USE OF A Cr- OR Mo-BASED CATALYST SYSTEM TO PRODUCE BLENDS OF SYNDIOTACTIC 1,2-POLYBUTADIENE AND RUBBERY ELASTOMERS

Abstract: Blends of syndiotactic 1,2-polybutadiene and rubbery elastomers are prepared by a process that includes polymerizing 1,3-BD monomer into syndiotactic 1,2-polybutadiene within a rubber cement of at least one rubbery elastomer by using a catalyst composition that is formed by combining a hydrogen phosphite with a Cr-containing compound and an organomagnesium compound or with a Mo-containing compound and an organoaluminum compound.

Description: USE OF A Cr- OR Mo-BASED CATALYST SYSTEM TO PRODUCE BLENDS OF SYNDIOTACTIC 1,2-POLYBUTADIENE AND RUBBERY ELASTOMERS BACKGROUND OF THE INVENTION The present invention is directed to a process for producing blends of syndiotactic 1 ,2-polybutadiene and rubbery elastomers, more particularly to a process that includes polymerizing 1,3-butadiene into syndiotactic 1 ,2-polybutadiene within a rubber cement by using a Cr- or Mo-based catalyst composition. Syndiotactic 1 ,2-polybutadiene (hereinafter "s-PBD") is a crystalline thermoplastic resin that has a stereoregular structure in which the side-chain vinyl groups are located alternately on opposite sides of the polymeric main chain. It exhibits the properties of both plastics and rubber and therefore has many uses. For example, films, fibers, and various molded articles can be made utilizing s-PBD. It also can be blended into and co-cured with natural and synthetic rubbers. s-PBD can be made by solution, emulsion, or suspension polymerization. Generally, s-PBD has a melting temperature within the range of about 195° to about 215°C but, due to processability considerations, a melting temperature of less than about 195°C generally is desirable. Because s-PBD is insoluble in common solvents at normal polymerization temperatures, a common technical difficulty synthesizing it is that the polymerization mixture is an extremely thick slurry at the commercially desirable polymer concentration of 10 to 25% by weight. This thick slurry becomes difficult to stir and transfer, thereby diminishing heat transfer efficiency and interfering with proper process control. Also, the slurry contributes to reactor fouling due to the undesirable build-up of insoluble polymer on the baffles, agitator blades, agitator shafts, and walls of the polymerization reactor. Cleaning the reactor on a regular basis is necessary, which results in frequent shutdowns of continuous processes and serious limitations on the run length of batch processes; cleaning the fouled reactor generally is difficult and time-consuming. These drawbacks detrimentally affect productivity and the cost of operation. Development of a method of synthesizing s-PBD that avoids this frequent reactor fouling problem is desirable. Transition metal catalyst systems based on Co, Ti, V, Cr, and Mo for the preparation of s-PBD have been reported. The majority of these catalyst systems, however, have little or no practical utility because they have low catalytic activity or poor stereoselectivity, and in some cases they produce low molecular weight polymers or partially crosslinked polymers unsuitable for commercial use. The following Co-based catalyst systems are known for preparing s-PBD on a commercial scale: (1) a catalyst system containing cobalt bis(acetylacetonate), triethylaluminum, water, and triphenylphosphine (U.S. Pat. Nos. 3,498,963 and 4,182,813), and (2) a catalyst system containing cobalt tris(acetylacetonate), triethyl- aluminum, and CS 2 (U.S. Pat. No. 3,778,424). These Co-based catalyst systems have serious disadvantages. The first Co catalyst system yields s-PBD having very low crystallinity. Also, this catalyst system develops sufficient catalytic activity only when halogenated hydrocarbon solvents are used as the polymerization medium, and halogenated solvents present toxicity problems. The second Co catalyst system uses CS 2 as one of the catalyst components. Because of its low flash point, obnoxious smell, high volatility, and toxicity, CS 2 is difficult and dangerous to use, and requires expensive safety measures to prevent even minimal amounts escaping into the atmosphere. Furthermore, the s-PBD produced with this Co catalyst system has a very high melting temperature of about 200° to 210°C, which makes processing the polymer difficult. Although the melting temperature of the s-PBD produced with this Co catalyst system can be reduced by employing a catalyst modifier as a fourth catalyst component, the presence of this catalyst modifier has adverse effects on the catalyst activity and polymer yields. The physical properties of rubbery elastomers can be improved by blending crystalline polymers. For example, incorporating s-PBD into rubber compositions utilized in the supporting carcass of tires greatly improves the green strength of components made from those compositions. Also, incorporating s-PBD into tire tread compositions can reduce the heat build-up and improve the wear characteristics of tires. The green strength of synthetic rubbers such as c/s-1 ,4-polybutadiene also can be improved by incorporating a small amount of s-PBD. Blends of crystalline polymers and rubbery elastomers typically are prepared by standard mixing techniques. For example, these blends can be prepared by mixing or kneading and heat-treating a crystalline polymer and a rubbery elastomer by using generally known mixing equipment. These high-temperature mixing procedures can have certain drawbacks including high processing costs, polymer degradation and crosslinking, inadequate mixing, as well as various process limitations. Due to the high vinyl content of s-PBD, polymer degradation and crosslinking is a particularly severe problem for mixing s-PBD with elastomers at high temperatures. Attempts to polymerize 1 ,3-butadiene (hereinafter "1 ,3-BD") into s-PBD within a rubber cement have been hampered by the same catalyst inefficiencies and toxicities mentioned above. For example, U.S. Pat. No. 4,379,889 teaches polymerizing 1 ,3-BD into s-PBD within a rubber cement by using a catalyst system that includes a Co compound, a dialkylaluminum halide, CS 2 , and an electron donor compound. And, U.S. Pat. No. 5,283,294 teaches a similar process that employs a catalyst system that includes a Co compound, an organoaluminum compound, and CS 2 . These methods, however, are inferior because the catalyst systems that are employed suffer from the foregoing disadvantages. Therefore, a simple and commercially viable process for producing blends of s-PBD and rubbery elastomers remains desirable. SUMMARY OF THE INVENTION In general, the present invention provides a process for preparing blends of s- PBD and rubbery elastomers. The process includes (1) providing a mixture of a rubber cement and 1 ,3-BD and (2) polymerizing the 1 ,3-BD into s-PBD within the rubber cement by using a catalyst composition that is the combination of or the reaction product of ingredients that include (a1) a Cr-containing compound, (b1) a hydrogen phosphite, and (d) an organomagnesium (hereinafter "org-Mg") compound or (a2) a Mo-containing compound, (b2) a hydrogen phosphite, and (c2) an organoaluminum (hereinafter "org-AI") compound. The present invention further provides a process for producing blends of s- PBD and rubbery elastomers. The process includes (1) providing a mixture of a rubber cement and 1,3-BD and (2) polymerizing the 1 ,3-BD into s-PBD within the rubber cement by using the above-described catalyst composition. The present invention also provides a blend of s-PBD and rubbery elastomers prepared by a process that includes (1) providing a mixture of a rubber cement and 1 ,3-BD, and (2) polymerizing the 1 ,3-BD into s-PBD within the rubber cement by using the above-described catalyst composition. Advantageously, the process of this invention directly provides blends of s- PBD and rubbery elastomers by synthesizing s-PBD within a rubber cement and thereby obviates the need for high-temperature mixing. Also, good dispersion of s- PBD throughout rubbery elastomers can be achieved easily and economically. Significantly, the process eliminates the problems of high processing costs, polymer degradation and crosslinking, inadequate mixing, and various process limitations that are associated with high-temperature mixing procedures. The process also alleviates the problems of polymer cement thickness and reactor fouling associated with the synthesis of s-PBD in the absence of a rubbery elastomer. In addition, the catalyst system employed has very high catalytic activity and stereoselectivity for the syndiospecific polymerization of 1 ,3-BD. This activity and selectivity, among other advantages, allows s-PBD to be produced in very high yields within a rubber cement. Additionally, this catalyst composition does not contain CS 2 , and therefore the toxicity, objectionable smell, dangers, and expense associated with the use of CS 2 are eliminated. Further, the Cr-containing and Mo-containing compounds are generally stable, inexpensive, relatively innocuous, and readily available. Furthermore, this catalyst composition has high catalytic activity in a wide variety of solvents including the environmentally preferred non-halogenated solvents such as aliphatic and cycloaliphatic hydrocarbons. