wherein the alkali metal-containing unsaturated polymer is an alkali metal-added unsaturated polymer rubber obtained by reacting an unsaturated polymer rubber with an alkali metal-containing compound.

4. A method according to claim 3 wherein the alkali metal-added unsaturated polymer rubber is an alkali metal adduct of a diene-type polymer rubber.

5. A method according to claim 3 wherein the alkali metal-added unsaturated polymer rubber is an alkali metal adduct of a ring-opened cyclo-olefin polymer rubber.

6. A method according to claim 1 substantially as described in any one of the Examples.

7. Use of a modified rubber obtained by a method as claimed in any one of the preceding claims in an automobile tire tread.