MXPA99008834A - Lime-based catalyst system - Google Patents

Abstract

The process and catalyst system of this invention can be used to synthesize a highly randomized styrene butadiene rubber with a high transmediant solution polymerization content. This styrene-butadiene rubber prepared by the process of this invention can be used in rubbers for the bearing surface of the rims that has better wear characteristics. This invention more specifically discloses a catalyst system for use in isothermal polymerizations which consists mainly of: (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide. The subject of the invention further describes a process for synthesizing a random styrene-butadiene rubber with a low vinyl content by a process consisting in copolymerizing styrene and 1,3-butadiene under isothermal conditions in an organic solvent, in the presence of a system catalyst consisting mainly of: (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide. It is also possible to add an amine to the catalyst system to increase Mooney viscosity molecular weight)

Description

CALCIUM BASED CATALYST SYSTEM BACKGROUND OF THE INVENTION It is highly desirable that pneumatic tires have good wet skid resistance, low rolling resistance and good wear characteristics. Traditionally it has been very difficult to improve - the wear characteristics of a tire without sacrificing its resistance to wet skidding and traction characteristics. These properties depend, to a certain extent, on the dynamic viscoelastic properties of the rubbers that are used in the manufacture of the rim. In order to reduce the rolling resistance and improve the wear characteristics of the tire tread, rubbers with a high bounce have usually been used in the manufacture of rubber compounds for the surface of tire rolling. On the other hand, in order to increase the resistance to wet skidding of a tire, rubbers suffering from a large energy loss have generally been used on the rolling surface of the tires. To balance these two inconsistent viscoelastic properties, mixtures of different types of synthetic and natural rubbers are normally used on the bearing surfaces of the tires.

For example, some mixtures of styrene-butadiene rubber and polybutadiene rubber are commonly used as a rubbery material for automotive tire bearing surfaces. It is generally considered desirable that the styrene-butadiene rubber used in the compounds for the bearing surface of the rim have a high level of vinyl content (microstructure 1,2-). It is also generally desirable that the repeating units derived from the styrene be randomly distributed in the polymer chains of the rubber. To achieve these objectives, styrene-butadiene rubbers are often synthesized by solution polymerization carried out in the presence of one or more modifying agents. These modifying agents are well known in the art and in general are ethers, tertiary amines, chelating ethers or chelating amines. Tetrahydrofuran, tetramethylethylene diamine (TMEDA) and diethyl ether are some representative examples of the modifying agents that are commonly used. U.S. Patent No. 5,284,927 discloses a process for preparing styrene, isoprene and butadiene terpoly rubber with multiple glass transition temperatures and with an excellent combination of properties for use in the manufacture of tire bearing surfaces, which consists of terpolymerize styrene, isoprene and 1,3-butadiene in an organic solvent at a temperature not higher than about 40 ° C, in the presence of (a) tripiperidino phosphine oxide, (b) an alkali metal alkoxide and (c) a compound organolithium U.S. Patent 5,534,592 describes a process for the preparation of polybutadiene rubber with a high content of vinyl, which consists in polymerizing 1,3-butadiene monomer with a lithium initiator at a temperature that is within the range of about 5 ° C to 100 ° C, in the presence of a sodium alkoxide and a polar modifier, wherein the molar ratio of the sodium alkoxide to the polar modifier is within the range of about 0.1: 1 to about 10: 1; and wherein the molar ratio of the sodium alkoxide to the lithium initiator is within the range of from about 0.01: 1 to about 20: 1. U.S. Patent 5,100,965 describes a process for the synthesis of a polymer with a high content of the trans structure, which consists in adding (a) at least one organolithium initiator, (b) an organoaluminum compound, (c) an alkoxide of barium and (d) a lithium alkoxide, in a polymerization medium that is composed of an organic solvent and at least one conjugated diene monomer. The United States Patent 5, 100,965 further discloses that polymers with high trans content can be used to improve the characteristics of rubber compounds for the tire tread surface. By using polymers with high trans content in the rubber compounds for the bearing surface of the rims, it is possible to manufacture rims that have better wear characteristics, resistance to tearing and operation at low temperature. These polymers with high trans content include trans-1,4-polybutadiene, trans-styrene-isoprene-butadiene terpolymers, isoprene-butadiene copolymers and trans-styrene-butadiene copolymers. U.S. Patent Application Serial No. 09 / 072,492, filed May 4, 1998, describes a process for the synthesis of a styrene-butadiene random rubber with a high trans content by a process consisting of copolymerizing styrene and 1, 3-butadiene under isothermal conditions in an organic solvent, in the presence of a catalyst system consisting mainly of: (a) an organolithium compound, (b) a barium alkoxide and (c) a lithium alkoxide.