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Blends of s-PBD and rubbery elastomers can be directly produced by polymerizing 1 ,3-BD monomer into s-PBD within a rubber cement by using a Cr- based or Mo-based catalyst composition. Blends of s-PBD and rubbery elastomers are produced by (1) providing a mixture of a rubber cement and 1 ,3-BD, where the rubber cement includes at least one rubbery elastomer within an organic solvent and (2) polymerizing the 1 ,3-BD into s-PBD within the rubber cement by using a Cr-based or Mo-based catalyst composition. The Cr-based catalyst composition includes (a) a Cr-containing compound, (b) a hydrogen phosphite, and (c) an org-Mg compound. The Mo-based catalyst composition includes (a) a Mo-containing compound, (b) a hydrogen phosphite, and (c) an org-AI compound. Although a preferred embodiment of the present invention is directed toward the polymerization of 1 ,3-BD into s-PBD within a rubber cement, other conjugated diene monomers can be polymerized to form conjugated diene polymers, preferably crystalline polymers, in a rubber cement. The rubber cement is a solution, preferably viscous, of at least one rubbery elastomer in an organic solvent. Virtually any type of rubbery elastomer can be used to prepare the rubber cement. Some specific examples of suitable rubbery elastomers include, but are not limited to, natural rubber, low-vinyl polybutadiene, c/s-1 ,4-PBD, amorphous 1 ,2-PBD, low-vinyl polyisoprene, c/s-1 ,4-polyisoprene, polyisobutylene, neoprene, ethylene-propylene copolymer rubber (EPR), styrene- butadiene rubber (SBR), styrene-isoprene rubber (SIR), styrene-isoprene-butadiene rubber (SIBR), styrene-butadiene-styrene block copolymer (SBS), styrene-butadiene block copolymer (SB), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), hydrogenated styrene-butadiene block copolymer (SEB), styrene-isoprene- styrene block copolymer (SIS), styrene-isoprene block copolymer (SI), hydrogenated styrene-isoprene-styrene block copolymer (SEPS), hydrogenated styrene-isoprene block copolymer (SEP), polysulfide rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, and the like. Mixtures of the above rubbery elastomers may also be used. These rubbery elastomers are, for the most part, commercially available. Also, these rubbery elastomers can be synthesized readily by using techniques known in the art. The rubber cement can be prepared by dissolving the rubbery elastomer(s) in an organic solvent. When commercially available rubbery elastomers are employed to prepare the rubber cement, it may be necessary to purify the commercial products before use to remove residual water and additives that may become catalyst poisons in the subsequent step of polymerizing 1 ,3-BD into s-PBD within the rubber cement. In a preferred embodiment, the rubber cement is prepared in situ by polymerizing one or more appropriate monomers into rubbery elastomers in an organic solvent within the same reactor subsequently used to polymerize 1 ,3-BD into s-PBD. Many methods of synthesizing the above-mentioned rubbery elastomers are known. Preferably, however, the catalyst utilized in preparing the rubbery elastomers does not contain any ingredients that may interfere with the catalyst subsequently used in the step of polymerizing 1 ,3-BD into s-PBD. Coordination catalyst systems, which are known in the art, can be used for preparing the rubber cement of rubbery elastomers in situ. For example, lanthanide- based catalyst systems comprising a lanthanide compound such as a Nd compound, an alkylating agent, and a source of halogen are described in U.S. Pat. Nos. 3,297,667, 3,541 ,063, and 3,794,604. These lanthanide-based catalyst systems are particularly useful for polymerizing 1 ,3-BD into c/s-1 ,4-PBD rubber. When a coordination catalyst such as the lanthanide-based system is used, the catalyst is preferably inactivated by adding a terminator prior to proceeding with the synthesis of s-PBD within the rubber cement. Suitable terminators include, but are not limited to, alcohols, carboxylic acids, inorganic acids, water, and mixtures thereof. Adding a terminator to inactivate the catalyst system used to synthesize the rubbery elastomers is not always necessary since the catalyst is believed to be inactivated by the hydrogen phosphite component of the Cr-based catalyst composition subsequently used to synthesize the s-PBD. This has been found to be true where a coordination catalyst that includes a Nd compound, an alkylating agent, and a source of halogen ion is used to synthesize the rubbery elastomers. Anionic polymerization initiators, which also are known in the art, can be used to prepare the rubber cement of rubbery elastomers in situ. These initiators include, but are not limited to, organolithium initiators such as butyllithium or functional initiators such as lithium amide initiators, aminoalkyl lithium initiators, and organotin lithium initiators. Exemplary initiators are described in U.S. Pat. Nos. 5,153,159, 5,268,439, 5,274,106, 5,238,893, 5,332,810, 5,329,005, 5,578,542, 5,393,721 , 5,491 ,230, 5,521 ,309, 5,496,940, 5,574,109, 5,523,364, 5,527,753, and 5,550,203. These initiators are particularly useful for synthesizing conjugated diene elastomers or copolymers of conjugated diene and vinyl-substituted aromatic monomers. When an anionic initiator is used, it is preferred to quench the polymerization by adding a terminator prior to proceeding with the synthesis of s-PBD within the rubber cement. Suitable terminators include, but are not limited to, metal halides, organic halides, alcohols, carboxylic acids, inorganic acids, sulfonic acid, water, and mixtures thereof. Metal halides, such as diethylaluminum chloride and ethylaluminum dichloride, are preferred, as are organic halides such as trimethylsilylchloride. Failure to quench the anionic polymerization may interfere with the formation of s-PBD. Other methods for synthesizing rubbery elastomers are known in the art, and the practice of this invention should not be limited to the selection of any particular elastomer, or to any particular method for synthesizing rubbery elastomers. Suitable monomers that can be polymerized to form the rubbery elastomers include conjugated diene monomers. Vinyl-substituted aromatic monomers can be copolymerized with one or more conjugated diene monomers to form rubbery elastomers. Specific examples of suitable conjugated diene monomers that can be polymerized into rubbery elastomers include 1 ,3-BD, 2,3-dimethyl-1 ,3-butadiene, 2- phenyl-1 ,3-butadiene, 2-ethyl-1 ,3-butadiene, isoprene, 1 ,3-pentadiene, 2-methyl-1 ,3- pentadiene, 2,3-dimethyl-1 ,3-pentadiene, 3-methyl-1 ,3-pentadiene, 4-methyl-1 ,3- pentadiene, 1 ,3-hexadiene, 2,4-hexadiene, and 4,5-diethyl-1 ,3-octadiene. Examples of suitable vinyl-substituted aromatic monomers that can be polymerized into rubbery elastomers include one or more of styrene, 4-methylstyrene, α-methylstyrene, 3,5- diethylstyrene, 4-ethylstyrene, 4-propylstyrene, 3,5-diethylstyrene, 2,4,6-trimethyl- styrene, 4-dodecylstyrene, 2,3,4,5-tetraethylstyrene, 3-methyl-5-normal-hexylstyrene, 4-phenylstyrene, 2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 1-vinylnaphthalene, 3- ethyl-1-vinylnaphthalene, 6-isopropyl-1-vinylnaphthalene, 6-cyclohexyl-1-vinylnaph- thalene, 7-dodecyl-2-vinylnaphthalene, and the like. In preparing the rubber cement, use of an organic solvent that is inert with respect to the catalyst systems to be employed to synthesize the rubbery elastomers and the s-PBD generally is preferred. Suitable organic solvents that can be utilized in preparing the rubber cement include, but are not limited to, aliphatic, cycloaliphatic, and aromatic hydrocarbons. Representative examples of suitable aliphatic solvents include n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, isopentane, isohexanes, isoheptanes, isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene, petroleum spirits, and the like. Representative examples of suitable cycloaliphatic solvents include cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, and the like. Representative examples of suitable aromatic solvents include benzene, toluene, xylenes, ethylbenzene, diethyl benzene, mesitylene, and the like. Mixtures of the above hydrocarbons may also be used. For environmental reasons, aliphatic and cycloaliphatic solvents are preferred. The concentration of the rubbery elastomers in the rubber cement varies depending on the types of the rubbery elastomers and organic solvent employed. The concentration of the rubbery elastomers preferably is in a range of from about 5 to about 35% by weight, more preferably from about 10 to 30% by weight, and even more preferably from about 15 to about 25% by weight, of the rubber cement. The foregoing rubber cement is utilized as a polymerization medium for the stereospecific polymerization of 1 ,3-BD into s-PBD. Thus, 1 ,3-BD, a catalyst composition, and optionally additional organic solvent are added to the rubber cement. The order in which the 1 ,3-BD, the catalyst composition, and the solvent are added to the rubber cement does not limit the scope of the invention, although adding the catalyst composition, or at least an ingredient thereof, prior to the addition of 1,3-BD can be preferable in certain circumstances. The amount of 1 ,3-BD added to the rubber cement depends on the proportion of s-PBD desired in the resultant polymer blend. The additional organic solvent can be selected from the organic solvents mentioned above for the preparation of the rubber cement and may be the same as or different from the organic solvent used in preparing the rubber cement. Addition of 1,3-BD to the rubber cement may not be required in the case where 1 ,3-BD is employed to prepare the rubbery elastomers and the polymerization is stopped before all the 1 ,3-BD is consumed. Cr-based catalyst compositions useful for the polymerization of 1,3-BD into s- PBD are described in U.S. Patent Nos. 6,201 ,080 and 6,117,956. A preferred catalyst composition can be formed by combining (a) a Cr-containing compound, (b) a hydrogen phosphite, and (c) an org-Mg compound. Useful Mo-containing catalyst compositions are described in PCT publication WO 00/75201. A preferred catalyst composition can be formed by combining (a) a Mo-containing compound, (b) a hydrogen phosphite, and (c) an org-AI compound. In addition to the three ingredients, other organometallic compounds or Lewis bases also can be added, if desired. Use of Cr-containing or Mo-containing compounds that are soluble in a hydrocarbon solvent such as aromatic hydrocarbons, aliphatic hydrocarbons, or cycloaliphatic hydrocarbons generally is preferred. Hydrocarbon-insoluble Mo- containing or Cr-containing compounds, however, can be suspended in the polymerization medium to form the catalytically active species and are therefore also useful. The metal atom in the Cr-containing and Mo-containing compounds can be in various oxidation states ranging from 0 to +6. (With respect to the Cr-containing compounds, use of chromous compounds or chromic compounds is preferred.) Suitable types of compounds that can be utilized include, but are not limited to, Cr or Mo carboxylates, Cr or Mo organophosphates, Cr or Mo organophosphonates, Cr or Mo organophosphinates, Cr or Mo carbamates, Cr or Mo dithiocarbamates, Cr or Mo xanthates, Cr or Mo β-diketonates, Cr or Mo alkoxides, Cr or Mo aryloxides, Cr or Mo halides, Cr or Mo pseudo-halides, Cr or Mo oxyhalides, and organochromium or organomolybdenum compounds. Some specific examples of suitable compounds of each of the foregoing classes include carboxylates: formate, acetate, acrylate, methacrylate, valerate, gluconate, citrate, fumarate, lactate, maleate, oxalate, 2-ethylhexanoate, neodecanoate, naphthenate, stearate, oleate, benzoate, and picolinate; organophosphates: dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, diheptyl phosphate, dioctyl phosphate, bis(l-methylheptyl) phosphate, bis(2- ethylhexyl) phosphate, didecyl phosphate, didodecyl phosphate, dioctadecyl phosphate, dioleyl phosphate, diphenyl phosphate, bis(p-nonylphenyl) phos- phate, butyl (2-ethylhexyl) phosphate, (1-methylheptyl) (2-ethylhexyl) phosphate, and (2-ethylhexyl) (p-nonylphenyl) phosphate; organophosphonates: butyl phosphonate, pentyl phosphonate, hexyl phosphonate, heptyl phosphonate, octyl phosphonate, (1-methylheptyl) phosphonate, (2- ethylhexyl) phosphonate, decyl phosphonate, dodecyl phosphonate, octadecyl phosphonate, oleyl phosphonate, phenyl phosphonate, (p-nonylphenyl) phosphonate, butyl butylphosphonate, pentyl pentylphosphonate, hexyl hexyl- phosphonate, heptyl heptylphosphonate, octyl octylphosphonate, (1-methylheptyl) (l-methylheptyl)phosphonate, (2-ethylhexyl) (2-ethylhexyl)phosphonate, decyl decylphosphonate, dodecyl dodecylphosphonate, octadecyl octadecyl- phosphonate, oleyl oleylphosphonate, phenyl phenylphosphonate, (p-nonylphenyl) (p-nonylphenyl)phosphonate, butyl (2-ethylhexyl)phosphonate, (2-ethyl- hexyl) butylphosphonate, (1-methylheptyl) (2-ethylhexyl)phosphonate, (2-ethylhexyl) (l-methylheptyl)phosphonate, (2-ethylhexyl) (p-nonylphenyl)phosphonate, and (p-nonylphenyl) (2-ethylhexyl)phosphonate; organophosphinates: butylphosphinate, pentylphosphinate, hexylphosphinate, heptylphosphinate, octylphosphinate, (l-methylheptyl)phosphinate, (2-ethyl- hexyl)phosphinate, decylphosphinate, dodecylphosphinate, octadecyl phos- phinate, oleylphosphinate, phenylphosphinate, (p-nonylphenyl)phosphinate, dibutylphosphinate, dipentylphosphinate, dihexylphosphinate, diheptylphosphi- nate, dioctylphosphinate, bis(1-methylheptyl)phosphinate, bis(2-ethylhexyl)- phosphinate, didecylphosphinate, didodecylphosphinate, dioctadecylphosphi- nate, dioleylphosphinate, diphenylphosphinate, bis(p-nonylphenyl)phosphinate, butyl(2-ethylhexyl)phosphinate, (1 -methylheptyl)(2-ethylhexyl)phosphinate, and (2-ethylhexyl)(p-nonylphenyl)phosphinate; carbamates: dimethylcarbamate, diethylcarbamate, diisopropylcarbamate, dibutylcarbamate, and dibenzylcarbamate; dithiocarbamates: dimethyldithiocarbamate, diethyldithiocarbamate, diisopropyl- dithiocarbamate, dibutyldithiocarbamate, and dibenzyldithiocarbamate; xanthates: methylxanthate, ethylxanthate, isopropylxanthate, butylxanthate, and benzylxanthate; β-diketonates: acetylacetonate, trifluoroacetylacetonate, hexafluoroacetyl- acetonate, benzoylacetonate, 2,2,6,6-tetramethyl-3,5-heptanedionate, dioxide bis(acetylacetonate), dioxide bis(trifluoroacetylacetonate), dioxide bis(hexafluoroacetylacetonate), dioxide bis(benzoylacetonate), and dioxide bis(2,2,6,6-tetramethyl-3,5-heptanedionate); alkoxides or aryloxides: methoxide, ethoxide, isopropoxide, 2-ethylhexoxide, phenoxide, nonylphenoxide, and naphthoxide; halides: hexafluoride, pentafluoride, tetrafluoride, trifluoride, pentachloride, tetra- chloride, trichloride, tetrabromide, tribromide, triiodide, and diiodide; pseudo-halides: cyanide, cyanate, thiocyanate, and azide; and oxyhalides: oxytetrafluoride, dioxydifluoride, oxytetrachloride, oxytrichloride, dioxydichloride, oxytribromide, and dioxydibromide. The term "organochromium compound" refers to any Cr compound containing at least one Cr-C bond. Specific examples of suitable organochromium compounds include tris(allyl)chromium, tris(methallyl)chromium, tris(crotyl)chromium, bis(cyclopentadienyl)chromium, bis(pentamethylcyclopentadienyl)chromium, bis(ethylbenzene)chromium, bis(benzene)chromium, bis(ethylbenzene)chromium, bis(mesitylene)chromium, bis(pentadienyl)chromium, bis(2,4-dimethylpentadienyl)- chromium, bis(allyl)tricarbonylchromium, (cyclopentadienyl)(pentadienyl)chromium, tetra(1-norbornyl)chromium (trimethylenemethane)tetracarbonylchromium, bis(butadiene)dicarbonylchromium, (butadiene)tetracarbonylchromium, and bis(cyclo- octatetraene)chromium. The term "organomolybdenum compound" refers to any Mo compound containing at least one Mo-C bond. Specific examples of suitable organomolybdenum compounds include tris(allyl)molybdenum, tris(methallyl)molybdenum, tris(crotyl)molybdenum, bis(cyclopentadienyl)molybdenum, bis(pentamethylcyclo- pentadienyl)molybdenum, bis(ethylbenzene)molybdenum, bis(mesitylene)molyb- denum, bis(pentadienly)molybdenum, bis(2,4-dimethylpentadienyl)molybdenum, bis(allyl)tricarbonylmolybdenum, (cyclopentadienyl)(pentadienyl)molybdenum, tetra(1 - norbornyl)molybdenum (trimethylenemethane)tetracarbonylmolybdenum, bis(buta- diene)dicarbonylmolybdenum, (butadiene)tetracarbonylmolybdenum, and bis(cyclooctatetraene)molybdenum. Useful hydrogen phosphite compounds that can be employed as ingredient (b) of