SUMMARY OF THE INVENTION This invention is based on the unexpected discovery that a catalyst system consisting of (a) an organometallic compound of a metal selected from the group consisting of lithium, potassium, magnesium, sodium, aluminum, zinc and tin, ( b) a calcium compound and (c) a lithium alkoxide, will catalyze the copolymerization of the 1,3-butadiene monomer and the styrene monomer in a styrene-butadiene copolymer with a random distribution of repeating units that is derived from styrene. The styrene-butadiene rubber made using the catalyst system and the techniques of this invention is highly useful in the preparation of rubber compounds for tire rolling surfaces which exhibit better wear characteristics. It is preferred that the organometallic compound is a lithium, potassium, magnesium or sodium compound. Organolithium compounds are usually most preferred. Typically, the calcium compound will be a calcium carboxylate, a calcium phenolate, a calcium amine, a calcium amide, a calcium halide, a calcium nitrate, a calcium sulfate, a calcium phosphate or a calcium phosphate. calcium alcoholate. It is preferred that the calcium compound be soluble in the organic solvent used as the polymerization medium. Accordingly, it is preferred that the calcium compound is calcium alcoholate, a calcium carboxylate or a calcium phenolate. It is usually more preferred that the calcium compound be a calcium alcoholate (a calcium alkoxide). It is also possible to use calcium compounds that are insoluble in the organic solvent used as the polymerization medium. However, these calcium compounds will usually be preformed by mixing them with the other components of the catalyst in the presence of a conjugated diene monomer, such as 1,3-butadiene or isoprene. The polymerizations of this invention are usually carried out in the absence of organoaluminum compounds. A highly preferred catalyst system for the copolymerization of 1,3-butadiene monomer and styrene monomer consists mainly of: (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide. The present invention, therefore, specifically describes a catalyst system consisting mainly of: (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide. The subject of the invention further describes a process for the synthesis of a styrene-butadiene random rubber with a high trans content by a process consisting of copolymerizing styrene and 1,3-butadiene under isothermal conditions in an organic solvent in the presence of a catalyst system consisting mainly of: (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide. The subject matter of the invention also manifests a process for the synthesis of trans polybutadiene rubber having a vinyl content which is within the range of about 5% to about 15% by a process consisting of polyricing 1,3-polybutadiene in a organic solvent, in the presence of a catalyst system consisting mainly of: (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide. The present invention furthermore discloses a catalyst system consisting mainly of: (a) an organometallic compound of a metal selected from the group consisting of lithium, potassium, magnesium, sodium, aluminum, zinc and tin, (b) a calcium compound and (c) a lithium alkoxide. The invention further discloses a styrene-butadiene rubber which is particularly useful in compounds for tire rolling surfaces, the styrene-butadiene rubber being composed of repeat units which are derived from about 3% by weight to about 50% by weight. weight of styrene and from about 50% by weight to about 97% by weight of butadiene, wherein at least 98% of the repeat units derived from styrene are in blocks containing less than 5 repeat units, wherein at least 40% of the repeat units derived from styrene are in blocks containing only one styrene unit of repetition, wherein the rubber has a trans content that is within the range of 50% to 80%, wherein the rubber has a cis content that is within the range of 10% to 45%, wherein the rubber has a content of vinyl that is within the range of 5% to 20%, and where there are no segments of at least 100 repeating units within the rubber having a styrene content that differs from the total styrene content of the rubber by not more than 10%. %.

DETAILED DESCRIPTION OF THE INVENTION The polymerizations of the present invention will normally be carried out in a hydrocarbon solvent which may be one or more aromatic, paraffinic or cycloparaffinic compounds. These solvents will normally contain from 4 to 10 carbon atoms per molecule and will be liquid under the conditions of polymerization. Some representative examples of suitable organic solvents include pentane, isooctane, cyclohexane, methylcyclohexane, isohexane, n-heptane, n-octane, n-hexane, benzene, toluene, xylene, ethylbenzene, diethylbenzene, isobutylbenzene, petroleum ether, kerosene, alcohols of petroleum, petroleum naphtha and the like, alone or in mixtures.

In the solution polymerizations of this invention, usually from 5 to 30% by weight of monomers will be in the polymerization medium. These polymerization media are, of course, organic solvent and monomer compounds. In most cases, it will be preferable that the polymerization medium contains 10 to 25% by weight of monomers. It will generally be more preferred that the polymerization medium contains from 15 to 20% by weight of monomers. The styrene-butadiene rubbers in solution prepared using the catalyst system and the technique of this invention are composed of repeating units derived from 1,3-butadiene and styrene. These styrene-butadiene rubbers will usually contain from about 5% by weight to about 50% by weight of styrene and from about 50% by weight to about 95% by weight of 1,3-butadiene. However, in some cases the amount of styrene included will be as low as about 3% by weight. The styrene-butadiene rubber will most commonly contain from about 10% by weight to about 30% by weight of styrene and from about 70% by weight to about 90% by weight of 1,3-butadiene. Preferably, the styrene-butadiene rubber will contain from about 15% by weight to about 25% by weight of styrene and from about 75% by weight to about 85% by weight of 1,3-butadiene. These styrene-butadiene rubbers will usually have a melting point in the range of about -10 ° C to about -20 ° C. Styrene-butadiene copolymer resins containing from about 50% by weight to about 95% by weight of styrene and from about 5% by weight to about 50% by weight of 1,3-butadiene can also be synthesized using the systems catalysts of this invention. These copolymers with glass transition temperatures within the range of 7 ° C to 70 ° C can be used as resinous or organic pigment. In the styrene-butadiene rubbers of this invention, the distribution of the repeat units from styrene and butadiene is practically random. The term "random" or random as used herein means that less than 5% of the total amount of the repeat units derived from styrene are in blocks containing 5 or more styrene repeat units. In other words, more than 95% __ of the repeating units derived from styrene are in blocks containing less than 5 repeating units. A large number of repeating units derived from styrene will be in blocks containing only one μN of styrene repeat. These blocks containing a repeat unit of styrene are joined on both sides by repeating units that come from 1,3-butadiene. In styrene-butadiene rubbers containing less than about 30% by weight of bound styrene that are made with the catalyst system of this invention, less than 2% of the total amount of the repeat units derived from styrene are in blocks that contain 5 or more styrene repeat units. In other words, more than 98% of the repeat units derived from styrene are in blocks containing less than 5 repeating units. In these styrene-butadiene rubbers, more than 40% of the repeat units derived from styrene will be in blocks containing only one styrene repeat unit, more than 75% of the repeat units derived from styrene will be in blogs containing less than 3 repetition units and more 90% of the repeat units derived from styrene will be in blocks containing less than 4 repeating units. In styrene-butadiene rubbers containing less than about 20% by weight of bound styrene, which are prepared with the catalyst system of this invention, less than 1% of the total amount of the repeat units derived from styrene are in blocks containing 4 or more styrene repeat units. In other words, more than 99% of the repeating units derived from styrene are in blocks containing less than 4 repeating units. In these styrene-butadiene rubbers, more than 60% of the repeat units derived from styrene will be in blocks containing only one styrene repeat unit and more than 90% of the styrene-derived repeat units will be in blocks containing less than 3 repeat units. The styrene-butadiene copolymers of this invention also have a consistent composition along their polymer chains. In other words, the styrene content of the polymer will be the same from the beginning to the end of the polymer chain. None of the segments of at least 100 repeating units within the polymer will have a styrene content that differs from the total styrene content of the polymer by more than 10%. These styrene-butadiene copolymers will usually not contain segments with a length of at least 100 repeating units having a styrene content that differs by more than about 5% of the total styrene content of the polymer. The polymerizations of this invention are initiated by adding (a) an organometallic compound of a metal selected from the group consisting of lithium, potassium, magnesium, sodium, aluminum, zinc and tin, (b) a calcium compound and (c) an alkoxide of lithium to a polymerization medium containing the monomers to be polymerized. The polymerizations of this invention are usually initiated by adding an organolithium compound, a calcium alkoxide and a lithium alkoxide to a polymerization medium containing the monomers styrene and 1,3-butadiene. Such polymerization can be carried out using batch, semi-continuous or continuous techniques. The organolithium compounds that can be employed in the process of this invention include the types of monofunctional and multifunctional initiator known to polymerize the conjugated diolefin monomers. The multifunctional organolithium initiators can be the specific organolithium compounds or they can be multifunctional types which are not necessarily specific compounds but instead represent reproduced compositions of controlled functionality. The choice of the initiator can be according to the degree of branching and the desired degree of elasticity for the polymer, the nature of the feedstock and the like. With respect to the feedstock employed as the source of conjugated dienes, for example, types of multifunctional initiators are generally preferred when a stream of low concentration dienes is at least a portion of the feedstock, since some components present in the Low concentration, non-purified dienes stream may tend to react with the carbon lithium bonds to deactivate the organolithium compound activity, thus necessitating the presence of sufficient lithium functionality to overcome these effects. The multifunctional organolith compounds that can be used include those that are prepared by the reaction of an organomonolithium compound with a multivinylphosphine or a ultivinylsilane, carrying out the reaction preferably in an inert diluent such as a hydrocarbon or a mixture of a hydrocarbon and a polar organic compound. The reaction between the multivinylsilane or multivinylphosphine and the organomonolithium compound can give rise to a precipitate which can be solubilized, if desired, by the addition of a solubilizing monomer such as a conjugated diene or a monovinylaromatic compound, after the reaction of the primary components. Otherwise, the reaction can be carried out in the presence of a minor amount of the solubilizing monomer. The relative amounts of the organomonolithium compound and the multivinylsilane or multivinylphosphine preferably should be in the range of about 0.33 to 4 moles of the organomonolithium compound per mole of vinyl groups present in the multivinylsilane or multivinylphosphine employed. It should be noted that these multifunctional initiators are commonly used as mixtures of compounds instead of as specific individual compounds. Exemplary organomonolithium compounds include ethyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, tert-octyl lithium, n-eicosyl lithium, phenyl lithium, 2-naphthyl lithium, 4-butyl phenyl lithium, 4-phenyl tolyl lithium , 4-phenyl butyl lithium, cyclohexyl lithium and the like. Exemplary multivinylsilane compounds include tetravinylsilane, methyl trivinylsilane, diethyldivinylsilane, di-n-dodecyldivinylsilane, cyclohexyltrivinylsilane, phenyltrivinylsilane, benzyltrivinylsilane, (3-ethylcyclohexyl) 3-n-butylphenyl) divinylsilane and the like. Exemplary multivinylphosphine compounds include trivinylphosphine, methyldivinylphosphine, dodecyldivinylphosphine, phenyldivinylphosphine, cyclooctyldivinylphosphine and the like. Other multifunctional