the catalyst composition can be acyclic and/or cyclic. Acyclic hydrogen phosphites may be represented by the following keto-enol tautomeric structures: where R 1 and R 2 independently are monovalent organic groups. Preferably, R 1 and R 2 are hydrocarbyl groups such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, and alkynyl groups, with each group preferably containing from 1 C atom, or the appropriate minimum number of C atoms to form the group, up to 20 C atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. Acyclic hydrogen phosphites exist mainly as the keto tautomer. The equilibrium constant for the tautomeric equilibrium depends on factors such as temperature, types of R 1 and R 2 groups, type of solvent, and the like. Both tautomers may be associated in dimeric, trimeric or oligomeric forms by hydrogen bonding. Either or both of the two tautomers can be employed as the ingredient (b) of the catalyst composition. Representative, non-limiting examples of suitable acyclic hydrogen phosphites include dimethyl hydrogen phosphite, diethyl hydrogen phosphite, dibutyl hydrogen phosphite, dihexyl hydrogen phosphite, dioctyl hydrogen phosphite, didecyl hydrogen phosphite, didodecyl hydrogen phosphite, dioctadecyl hydrogen phosphite, bis(2,2,2-trifluoroethyl) hydrogen phosphite, diisopropyl hydrogen phosphite, bis(3,3- dimethyl-2-butyl) hydrogen phosphite, bis(2,4-dimethyl-3-pentyl) hydrogen phosphite, di-t-butyl hydrogen phosphite, bis(2-ethylhexyl) hydrogen phosphite, dineopentyl hydrogen phosphite, bis(cyclopropylmethyl) hydrogen phosphite, bis(cyclobutylmethyl) hydrogen phosphite, bis(cyclopentylmethyl) hydrogen phosphite, bis(cyclohexyl- methyl) hydrogen phosphite, dicyclobutyl hydrogen phosphite, dicyclopentyl hydrogen phosphite, dicyclohexyl hydrogen phosphite, dimethyl hydrogen phosphite, diphenyl hydrogen phosphite, dinaphthyl hydrogen phosphite, dibenzyl hydrogen phosphite, bis(l-naphthylmethyl) hydrogen phosphite, diallyl hydrogen phosphite, dimethallyl hydrogen phosphite, dicrotyl hydrogen phosphite, ethyl butyl hydrogen phosphite, methyl hexyl hydrogen phosphite, methyl neopentyl hydrogen phosphite, methyl phenyl hydrogen phosphite, methyl cyclohexyl hydrogen phosphite, methyl benzyl hydrogen phosphite, and the like. Mixtures of the above dihydrocarbyl hydrogen phosphites may also be utilized. Cyclic hydrogen phosphites contain a divalent organic group that bridges between the two oxygen atoms that are singly-bonded to the phosphorus atoms. These cyclic hydrogen phosphites may be represented by the following keto-enol tautomeric structures: where R 3 is a divalent organic group. Preferably, R 3 is a hydrocarbylene group such as, but not limited to, alkylene, cycloalkylene, substituted alkylene, substituted cycloalkylene, alkenylene, cycloalkenylene, substituted alkenylene, substituted cycloalkenylene, arylene, and substituted arylene groups, with each group preferably containing from 1 C atom, or the appropriate minimum number of C atoms to form the group, up to 20 C atoms. These hydrocarbylene groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. Cyclic hydrogen phosphites exist mainly as the keto tautomer. The equilibrium constant for the tautomeric equil- ibrium depends on factors such as temperature, type of R 3 group, type of solvent, and the like. Both tautomers may be associated in dimeric, trimeric or oligomeric forms by hydrogen bonding. Either of the two tautomers or mixtures thereof can be employed as the ingredient (b) of the Cr-based catalyst composition. Cyclic hydrogen phosphites may be synthesized by a transesterification reaction of an acyclic dihydrocarbyl hydrogen phosphite (usually dimethyl hydrogen phosphite or diethyl hydrogen phosphite) with an alkylene or arylene diol. Procedures for this transesterification reaction are well known to those skilled in the art. Typically, transesterification is carried out by heating a mixture of an acyclic dihydrocarbyl hydrogen phosphite and an alkylene or arylene diol. Subsequent distillation of the side product alcohol (usually methanol or ethanol) leaves the newly made cyclic hydrogen phosphite. Examples of suitable cyclic alkylene hydrogen phosphites include 2-oxo-(2H)- 5-butyl-5-ethyl-1 ,3,2-dioxaphosphorinane, 2-oxo-(2H)-5,5-dimethyl-1 ,3,2-dioxaphosphorinane, 2-oxo-(2H)-1 ,3,2-dioxaphosphorinane, 2-oxo-(2H)-4-methyl-1 ,3,2-dioxaphosphorinane, 2-oxo-(2H)-5-ethyl-5-methyl-1 ,3,2-dioxaphosphorinane, 2-oxo-(2H)- 5,5-diethyl-1 ,3,2-dioxaphosphorinane, 2-oxo-(2H)-5-methyl-5-propyl-1 ,3,2-dioxaphosphorinane, 2-oxo-(2H)-4-isopropyl-5,5-dimethyl-1 ,3,2-dioxaphosphorinane, 2-oxo- (2H)-4,6-dimethyl-1 ,3,2-dioxaphosphorinane, 2-oxo-(2H)-4-propyl-5-ethyl-1 ,3,2- dioxaphosphorinane, 2-oxo-(2H)-4-methyl-1 ,3,2-dioxaphospholane, 2-oxo-(2H)-4,5- dimethyl-1 ,3,2-dioxaphospholane, 2-oxo-(2H)-4,4,5,5-tetramethyl-1 ,3,2-dioxaphospholane, and the like. Mixtures of these cyclic alkylene hydrogen phosphites may also be utilized. Examples of suitable cyclic arylene hydrogen phosphites include 2-oxo-(2H)- 4,5-benzo-1 ,3,2-dioxaphospholane, 2-oxo-(2H)-4,5-(3'-methylbenzo)-1 ,3,2-dioxaphospholane, 2-oxo-(2H)-4,5-(4'-methylbenzo)-1 ,3,2-dioxaphospholane, 2-oxo-(2H)-4,5- (4'-tert-butylbenzo)-1 ,3,2-dioxaphospholane, 2-oxo-(2H)-4,5-naphthalo-1 ,3,2-dioxaphospholane, and the like. Mixtures of these cyclic arylene hydrogen phosphites may also be utilized. The Cr-based catalyst composition further includes an org-Mg compound. As used herein, the term "org-Mg compound" refers to any Mg compound containing at least one Mg-C bond. The Mo-based catalyst composition utilized in this invention further includes an org-AI compound. As used herein, the term "org-AI compound" refers to any Al compound containing at least one Al-C bond. Using org-Mg or org-AI compounds that are soluble in a hydrocarbon solvent generally is preferred. A preferred class of org-Mg compounds that can be utilized as ingredient (c) is represented by the general formula MgR 4 2 , where each R 4 independently is a monovalent organic group, with the proviso that the group is attached to the Mg via a C atom. Preferably, each R 4 is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, and alkynyl groups, with each group preferably containing from 1 C atom, or the appropriate minimum number of C atoms to form the group, up to about 20 C atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. Examples of suitable dihydrocarbylmagnesium compounds that can be utilized include diethylmagnesium, di-n-propylmagnesium, diisopropylmagnesium, dibutylmagnesium, dihexylmagnesium, diphenylmagnesium, dibenzylmagnesium, and mixtures thereof. Dibutylmagnesium is particularly useful due to its availability and solubility in aliphatic and cycloaliphatic hydrocarbon solvents. Another class of useful org-Mg compounds is represented by the general formula R 5 MgX where R 5 is a monovalent organic group, with the proviso that the group is attached to the Mg via a C, and X is a hydrogen atom, a halogen atom, a car boxylate group, an alkoxide group, or an aryloxide group. Preferably, R 5 is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, and alkynyl groups, with each group preferably containing from 1 C atom, or the appropriate minimum number of C atoms to form the group, up to about 20 C atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. Preferably, X is a carboxylate group, an alkoxide group, or an aryloxide group, with each group preferably containing 1 to 20 C atoms. Some types of org-Mg compounds represented by the general formula R 5 MgX include, but are not limited, hydrocarbylmagnesium hydride, hydrocarbylmagnesium halide, hydrocarbylmagnesium carboxylate, hydrocarbylmagnesium alkoxide, hydrocarbylmagnesium aryloxide, and mixtures thereof. Examples of suitable org-Mg compounds represented by the general formula R 5 MgX include methylmagnesium hydride, ethylmagnesium hydride, butylmagnesium hydride, hexylmagnesium hydride, phenylmagnesium hydride, benzylmagnesium hydride, methylmagnesium chloride, ethylmagnesium chloride, butylmagnesium chloride, hexylmagnesium chloride, phenylmagnesium chloride, benzylmagnesium chloride, methylmagnesium bromide, ethylmagnesium bromide, butylmagnesium bromide, hexylmagnesium bromide, phenylmagnesium bromide, benzylmagnesium bromide, methylmagnesium hexanoate, ethylmagnesium hexanoate, butylmagnesium hexanoate, hexylmagnesium hexanoate, phenylmagnesium hexanoate, benzylmagnesium hexanoate, methylmagnesium ethoxide, ethylmagnesium ethoxide, butyl- magnesium ethoxide, hexylmagnesium ethoxide, phenylmagnesium ethoxide, benzylmagnesium ethoxide, methylmagnesium phenoxide, ethylmagnesium