polymerization initiators can be prepared using an organomonolithium compound, together with a multivinyl aromatic compound and a conjugated diene or an aromatic monovinyl compound or both. These ingredients can be charged initially, usually in the presence of a hydrocarbon or a mixture of a hydrocarbon and a polar organic compound as a diluent. Otherwise, a multifunctional polymerization initiator can be prepared in a two-step process by reacting the organomonolithium compound with a conjugated diene or additive monovinyl aromatic compound and then adding the multivinyl aromatic compound. Any of the conjugated dienes or mono vinyl aromatic compounds described can be employed. The ratio of the conjugated diene or monovinyl aromatic compound preferably used should be in the range of about 2 to 15 moles of the polymerizable compound per mole of the organolithium compound. The amount of aromatic multivinyl compound used preferably should be in the range of about 0.05 to 2 moles per mole of organomonolithium compound. Exemplary multivinyl aromatic compounds include: 1,2-divinylbenzene, 1,3-divinylbenzene, 1,4-divinylbenzene, 1, 2,4-trivinylbenzene, 1,3-divinylnaphthalene, 1,8-divinylnaphthalene, 1, 3, 5 -trivinylnaphthalene, 2,4-divinyldiphenyl, 3, 5, '-trivinyldiphenyl, m-diisopropenylbenzene, p-diisopropenylbenzene, 1,3-divinyl-4, 5, 8-tributylnaphthalene and the like. Divinyl aromatic hydrocarbons containing up to 18 carbon atoms per molecule are preferred, particularly divinyl benzene as the ortho, meta or para isomer, and commercial divinyl benzene which is a mixture of the three isomers, and other compounds such as ethylstyrene, is also very satisfactory. Other types of multifunctional lithium compounds can be employed as the preparations by contacting a compound-organometallithium compound with 1,3-butadiene in a proportion of about 2 to 4 moles of the organomonolithium compound per mole of 1, 3- butadiene, in the absence of polar material added in this case, being the preferred contact made in an inert hydrocarbon diluent, although, if desired, the contact can be used without the diluent. Otherwise, specific organolithium compounds can be employed as initiators, if desired, in the preparation of polymers according to the present invention. These can be represented by R (Li) x wherein R represents a hydrocarbyl radical containing from 1 to 20 carbon atoms, and wherein x is an integer from 1 to 4. The exemplary organolithium compounds are methyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, tert-octyl lithium, n-decyl lithium, phenyl lithium, 1-naphthyl lithium, 4-butyl phenyl lithium, 4-butyl phenyl lithium, p-tolyl lithium, 4-phenylbutyl lithium, cyclohexyl lithium, 4-butylcyclohexyl lithium, 4-cyclohexyl butyl lithium, dilithiomethane, 1,4-dilithium butane, 1, 10-dilithiodecane, 1,20-dilithium eicosane, 1,4-dilithio cyclohexane, 1, -dilithium-2- butane, 1, 8-dilithio-3-decene, 1,2-dilithio-l, 8-diphenyloctane, 1,4-dilithiobenzene, 1,4-dilithio naphthalene, 9,10-dilithium anthracene, 1,2-dilithium -l, 2-diphenyl ethane, 1, 3, 5-trilithium pentane, 1, 5, 15-trilithio eicosane, 1, 3, 5-trilithio cyclohexane, 1, 3, 5, 8-tetralithium decane, 1, 5, 10, 20-tetralithium eicosane, 1, 2, 4, 6-tetralithio cyclohexane, 4, 4'-dithio biphenyl and the like. The calcium alkoxides that can be used usually have the structural formula: R1-0-Ca-0-R2 wherein R1 and R2 may be the same or different and represent alkyl groups (including cycloalkyl groups), aryl groups, alkaryl groups, arylalkyl groups. Some representative examples of suitable calcium alkoxides include calcium dimethoxide, calcium diethoxide, calcium diisopropoxide, calcium di-n-butoxide, calcium di-sec-butoxide, calcium di-t-butoxide, di (1.1). -dimethylpropoxide) of calcium, calcium di (1,2-dimethylpropoxide), calcium di (1,1-dimethylbutoxide), calcium di (1, 10-dimethylpentoxide), di (calcium 2-ethylhexanoxide, di Calcium (1-methylheptoxide), calcium di (p-methylphenoxide), calcium di (p-methylphenoxide), calcium di (p-octylphenoxide), calcium di (p-nonylphenoxide), di (p-dodecylphenoxide) of calcium, calcium di (a-naphthoxide), calcium di (β-naphthoxide), calcium (o-methoxyphenoxide), calcium di (m-methoxyphenoxide), calcium di (p-methoxyphenoxide), (o- ethoxyfenoxide) of calcium, calcium (4-methoxy-l-naphthoxide) and the like Cyclic compounds, such as calcium ditetrahydrofurfurilate can also be used in the catalyst system. be prepared using inexpensive initial materials with a relatively simple procedure. This is done by the reaction of calcium hydroxide, Ca (0H) 2, with an alcohol of the formula ROH at a temperature within the range of about 150 ° C to 250 ° C. This reaction can be represented as follows: Ca (0H) 2 + 2 ROH? Ca (OR) 2 + 2 H20 wherein R represents an alkyl group, an aryl group or an alkaryl group. R is preferably a 2-ethylhexyl group, a nonyl phenyl group, a dodecyl phenyl group, a tetrahydrofurfuryl group or a furfuryl group. This reaction will preferably be carried out at a temperature that is within the range of about 175 ° C to 200 ° C with the alcohol acting as the solvent for the reaction. The reaction will usually be at a temperature above the boiling point of the alcohol for a period of 2 to 3 hours. After the reaction is over, the excess alcohol is removed by vacuum distillation or evaporation. Then, the calcium alkoxide is recovered by dissolving it in a suitable organic solvent, such as ethylbenzene, toluene or xylene. The lithium alkoxide compounds that can be used have the structural formula: LiOR wherein R represents an alkyl group, an aryl group, an alkaryl group, an arylalkyl group or a hydrocarbon group containing at least one heteroatom selected from the group consisting of oxygen atoms and nitrogen atoms. The lithium alkoxide can be synthesized by reacting an organolithium compound, lithium metal or lithium hydride with an alcohol. The organolithium compound, metal or lithium hydride can react with the alcohol in a molar ratio of 0.5: 1 to 3: 1. It is preferred that the alcohol reacts with an equimolar amount of the organolithium compound, the lithium metal or lithium hydrides. Some representative examples of alcohol that can be used in the preparation of the lithium alkoxide include: methanol, ethanol, n-propyl alcohol, isopropyl alcohol, t-butanol, sec-butanol, cyclohexanol. octanol, 2-ethylhexanol, p-cresol, m-cresol, nonyl phenol, hexylphenol, tetrahydrofurfuryl alcohol, furfuryl alcohol, 3-methyltetrahydrofurfuryl alcohol, tetrahydrofurfuryl alcohol oligomer, ethylene glycol monophenyl ether, ethylene glycol monobutyl ether, N, N-dimethylethanolamine , N, N-diethylethanolamine, N, N-dibutylethanolamine, N, N-diphenylethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-butyldiethanolamine, N-phenyldiethanolamine, N, N-dimethylpropanolamine, N, N-dibutylpropanolamine, N-methyldipropanolamine, N-ethyldipropanolamine, 1- (2-hydroxyethyl) pyrrolidine, 2-methyl-1- (2-hydroxyethyl) pyrrolidine, 1-piperidinetanol, 2-phenyl-1-piperidinetanol, 2-ethyl-1-piperidinepropanol, N-β- hydroxyethylmorpholine, 2-ethyl-N-8-hydrosxyethylmorpholine, 1-piperazinetanol, 1-piperazinepropanol, N, N'bis (β-hydroxyethyl) piperazine, N, N'-bis (Y-hydroxypropyl) piperazine, 2- (β-hydroxyethyl) pyridine, 2- (α-hydroxypropyl) pyridine and the like. The molar ratio of lithium alkoxide to calcium alkoxide will be within the range of about 1: 1 to about 20: 1 and preferably will be within the range of 5: 2 to 10: 1. The molar ratio of lithium alkoxide to calcium alkoxide most preferably will be within the range of about 3: 1 to about 5: 1. The molar ratio of the alkyl lithium compound to calcium alkoxide will be within the range of about 1: 1 to about 6: 1 and preferably will be within the range of 3: 1 to 4: 1. The molar ratio of the alkyl lithium compound to the most preferred calcium alkoxide will be within the range of 2: 1 to 3: 1. The organolithium compound will normally be present in the polymerization medium in an amount within the range of about 0.01 to 1 phm (parts per hundred parts by weight of the monomer). In most cases, from 0.01 phm to 0.1 phm of the organolithium compound will be used, it