phenoxide, butylmagnesium phenoxide, hexylmagnesium phenoxide, phenylmagnesium phenoxide, benzylmagnesium phenoxide, and the like, and mixtures thereof. In the Mo-based catalyst composition, a preferred class of org-AI compounds that can be used to form ingredient (c) is represented by the general formula AIRnX3-n where each R independently is a monovalent organic group attached to the Al atom via a C atom, n is an integer of from 1 to 3, and each X independently is a hydrogen atom, halogen atom, carboxylate group, alkoxide group, or aryloxide group. Preferably, each R is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substi- tuted aryl, aralkyl, alkaryl, and alkynyl groups, with each group preferably containing from 1 C atom, or the appropriate minimum number of C atoms to form the group, up to about 20 C atoms. Also, these hydrocarbyl groups may contain heteroatoms such as O, S, N, Si, and P. Preferably, each X is a carboxylate, alkoxide, or aryloxide group, with each group preferably containing from 1 C atom, or the appropriate minimum number of C atoms to form the group, up to about 20 C atoms. Some types of org-AI compounds that can be utilized include, but are not limited to, trihydrocarbylaluminum, dihydrocarbylaluminum hydride, hydrocarbyl- aluminum dihydride, hydrocarbylaluminum dihalide, dihydrocarbylaluminum halide, dihydrocarbylaluminum carboxylate, hydrocarbylaluminum bis(carboxylate), dihydro- carbylaluminum alkoxide, hydrocarbylaluminum dialkoxide, dihydrocarbylaluminum aryloxide, hydrocarbylaluminum diaryloxide, and the like, and mixtures thereof. Trihydrocarbylaluminum compounds are generally preferred. Examples of useful org-AI compounds include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-propylaluminum, triisopropylaluminum, tri- n-butylaluminum, tri-t-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tricyclohexylaluminum, triphenylaluminum, tri-p-tolylaluminum, tribenzylaluminum, trineopentylaluminum, tris(1 -methylcyclopentyl)aluminum, tris(2,6-dimethylphenyl)- aluminum, diethylphenylaluminum, diethyl-p-tolylaluminum, diethylbenzylaluminum, ethyldiphenylaluminum, ethyldi-p-tolylaluminum, ethyldibenzylaluminum, diethyl- aluminum hydride, di-n-propylaluminum hydride, diisopropylaluminum hydride, di-n- butylaluminum hydride, diisobutylaluminum hydride, di-n-octylaluminum hydride, diphenylaluminum hydride, di-p-tolylaluminum hydride, dibenzylaluminum hydride, phenylethylaluminum hydride, phenyl-n-propylaluminum hydride, phenylisopropyl- aluminum hydride, phenyl-n-butylaluminum hydride, phenylisobutylaluminum hydride, phenyl-n-octylaluminum hydride, p-tolylethylaluminum hydride, p-tolyl-n-propylalumi- num hydride, p-tolylisopropylaluminum hydride, p-tolyl-n-butylaluminum hydride, p- tolylisobutylaluminum hydride, p-tolyl-n-octylaluminum hydride, benzylethylaluminum hydride, benzyl-n-propylaluminum hydride, benzylisopropylaluminum hydride, benzyl- n-butylaluminum hydride, benzylisobutylaluminum hydride, and benzyl-n-octylalumi- num hydride, ethylaluminum dihydride, n-propylaluminum dihydride, isopropylalumi- num dihydride, n-butylaluminum dihydride, isobutylaluminum dihydride, n-octylal- uminum dihydride, dimethylaluminum chloride, diethylaluminum chloride, diisobutyl- aluminum chloride, dimethylaluminum bromide, diethylaluminum bromide, dimethyl- aluminum fluoride, diethylaluminum fluoride, methylaluminum dichloride, ethylaluminum dichloride, isobutylaluminum dichloride, methylaluminum dibromide, ethylaluminum dibromide, methylaluminum difluoride, ethylaluminum difluoride, methylaluminum sesquichloride, ethylaluminum sesquichloride, isobutylaluminum sesquichloride, dimethylaluminum hexanoate, diethylaluminum octoate, diisobutyl- aluminum 2-ethylhexanoate, dimethylaluminum neodecanoate, diethylaluminum stearate, diisobutylaluminum oleate, methylaluminum bis(hexanoate), ethylaluminum bis(octoate), isobutylaluminum bis(2-ethylhexanoate), methylaluminum bis(neodeca- noate), ethylaluminum bis(stearate), isobutylaluminum bis(oleate), dimethylaluminum methoxide, diethylaluminum methoxide, diisobutylaluminum methoxide, dimethylaluminum ethoxide, diethylaluminum ethoxide, diisobutylaluminum ethoxide, dimethylaluminum phenoxide, diethylaluminum phenoxide, diisobutylaluminum phenoxide, methylaluminum dimethoxide, ethylaluminum dimethoxide, isobutylaluminum dimethoxide, methylaluminum diethoxide, ethylaluminum diethoxide, isobutylaluminum diethoxide, methylaluminum diphenoxide, ethylaluminum diphenoxide, isobutylaluminum diphenoxide, tris(fluoromethyl)aluminum, and the like, and mixtures thereof. Another class of org-AI compounds that can be utilized to form ingredient (c) of the catalyst composition is aluminoxanes. Aluminoxanes are known in the art and include oligomeric linear aluminoxanes represented by the general formula and oligomeric cyclic aluminoxanes represented by the general formula where x is an integer of from 1 to about 100, preferably about 10 to about 50; y is an integer of from 2 to about 100, preferably about 3 to about 20; and each R 4 independently is a monovalent organic group attached to the Al atom via a C atom. Preferably, each R 4 is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, and alkynyl groups, with each group preferably containing from 1 C atoms, or the appropriate minimum number of C atoms to form the group, up to about 20 C atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. (The number of moles of the aluminoxane refers to the number of moles of the Al atoms rather than the number of moles of the oligomeric aluminoxane molecules. This convention is commonly employed in the art of catalysis utilizing aluminoxanes.) Aluminoxanes can be prepared by reacting trihydrocarbylaluminum compounds with water. This reaction can be performed according to known methods such as (1) a method in which the trihydrocarbylaluminum compound is dissolved in an organic solvent and then contacted with water, (2) a method in which the trihydrocarbylaluminum compound is reacted with water of crystallization contained in, for example, metal salts or water adsorbed in inorganic or organic compounds, and (3) a method in which the trihydrocarbylaluminum compound is added to the monomer or monomer solution to be polymerized, and then water is added. Examples of suitable aluminoxane compounds include methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane, n-propylalumin- oxane, isopropylaluminoxane, n-butylaluminoxane, n-hexylaluminoxane, n-octyl- aluminoxane, isobutylaluminoxane, t-butylaluminoxane, neopentylaluminoxane, cyclohexylaluminoxane, 1-methylcyclopentylaluminoxane, 2,6-dimethylphenyl- aluminoxane, and the like, and mixtures thereof. Isobutylaluminoxane is particularly useful on the grounds of its availability and its solubility in aliphatic and cycloaliphatic hydrocarbon solvents. MMAO can be formed by substituting about 20-80% of the methyl groups of MAO with C 2 -C 12 hydrocarbyl groups, preferably with isobutyl groups, by using techniques known to those skilled in the art. The catalyst composition has very high catalytic activity for polymerizing 1 ,3- BD into s-PBD over a wide range of total catalyst concentrations and catalyst ingredient ratios. The polymers having the most desirable properties, however, are obtained within a narrower range of total catalyst concentrations and catalyst ingredient ratios. Further, the three catalyst ingredients (a), (b), and (c) are believed to interact to form an active catalyst species. Accordingly, the optimum concentration for any one catalyst ingredient depends on the concentrations of the other catalyst ingredients. For example, the molar ratio of hydrogen phosphite to the Cr-containing compound (P/Cr) or to the Mo-containing compound (P/Mo) can be varied from about 0.5:1 to about 50:1 , more preferably from about 1:1 to about 25:1 , and even more preferably from about 2:1 to about 10:1 ; the molar ratio of org-Mg compound to the Cr-containing compound (Mg/Cr) can be varied from about 1 :1 to about 50:1 , more preferably from about 2:1 to about 30:1 , and even more preferably from about 3:1 to about 20:1 ; where ingredient (c) of the Mo-containing catalyst composition includes an org-AI compound defined by the formula AIR^.,,, the molar ratio of the org-AI compound to the Mo-containing compound (Al/Mo) can be varied from about 1:1 to about 100:1, more preferably from about 3:1 to about 50:1 , and even more preferably from about 5:1 to about 25:1 ; and where ingredient (c) of the Mo-containing catalyst composition includes an aluminoxane, the molar ratio of aluminoxane to the Mo-containing compound (Al/Mo) can be varied from about 5:1 to about 500:1 , more preferably from about 10:1 to about 200:1 , and even more preferably from about 20:1 to about 100:1. As discussed above, the catalyst composition preferably is formed by combining ingredients (a), (b), and (c). Although an active catalyst species is believed to result from this combination, the degree of interaction or reaction between the various ingredients or components is not known with a great degree of certainty. Therefore, the term "catalyst composition" has been employed to encompass a simple mixture of the ingredients, a complex of the various ingredients that is caused by physical or chemical forces of attraction, a chemical reaction product of the ingredients, or a combination of the foregoing. The catalyst composition can be formed by combining or mixing the catalyst ingredients or components by using, for example, one of the following methods: 1) The catalyst composition may be formed in situ by adding the three catalyst ingredients to the rubber cement containing the rubbery elastomer and 1 ,3-BD in either a stepwise or simultaneous manner. When adding the catalyst ingredients in a stepwise manner, the addition sequence is not critical. In the Cr- based catalyst system, the org-Mg compound preferably is added first, followed by the Cr-containing compound, and then the hydrogen phosphite; in the Mo- based catalyst system, the Mo-containing compound preferably is added first, followed by the hydrogen phosphite, and then by the org-AI compound. 2) The three catalyst ingredients may be pre-mixed outside the polymerization system at an appropriate temperature, generally from about -20° to about 80°C, and the resulting catalyst composition added to the rubber cement containing the rubbery elastomer and 1 ,3-BD. 3) The catalyst composition may be pre-formed in the presence of 1 ,3- BD. That is, the three catalyst ingredients are pre-mixed in the presence of a small amount of 1,3-BD at an appropriate temperature, generally from about -20° to about 80°C. The amount of 1 ,3-BD used for the catalyst pre-forming can range from about 1 to about 500 moles, more preferably from about 4 to about 100 moles, and even more preferably from about 10 to about 50 moles, per mole of the Mo-containing or Cr-containing compound. The resulting catalyst composition is then added to the rubber cement containing the rubbery elastomer and the remainder of the 1,3-BD to be polymerized. 4) The catalyst composition can also be formed by using a two-stage procedure. The first stage involves combining the Mo-containing or Cr-containing compound and the org-AI or org-Mg compound, respectively, in the presence of a small amount of 1 ,3-BD at an appropriate temperature, generally from about -20° to about 80°C. In the second stage, the foregoing reaction mixture and the hydrogen phosphite are charged in either a stepwise or simultaneous manner to the rubber cement containing the rubbery elastomer and the remainder of the 1 ,3- BD to be polymerized. 5) In an alternative two-stage procedure, a metal-ligand complex is first formed by pre-combining the Mo-containing or Cr-containing compound and the hydrogen phosphite compound. Once formed, this metal-ligand complex is combined with the org-AI or org-Mg compound (as appropriate) to form the active catalyst species. The metal-ligand complex can be formed separately or in the rubber cement containing the rubbery elastomer and the 1 ,3-BD to be polymerized. This complexation reaction can be conducted at any convenient temperature at normal pressure but, for an increased rate of reaction, room temperature or above is preferred. The time required to form the metal-ligand complex is usually within the range of about 10 minutes to about 2 hours after mixing the Mo- containing or Cr-containing compound with the hydrogen phosphite compound. The temperature and time used for the formation of the metal-ligand complex can depend on several variables including the particular starting materials and solvent employed. Once formed, the metal-ligand complex can be used without isolation from the complexation reaction mixture. If desired, however, the metal-ligand complex may be isolated from the complexation reaction mixture before use. 6) The three catalyst ingredients may be added to the rubber cement prior to or simultaneously with the addition of 1 ,3-BD. When a solution of the catalyst composition or one or more of the catalyst ingredients is prepared outside the polymerization system from the foregoing methods, an organic solvent or carrier is preferably employed. Useful solvents include aromatic hydrocarbons, aliphatic hydrocarbons, and cycloaliphatic hydrocarbons. Non-limiting examples of aromatic hydrocarbon solvents include benzene, toluene, xylenes, ethylbenzene, diethylbenzene, mesitylene, and the like. Non- limiting examples of aliphatic hydrocarbon solvents include n-pentane, n-hexane, n- heptane, n-octane, n-nonane, n-decane, isopentane, isohexanes, isopentanes, isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene, petroleum spirits, and the like. Non-limiting examples of cycloaliphatic hydrocarbon solvents include cyclopen- tane, cyclohexane, methylcyclopentane, methylcyclohexane, and the like. Mixtures of the above hydrocarbons may also be used. For environmental reasons, aliphatic and cycloaliphatic solvents are preferred. The foregoing organic solvents may serve to dissolve the catalyst composition or ingredients, or the solvent may simply serve as a carrier in which the catalyst composition or ingredients may be suspended. Production of blends of s-PBD and rubbery elastomers is accomplished by polymerizing 1 ,3-BD within the rubber cement by using a catalytically effective amount of the foregoing catalyst composition. The total catalyst concentration to be employed in the polymerization mass depends on the interplay of various factors such as the purity of the ingredients, polymerization temperature, polymerization rate and conversion desired, and many other factors. Accordingly, a specific total catalyst concentration cannot be definitively set forth except to say that catalytically effective amounts of the respective catalyst ingredients should be used. Generally, the amount of the Mo-containing or Cr-containing compound used can be varied from about 0.01 to about 2 mmol per 100 g 1 ,3-BD, more preferably from about 0.02 to about 1.0 mmol per 100 g 1 ,3-BD, and even more preferably from about 0.05 to about 0.5 mmol per 100 g 1 ,3-BD. In performing the polymerization of 1 ,3-BD into s-PBD within the rubber cement, a molecular weight regulator may be employed to control the molecular weight of the s-PBD to be produced. As a result, the scope of the polymerization system can be expanded so that it can be used to produce s-PBD having a wide range of molecular weights. Suitable types of molecular weight regulators that can be utilized include, but are not limited to, α-olefins such as ethylene, propylene, 1- butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene; accumulated diolefins such as allene and 1 ,2-butadiene; non-conjugated diolefins such as 1 ,6-octadiene, 5- methyl-1 ,4-hexadiene, 1 ,5-cyclooctadiene, 3,7-dimethyl-1 ,6-octadiene, 1,4-cyclo- hexadiene, 4-vinylcyclohexene, 1 ,4-pentadiene, 1 ,4-hexadiene, 1 ,5-hexadiene, 1 ,6- heptadiene, 1 ,2-divinylcyclohexane, 5-ethylidene-2-norbornene, 5-methylene-2- norbomene, 5-vinyl-2-norbornene, dicyclopentadiene, and 1 ,2,4-trivinylcyclohexane; acetylenes such as acetylene, methylacetylene and vinylacetylene; and mixtures thereof. The amount of the molecular weight regulator used, expressed in parts per hundred parts by weight of the 1 ,3-BD monomer (phm), is from about 0.01 to about 10 phm, more preferably from about 0.02 to about 2 phm, and even more preferably from about 0.05 to about 1 phm. The molecular weight of the s-PBD can also be effectively controlled by conducting the polymerization of 1 ,3-BD in the presence of H 2 . In this case, the partial pressure of H 2 is preferably from about 0.01 to about 50 atm. Polymerization of 1,3-BD into s-PBD within the rubber cement may be carried out as a batch process, a continuous process, or even a semi-continuous process. In the semi-continuous process, 1 ,3-BD is intermittently charged as needed to replace that monomer already polymerized. In any case, the polymerization is desirably conducted under anaerobic conditions by using an inert protective gas such as N 2 , Ar or He, with moderate to vigorous agitation. Heat generated by polymerization temperature may vary widely from a low temperature, such as -10°C or below, to a high