being preferred to use 0.025 phm to 0.07 phm of the organolithium compound in the polymerization medium. The polymerization temperature used can vary over a wide range of temperatures from about 20 ° C to about 180 ° C. In most cases, a temperature in the range of about 40 ° C to about 120 ° C will be used. Usually, it is more preferred that the polymerization temperature be within the range of about 70 ° C to about 100 ° C. The pressure used will normally be sufficient to maintain a substantially liquid phase under the conditions of the polymerization reaction. It is possible to use polar modifiers to modify the micro structure of the rubbery polymer that is going to be synthesized. The ethers and amines that act as Lewis bases are representative examples of the polar modifiers that can be used. Some specific examples of common polar modifiers include: diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dimethyl ether, trimethylamine, triethylamine, N, N, N ', N' -tetramethylethylenediamine (TMDEA), N-methylmorpholine, N-ethylmorpholine, N-phenylmorpholine and the like dipiperidinoethane, dipyrrolidinoethane, tetramethylethylenediamine, diethylene glycol, dimethyl ether, TMEDA, tetrahydrofuran , piperidine, pyridine and hexamethyl ina are representative of the highly preferred modifiers. U.S. Patent 4,022,956 describes the use of tertiary ethers and amines as polar modifiers in greater detail. The polymerization is carried out for a sufficient time to allow the polymerization of the monomers practically complete. In other words, polymerization is usually carried out until high conversions are obtained. Then, the polymerization can be terminated using standard techniques. The polymerization can be terminated with a conventional type of non-copulant terminator (such as water, an acid and a lower alcohol) or with a coupling agent. The coupling agents can be used to improve the cold flow characteristics of the rubber and the rolling resistance of the tires manufactured from them. This also gives rise to better processing capacity and other beneficial properties. It is possible to employ a wide variety of suitable compounds for these purposes. Some representative examples of suitable coupling agents include: multivinyl aromatic compounds, multi-epoxies, multiisocyanates, multiimines, multialdehydes, ulticetonates, ulthalides, mulanhydrides, multiesters which are esters of polyalcohols with monocarboxylic acids, and diesters which are esters of monohydric alcohols with dicarboxylic acids , and similar. Examples of suitable multivinyl aromatic compounds include divinylbenzene, 1, 2, 4-trivinylbenzene, 1,3-divinylnaphthalene, 1,8-diynylnaphthalene, 1,3,5-trivinylnaphthalene, 2,4-divinylbiphenyl and the like. Divinyl aromatic hydrocarbons, particularly divinylbenzene, are preferred in their ortho, meta or para isomers. Commercial divinylbenzene, which is a mixture of the three isomers and other compounds, is very satisfactory. Although it is possible to use any multiepoxide, liquids are preferred since they are handled more easily and form a relatively small number for the radial polymer. Among the especially preferred multi-epoxies are the epoxidized hydrocarbon polymers such as epoxidized liquid polybutadienes and epoxidized vegetable oils such as epoxidized soybean oil and epoxidized linseed oil. It is also possible to use other epoxy compounds, such as 1,2,5,6,9, 10-triepoxydecane. Examples of suitable multiisocyanates include benzene-1, 2, 4, -triisocyanate, naphthalene-1, 2, 5, 7-tetraisocyanate and the like. Especially suitable is a commercially available product known as PAPI-1, a polyaryl polyisocyanate with an average of three isocyanate groups per molecule and an average molecular weight of about 380. This compound can be visualized as a series of bound isocyanate-substituted benzene rings. through methylene bonds. The multiimines, which are also known as multiaziridinyl compounds, are preferably those containing three or more aziridine rings per molecule. Examples of these compounds include the triaziridinylphosphine oxides or sulphides such as tri (l-aryidinyl) phosphine [sic] oxide, tri (2-methyl-l-aryidinyl) phosphine oxide [sic], tri (2-) sulfide ethyl-3-decyl-l-aryridinyl) phosphine and the like. The multialdehydes are represented by compounds such as 1,4,4-naphthalenetricarboxyaldehyde, 1,7,9-anthracene tricarboxyaldehyde, 1,1,5-pentanetricarboxyaldehyde and similar multialdehydes containing aliphatic and aromatic compounds. The multicetones may be represented by compounds such as 1, 4, 9, 10-anthracenterone, 2,3-diacetoneylcyclohexanone and the like. Examples of the mutant hydrides include pyromellitic dianhydride, styrene-maleic anhydride copolymers, and the like. Examples of the multi-esters include diethyladadipate, triethyl citrate, 1,3,5-tricardetoxybenzene and the like. Preferred multihalides are silicon tetrahalides (such as silicon trichloride, silicon tetrabromide and silicon tetraiodide) and trialosilanes (such as triflurosilane, trichlorosilane, trichloroethylsilane, tribromonobenzylsilane and the like). Also preferred are hydrocarbons substituted with multihalogen (such as 1, 3, 5-tri (bromo methyl) benzene and 2,4,6,9-tetrachloro-3,7-decadiene) in which the halogen is attached to a carbon atom that is alpha for an activating group such as an ether bond, a carbonyl group or a carbon-carbon double bond. Substituents inert with respect to the lithium atoms in the termally reactive termal polymer may also be present in the active halogen-containing compounds. Otherwise, other suitable reactive groups other than halogen may be present as already described. Examples of compounds containing more than one type of functional group include: 1,3-dichloro-2-propanqna, 2,2-dibromo-3-decanone, 3,5,5-trifluoro-4-octanone, 2, 4-dibromo-3-pentanone, 1,2,4,5-diepoxy-3-pentanone, 1,2,, 5-dipoxy-3-hexanone, 1,2,11,12-diepoxy-8-pentadecanone, 1 , 3.18, 19-diepoxy-7, 14-eicosandione and the like. In addition to the silicon multihalides as described above, other metal multihalides, particularly those of tin, lead or germanium, can also be easily employed as coupling and branching agents. The difunctional counterparts of these agents can also be employed, resulting in a linear polymer rather than a branched polymer. The monofunctional counterparts can be used to crown the rubbery polymer. For example, trialkyl tin chlorides, such as triisobutyl tin chloride, can be used to crown the rubbery polymer. In a broad sense, and as an example, a range of about 0.01 to 4.5 milliequivalents of the coupling agent is employed per 100 grams of monomer. It is preferred to use about 0.01 to about 1.5 milliequivalents of the coupling agent per 100 grams of monomer to obtain the desired Mooney viscosity. Larger amounts tend to result in the production of polymers containing terminal reactive groups or insufficient coupling. An equivalent of the treatment agent per equivalent of lithium is considered an optimum amount for maximum branching, if this result is desired in the production line. The coupling agent can be added in hydrocarbon solution (for example in cyclohexane) to the polymerization mixture in the final reactor with suitable mixing for distribution and reaction. After the copolymerization has been completed, the styrene-butadiene elastomer can be recovered from the organic solvent. The styrene-butadiene rubber can be recovered from the organic solvent and the residue by means of decantation, filtration, centrifugation and the like. It is often desirable to precipitate the segmented polymer from the organic solvent by the addition of lower alcohols containing from about 1 to about 4 carbon atoms to the polymer solution. Lower alcohols suitable for precipitation of the segmented polymer from the polymer cement include methanol, ethanol, isopropanol, n-propyl alcohol and t-butyl alcohol, the use of lower alcohols to precipitate the polymer cement also "kills" the polymer latent inactivating the terminal lithium groups. After the segmented polymer is recovered from the solution it is possible to employ steam drag to reduce the level of volatile organic compounds in the rubber.