temperature such as 100°C or above, with a preferred temperature range being from about 20° to about 90°C. Heat generated by polymerization may be removed by external cooling, cooling by evaporation of the 1 ,3-BD or the solvent, or a combination of the two methods. Although the polymerization pressure employed may vary widely, a preferred pressure range is from about 1 to about 10 atm. Once a desired conversion is achieved, the polymerization of 1 ,3-BD within the rubber cement can be stopped by adding a terminator that inactivates the catalyst system. Typically, the terminator is a protic compound which includes, but is not limited to, an alcohol, carboxylic acid, inorganic acid, water, or a combination thereof. An antioxidant such as 2,6-di-teft-butyl-4-methylphenol may be added along with, before or after the addition of the terminator. The amount of antioxidant employed is usually in the range of 0.2 to 1% (by wt.) of the polymer product. When the polymeri- zation reaction has been stopped, the blend of s-PBD and the rubbery elastomer can be recovered from the polymerization mixture by utilizing conventional procedures of desolventizing and drying. For instance, the blend of s-PBD and rubbery elastomer may be isolated from the polymerization mixture by coagulation of the polymerization mixture with an alcohol such as methanol, ethanol, or isopropanol, or by steam distillation of the solvent and the unreacted 1 ,3-BD, followed by filtration. The product is dried to remove residual amounts of solvent and water. The polymer blend produced is a highly dispersed blend of crystalline s-PBD in the rubbery elastomer. Advantageously, the catalyst composition employed in this invention can be manipulated to vary the characteristics of the s-PBD in the polymer blend. Namely, the s-PBD in the polymer blend made by the process of this invention can have various melting temperatures, molecular weights, 1 ,2-linkage contents, and syndio- tacticities, all of which are dependent upon the selection of the catalyst ingredients and the ingredient ratios. Blends of s-PBD and rubbery elastomers have many uses. For example, these blends can be utilized in rubber compositions that are used to manufacture the supporting carcass, innerliner, and tread of tires, in the manufacture of films and packaging materials, and in many molding applications. EXAMPLES Example 1 A highly dispersed blend of s-PBD and low-vinyl PBD was prepared by polymerizing 1 ,3-BD into s-PBD in the presence of a low-vinyl PBD rubber cement. The low-vinyl PBD rubber cement was prepared by charging 449 g hexanes, 911 g 1 ,3-BD/hexanes blend containing 22.4% by weight 1 ,3-BD, and 0.64 mL 1.60 M n-butyllithium in hexanes to a stainless-steel reactor. Polymerization was con- ducted at 65°C for 6 hours. The catalyst was inactivated by the addition of 1.02 mL 1.0 M diethylaluminum chloride. Conversion of the 1 ,3-BD to low-vinyl PBD was determined to be essentially 100% by measuring the weight of the polymer recovered from a small portion of the rubber cement. After the low-vinyl PBD rubber cement was cooled to room temperature, 1048 g hexanes and 2126 g 1 ,3-BD/hexane blend containing 22.4% by weight 1 ,3-BD were added to the rubber cement. Polymerization of the 1 ,3-BD monomer was initiated by adding of 17.5 mL 1.0 M dibutylmagnesium in heptane, 32.7 mL 0.0582 M Cr(lll) 2- ethylhexanoate in hexanes, and 35.8 mL 0.266 M bis(2-ethylhexyl) hydrogen phosphite in hexanes. The polymerization was conducted at 35°C for 4 hours before being stopped by the addition of 3 mL isopropanol diluted with 50 mL hexanes. The polymerization mixture was added into 10 L isopropanol containing 12 g 2,6-di-tert- butyl-4-methylphenol. The blend of s-PBD and low-vinyl PBD was isolated by filtration and dried to a constant weight under vacuum at 60°C. Yield of the polymer blend was 637 g. Conversion of 1 ,3-BD to s-PBD was calculated to be 91 %. As determined by DSC, the polymer blend had a T g of -93°C resulting from the low-vinyl polybutadiene and a melting temperature of 153°C resulting from the s-PBD. Example 2 The procedure of Example 1 was repeated except that the polymerization of the 1 ,3-BD monomer into s-PBD was initiated by adding 21.4 mL 1.0 M dibutylmagnesium in heptane, 40.9 mL 0.0582 M Cr(lll) 2-ethylhexanoate in hexanes, and 61.7 mL 0.193 M of 2-oxo-(2H)-5-butyl-5-ethyl-1,3,2-dioxaphosphorinane in cyclohexane. After work-up of the polymerization mixture, a highly dispersed blend of s- PBD and low-vinyl PBD was obtained. Yield of the polymer blend was 618 g. Conversion of 1 ,3-BD to s-PBD was calculated to be 87%. As determined by DSC, the polymer blend had a T g of -93°C resulting from the low-vinyl PBD and a melting temperature of 141 °C resulting from the s-PBD. Example 3 The procedure of Example 1 was repeated except that the polymerization of the 1 ,3-BD into s-PBD within the low-vinyl PBD rubber cement was initiated by the addition of 15.5 mL 0.215 M molybdenum 2-ethylhexanoate in hexanes, 50.1 mL 0.266 M bis(2-ethyl hexyl) hydrogen phoshpite in hexanes, and 93.1 mL 0.68 M of tri- n-butylaluminum in hexanes. After work-up of the polymerization mixture, a highly dispersed blend of s-PBD and low-vinyl PBD was obtained. Yield of the polymer blend was 618 g. Conversion of 1 ,3-BD to s-PBD was calculated to be 87%. As determined by DSC, the polymer blend had a T g of -93°C resulting from the low-vinyl PBD and a melting temperature of 141 °C resulting from the s-PBD. Example 4 In this experiment, a highly dispersed blend of s-PBD and high cis-1 ,4-PBD was prepared by polymerizing 1 ,3-BD within a high cis-1 ,4-PBD rubber cement. The high cis-1 ,4-PBD rubber cement was prepared by charging 449 g hexanes, 911 g of a 1 ,3-BD/hexanes blend containing 22.4% by weight of 1,3-BD, 9.0 mL 0.68 M triisobutylaluminum in hexanes, 0.41 mL 1.0 M diethylaluminum chloride, and 0.39 mL 0.520 M Nd(lll) neodecanoate in cyclohexane to a stainless steel reactor. The polymerization was carried out at 80°C for 5 hours. Conversion of the 1 ,3-BD to high cis-1 ,4-PBD was determined to be 96% by measuring the weight of the polymer recovered from a small portion of the rubber cement. After the high cis-1 ,4-PBD rubber cement produced above was cooled to room temperature, 1048 g hexanes and 2126 g 1 ,3-BD/hexanes blend containing 22.4% by weight 1 ,3-BD were added to the rubber cement. Example 4a Polymerization of 1 ,3-BD into s-PBD within the rubber cement was initiated by the addition of 17.1 mL 1.0 M dibutylmagnesium in heptane, 32.7 mL 0.0582 M Cr(lll) 2-ethylhexanoate in hexanes, and 35.8 mL 0.266 M bis(2-ethylhexyl) hydrogen phosphite in hexanes. The polymerization was conducted at 35°C for 4 hours. The polymerization was stopped by addition of 3 mL isopropanol diluted with 50 mL hexanes. The polymerization mixture was added into 10 L isopropanol containing 12 g 2,6-di-tert-butyl-4-methylphenol. The resulting blend of s-PBD and high cis-1 ,4- PBD was isolated by filtration and dried to a constant weight under vacuum at 60°C. Yield of the polymer blend was 647 g. Conversion of 1 ,3-BD to s-PBD was calcula- ted to be 93%. As determined by DSC, the polymer blend had a T g of -103°C and a melting temperature of -7°C resulting from the high cis-1 ,4-PBD and a melting temperature of 152°C resulting from the s-PBD. Example 4b Polymerization of 1 ,3-BD into s-PBD within the rubber cement was initiated by addition of 13.3 mL 0.215 M molybdenum 2-ethylhexanoate in hexanes, 43.0 mL 0.266 M bis(2-ethylhexyl) hydrogen phosphite in hexanes, and 63.1 mL 0.68 M triisobutylaluminum in hexanes. The polymerization was conducted at 65°C for 6 hours. The polymerization was stopped by the addition of 3 mL isopropanol diluted with 50 mL hexanes. The polymerization mixture was added into 10 L isopropanol containing 12 g 2,6-di-tert-butyl-4-methylphenol. The resulting blend of s-PBD and high cis-1 ,4-PBD was isolated by filtration and dried to a constant weight under vacuum at 60°C. Yield of the polymer blend was 642 g. Conversion of 1 ,3-BD to s- PBD was calculated to be 92%. As determined by DSC, the polymer blend had a T g of -104°C and a melting temperature of -8°C resulting from the high cis-1 ,4-PBD, and a melting temperature of 185°C resulting from the s-PBD. Example 5a The procedure of Example 4a was repeated except that the polymerization of 1 ,3-BD into s-PBD within the high cis-1 ,4-PBD rubber cement was initiated by adding 21.4 mL 1.0 M dibutylmagnesium in heptane, 40.9 mL 0.0582 M Cr(lll) 2-ethylhexanoate in hexanes, and 61.7 mL 0.193 M 2-oxo-(2H)-5-butyl-5-ethyl-1 ,3,2-dioxaphos- phorinane in cyclohexane. After work-up