There are valuable benefits associated with the use of the styrene-butadiene rubbers of this invention in the preparation of the compounds for the tread surface of the rim. For example, the styrene-butadiene rubber of this invention can be combined with natural rubber to make compounds for the bearing surface for passenger tires that exhibit outstanding characteristics of rolling resistance, traction and wear of the bearing surface. In cases where wear of the bearing surface is of great importance, a high content of cis-1,4-polybutadiene can also be included in the mixture. In any case, the styrene-butadiene rubbers of this invention can be used to improve the traction, wear of the rolling surface and rolling resistance of the rims manufactured therewith. This invention is illustrated by means of the following examples which are merely for the purpose of illustration and are not considered as limiting the scope of the invention or the manner in which it can be applied. Unless otherwise specified, parts and percentages are given by weight.

Examples The calcium-based catalyst of this invention can be used in the homopolymerization of 1,3-butadiene in polybutadiene (PBD), in the homopolymerization of isoprene in polyisoprene (Pl), in the copolymerization of styrene and 1,3-butadiene in styrene-butadiene rubber (SBR) and in the terpolymerization of styrene, isoprene and 1,3-butadiene in styrene-isoprene-butadiene rubber (SIBR). The calcium-based catalyst system of this invention can be prepared in situ or can be preformed.