of the polymerization mixture, a highly dispersed blend of s-PBD and high cis-1 ,4-PBD was obtained. Yield of the polymer blend was 632 g. Conversion of 1 ,3-BD to s-PBD was calculated to be 90%. As determined by DSC, the polymer blend had a T g of -104°C and a melting temperature of -8°C resulting from the high cis-1 ,4-PBD and a melting temperature of 140°C resulting from the s-PBD. Example 5b The procedure of Example 4b was repeated except that the polymerization of 1 ,3-BD into s-PBD within the high cis-1 ,4-PBD rubber cement was initiated by addition of 15.5 mL 0.215 M molybdenum 2-ethylhexanoate in hexanes, 50.1 mL 0.266 M bis(2-ethylhexyl) hydrogen phosphite in hexanes, and 93.1 mL 0.68 M tri-n- butylaluminum in hexanes. After work-up of the polymerization mixture, a highly dispersed blend of s-PBD and high cis-1 ,4-PBD was obtained. Yield of the polymer blend was 628 g. Conversion of 1 ,3-BD to the s-PBD was calculated to be 89%. As determined by DSC, the polymer blend had a T g of -103°C and a melting temperature of -7°C resulting from the high cis-1 ,4-PBD, and a melting temperature of 141°C resulting from s-PBD. In Examples 1-5, after the polymer blend cement was removed from the reactor, visual inspection of the interior of the reactor revealed that the reactor was relatively clean with minimal fouling. Comparative Example 6a In this experiment, polymerization of 1 ,3-BD into s-PBD was conducted in the absence of a rubber cement. A large stainless-steel reactor was charged with 2408 g of hexanes, 2126 g 1 ,3-BD/hexanes blend containing 22.4% by weight 1 ,3-BD, 17.1 mL 1.0 M dibutylmagnesium in heptane, 32.7 mL 0.0582 M Cr(lll) 2-ethylhexanoate in hexanes, and 35.8 mL 0.266 M bis(2-ethylhexyl) hydrogen phosphite in hexanes. The polymeri- zation was conducted at 35°C for 4 hours. The polymerization was stopped by the addition of 3 mL isopropanol diluted with 50 mL hexanes. The polymerization mixture was removed from the reactor and added into 10 L isopropanol containing 12 g 2,6- di-te/ -butyl-4-methylphenol, visual inspection of the interior of the reactor revealed that severe reactor fouling had occurred. In particular, the blades and shafts of the agitator were covered with large chunks of agglomerated polymer particles, and the reactor wall was coated with a thick polymer film. Due to reactor fouling, the reactor had to be opened to recover the remaining polymer inside the reactor. Total yield of s-PBD was 461 g (97%). As determined by DSC, the polymer had a melting temperature of 153°C. Comparative Example 6b In this experiment, polymerization of 1 ,3-BD into s-PBD was conducted in the absence of a rubber cement. A large stainless-steel reactor was charged with 2408 g hexanes, 2126 g 1 ,3- BD/hexanes blend containing 22.4% by weight 1 ,3-butadiene, 11.1 mL 0.215 M molybdenum 2-ethylhexanoate in hexanes, 35.9 mL 0.266 M bis(2-ethylhexyl) hydro- gen phosphite in hexanes, and 52.6 mL 0.68 M triisobutylaluminum in hexanes. The polymerization was conducted at 65°C for 6 hours. The polymerization was stopped by the addition of 3 mL of isopropanol diluted with 50 L hexanes. The polymerization mixture was removed from the reactor and added into 10 L isopropanol containing 12 g 2,6-di-tert-butyl~4-methylphenol, visual inspection of the interior of the reactor revealed that severe reactor fouling had occurred. In particular, the blades and shafts of the agitator were covered with large chunks of agglomerated polymer particles, and the reactor wall was coated with a thick polymer film. Due to reactor fouling, the reactor had to be opened to recover the remaining polymer inside the reactor. Total yield of the s-PBD was 450 g (94%). As determined by DSC, the polymer had a melting temperature of 189°C. Comparative Examples 6a and 6b show that reactor fouling can be a serious problem in the synthesis of s-PBD in the absence of a rubber cement. Examples 1-5 show that by utilizing the process of the present invention, the problem of reactor fouling associated with the synthesis of s-PBD can be greatly reduced.

Claims: CLAIMS I claim: 1. A process for preparing blends of syndiotactic 1 ,2-polybutadiene and rubbery elastomers, the comprising: a) providing a mixture of a rubber cement and 1 ,3-butadiene; and b) polymerizing the 1 ,3-butadiene into syndiotactic 1 ,2-polybutadiene within the rubber cement by using a catalyst composition that is the combination of or the reaction product of ingredients comprising a hydrogen phosphite and either 1) a chromium-containing compound and an organomagnesium compound, or 2) a molybdenum-containing compound and an organoaluminum compound. 2. A blend of syndiotactic 1 ,2-polybutadiene and rubbery elastomers prepared by a process comprising: a) providing a mixture of a rubber cement and 1 ,3-butadiene; and b) polymerizing the 1 ,3-butadiene into syndiotactic 1 ,2-polybutadiene within the rubber cement by using a catalyst composition that is the combination of or the reaction product of ingredients comprising a hydrogen phosphite and either 1) a chromium-containing compound and an organomagnesium compound, or 2) a molybdenum-containing compound and an organoaluminum compound. 3. The process of claim 1 or blend of claim 2, where said providing the mixture of a rubber cement and 1 ,3-butadiene comprises (1) preparing a rubber cement by polymerizing one or more monomers in an organic solvent to form rubbery elastomers, and (2) adding 1 ,3-butadiene to the rubber cement. 4. The process of claim 1 or blend of claim 2, where the rubbery elastomers are natural rubber, low-vinyl polybutadiene, c/s-1 ,4-polybutadiene, amorphous 1 ,2-polybutadiene, low-vinyl polyisoprene, c/s-1 ,4-polyisoprene, polyiso- butylene, neoprene, ethylene-propylene copolymer rubber, styrene-butadiene rubber, styrene-isoprene rubber, styrene-isoprene-butadiene rubber, styrene-butadiene- styrene block copolymer, styrene-butadiene block copolymer, hydrogenated styrene- butadiene-styrene block copolymer, hydrogenated styrene-butadiene block copolymer, styrene-isoprene-styrene block copolymer, styrene-isoprene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, hydrogenated styrene- isoprene block copolymer, polysulfide rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, or mixtures thereof. 5. The process of claim 1 or blend of claim 2, where said step of polymerizing 1 ,3-butadiene into syndiotactic 1 ,2-polybutadiene is conducted in the presence of 0.01 to 2 mmol of the chromium-containing compound or molybdenum- containing compound per 100 g of 1 ,3-butadiene. 6. The process of claim 1 or blend of claim 2, where the hydrogen phosphite is an acyclic hydrogen phosphite defined by the following keto-enol tautomeric structures: or a cyclic hydrogen phosphite defined by the following keto-enol tautomeric structures: or a mixture thereof, where R 1 and R 2 independently are monovalent organic groups and where R 3 is a divalent organic group. 7. The process of claim 1 or blend of claim 2, where the molar ratio of the hydrogen phosphite to the chromium-containing compound or molybdenum- containing compound is from 0.5:1 to 50:1. 8. The process of claim 1 or blend of claim 2, wherein said chromium- containing compound or said molybdenum-containing compound is a carboxylate, organophosphate, organophosphonate, organophosphinate, carbamate, dithio- carbamate, xanthate, β-diketonate, alkoxide, aryloxide, halide, pseudo-halide, oxyhalide, organochromium or organomolybdenum compound, or a mixture thereof. 9. The process of claim 1 or blend of claim 2, wherein the organomagnesium compound is represented by the general formula MgR 4 2 where each R 4 independently is a monovalent organic group or the general formula R 5 MgX, where R 5 is a monovalent organic group, and X is a hydrogen atom, a halogen atom, a carboxylate group, an alkoxide group, or an aryloxide group. 10. The process of claim 1 or blend of claim 2, wherein the organoaluminum compound is represented by the formula AIR n X3- n where each R independently is a monovalent organic group, each X independently is a hydrogen atom, halogenator, carboxylate group, alkoxide group, or aryloxide group, and n is an integer of from 1 to 3 or an aluminoxane represented by one of the following formulas: where x is an integer of 1 to 100, y is an integer of 2 to 100, and each R 4 , independently, is a monovalent organic group.

Inventors: LUO STEVEN, LUO, STEVEN
Applicants: BRIDGESTONE CORP, LUO STEVEN, BRIDGESTONE CORPORATION, LUO, STEVEN
Application year: 2001
Main classification: C08F136
IPC codes: C08F2, C08F4, C08F136, C08F255, C08F279, C08F283, C08F287, C08L9, C08L21, C08L25