Preparation of SBR in solution A styrene / butadiene premix containing 10 percent styrene and 90 percent 1,3-butadiene was charged to a one gallon (3,785 liters) reactor equipped with a mechanical stirrer and a nitrogen blanket . Heat was applied to this reactor until the temperature of the premix reached 75 ° C. At this time, the catalyst was introduced. The catalyst included calcium tetrahydrofurfuryl alcohol (the calcium salt of the tetrahydrofurfuryl alcohol which is soluble in hexane) which was introduced at a level of 1 mmol per 100 g of monomer. This was followed by the addition of 2 mmol of n-butyl lithium and 2 mmol of lithium t-butoxide, based on 100 g of monomer. It should be noted that the catalyst can be preformed or that the catalyst components can be added individually. Samples were taken at different time intervals and analyzed by gas chromatography (GC) analysis. The data showed that the composition of monomer 30/70 in the premix (monomer plus hexane) resulted in a copoiimer with a constant composition of 30% styrene and 70% butadiene. In this way, a random copolymer was prepared through the polymerization. A monomer conversion of approximately 90% was achieved after only one hour of the polymerization time. The polymer was analyzed and determined with a glass transition temperature (Tg) of -54 ° C, a 20% content of 1,2-polybutadiene (vinyl) bound and random styrene sequences. This polymerization with the calcium-based catalyst system offers the advantage of favoring a much faster polymerization rate than can be obtained using calcium-based catalyst systems. Variations in the present invention are possible in light of the description of what is proposed herein. Although certain representative embodiments and details have been shown for the purpose of illustration of the subject of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made herein without departing from the scope of the invention. Therefore, it should be understood that the changes can be made in the specific embodiments described which will be within the full scope of the invention proposed as defined by the following appended claims.

Claims (10)

1. A catalyst system characterized in that it consists mainly of: (a) an organolithium compound, (b) a calcium alkoxide and (c) a lithium alkoxide.

2. The catalyst system as specified in claim 1 is characterized in that the molar ratio of the lithium alkoxide to the calcium alkoxide is within the range of about 1: 1 to about 20: 1; and characterized in that the molar ratio of the alkyl lithium compound to the calcium alkoxide is within the range of about 1: 1 to about 6: 1.

3. The catalyst system as specified in claim 2 is characterized in that the calcium alkoxide is selected from the group consisting of calcium dimethoxide, calcium diethoxide, calcium diisopropoxide, calcium di-n-butoxide, di-sec. -calcium butoxide, calcium di-t-butoxide, calcium di (1,1-dimethylprophoxide), calcium di (1,2-dimethylpropoxide), calcium di (1,1-dimethylbutoxide), di (1, 10-dimethylpentoxide) of calcium, di (calcium 2-ethylhexanoxide, calcium di (1-methylheptoxide), calcium di (p-methylphenoxide), calcium di (p-methylphenoxide), di (p-octylphenoxide) calcium, calcium di (p-nonylphenoxide), calcium di (p-dodecylphenoxide), calcium di (a-naphthoxide), calcium di (β-naphthoxide), calcium (o-methoxyfenoxide), di (m) -methoxyphenoxide) of calcium, calcium di (p-methoxyphenoxide), calcium (o-ethoxyphenoxide), calcium (4-methoxy-l-naphthoxide) and calcium tetrahydrofurfurylte, and is characterized because the organolithium compound is a compound or organomonolitio.

4. The catalyst system as specified in claim 3 is characterized in that the molar ratio of the lithium alkoxide to the calcium alkoxide is within the range of about 5: 2 to about 10: 1; and characterized in that the molar ratio of the alkyl lithium compound to the calcium alkoxide is within the range of about 3: 2 to about 4: 1,

5. The catalyst system as specified in claim 4 is characterized in that the alkoxide lithium is prepared by reacting an organolithium compound, lithium metal or lithium hydride with an alcohol selected from the group consisting of methanol, ethanol, n-propyl alcohol, isopropyl alcohol, t-butanol, sec-butanol, cyclohexanol, octanol, 2- ethylhexanol, p-cresol, m-cresol, nonyl phenol, hexylphenol, tetrahydrofurfuryl alcohol, furfuryl alcohol, 3-methyltetrahydrofurfuryl alcohol, oligomer of tetrahydrofurfuryl alcohol, ethylene glycol monophenyl ether, ethylene glycol monobutyl ether, N, N-dimethylethanolamine, N, N -diethylethanolamine, N, N-dibutylethanolamine, N, N-diphenylethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-butyldiethanolamine, N-phenyldiethanolamine, N, N-dimethylpropanolamine, N, N-dibutylpropane-1amine, N-methyldipropanolamine, N-ethyldipropanolamine, 1- (2-hydroxyethyl) pyrrolidine, 2-methyl-1- (2-hydroxyethyl) pyrrolidine, 1-piperidinetanol, 2-phenyl-1-piperidineethanol, 2- ethyl-l-piperidinpropanol, N-β-hydroxyethylmorpholine, 2-ethyl-N-8-hydroxyethylmorpholine, 1-piperazinetanol, 1-piperazinepropanol, N, N'bis (β-hydroxyethyl) piperazine, N, N'-bis (Y -hydroxypropyl) piperazine, 2- (β-hydroxyethyl) pyridine, 2- (α-hydroxypropyl) pyridine; and characterized in that the organolithium compound is selected from the group consisting of ethyl lithium, isopropyl lithium, N-butyl lithium, sec-butyl lithium, tert-octyl lithium, phenyl lithium, 2-naphthyl lithium, 4-butyl phenyl lithium, 4-tolyl lithium, 4-phenyl butyl lithium, cyclohexyl lithium and hexyl lithium.

6. The catalyst system as specified in claim 5 is characterized in that the molar ratio of the lithium alkoxide to the calcium alkoxide is within the range of about 3: 1 to about 5: 1.

7. The catalyst system as specified in claim 6 is characterized in that the molar ratio of the alkyl lithium compound to the calcium alkoxide is within the range of about 2: 1 to about 3: 1.

8. A process for synthesizing a random styrene-butadiene rubber with a high trans content and low vinyl content by a process that includes the copolymerization of styrene and, 3-butadiene in an organic solvent, characterized in that the copolymerization is carried out in the presence of the catalyst system specified in claim 1.

9. The process for the synthesis of a random styrene-butadiene rubber as specified in claim 8 is characterized in that about 3% by weight to about 50% by weight of styrene is copolymerized with about 50% by weight to about 97% by weight of 1,3-butadiene; it is characterized in that the copolymerization is carried out at a temperature that is within the range of about 40 ° C to about 120 ° C; and characterized in that the organolithium compound is present in an amount that is within the range of about 0.01 phm to about 0.1 phm.

10. A process for synthesizing trans polybutadiene rubber with a vinyl content that is within the range of about 5% to about 20% by a process that includes the polymerization of 1,3-butadiene in an organic solvent characterized in that the polymerization is perform in the presence of the catalyst system specified in claim 1.