IRON-BASED CATALYST COMPOSITION AND PROCESS FOR PRODUCING CONJUGATED DIENE POLYMERS BACKGROUND INFORMATION 1. Field of the Invention The present invention relates generally to a catalyst composition for use in polymerizing conjugated dienes and in particular to an iron- based composition formed by combining an iron-containing compound, a hydrogen phosphite, and an aluminoxane. Advantageously, the iron- based catalyst composition of this invention can be used to polymerize 1, 3-butadiene into syndiotactic 1, 2-polybutadiene.

2. Background of the Invention 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. S-PBD exhibits properties of both plastics and rubber and accordingly has many uses including the manufacture of films, fibers, and various molded articles. It also can be blended into and co-cured with natural or synthetic rubbers.

S-PBD can be made by solution, emulsion, or suspension polymerizations. Generally, S-PBD has a melting point in the range of about 195° to about 215°C. However, for processability considerations, a melting temperature of less than about 195°C is desirable.

Various 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 no practical utility because they have low catalytic activity or poor stereoselectivity and, in some cases, produce low molecular weight polymers or partially crosslinked polymers unsuitable for commercial use.

Two Co-based catalyst systems are known for the preparation of S-PBD on a commercial scale. The first is based on cobalt bis (acetyl- acetonate) ; see U. S. Pat. Nos. 3, 498, 963 and 4, 182, 813. S-PBD produced using this system has very low crystallinity, and the system develops sufficient catalytic activity only when halogenated hydrocarbon solvents, which present toxicity issues, are used as the polymerization medium. The second is based on cobalt tris (acetylacetonate) ; see U. S.

Pat. No. 3, 778, 424. One of its other components is CS2 which, because of its low flash point, obnoxious smell, high volatility, and toxicity, is difficult and dangerous to use. Furthermore, the S-PBD produced with this catalyst system is difficult to process because it has a very high melting temperature, i. e., about 200° to 210°C. Although the melting temperature of the S-PBD can be reduced by employing a catalyst modifier as an additional catalyst component, the presence of such a modifier has adverse effects on the catalyst activity and polymer yields.

Coordination catalyst systems based on Fe compounds, such as the combination of iron (III) acetylacetonate and triethylaluminum, have been known for some time. However, they have shown very low catalytic activity and poor stereoselectivity for the polymerization of conjugated dienes. The product mixture often contains oligomers, low molecular weight liquid polymers, and partially crosslinked polymers. Therefore, the industrial utility of these Fe-based catalyst systems is very limited.

Developing a catalyst composition that has high catalytic activity and stereoselectivity for polymerizing 1, 3-butadiene into S-PBD remains highly desirable.

SUMMARY OF THE INVENTION Briefly, the present invention provides a catalyst composition that is the combination or reaction product of ingredients that include an iron-

containing compound, a hydrogen phosphite, and an aluminoxane. Also provided is a catalyst composition formed by a process in which these ingredients are combined.

In another aspect, the present invention provides a process of preparing conjugated diene polymers. Such dienes are polymerized in the presence of a catalytically effective amount of the just-described catalyst system. A preferred conjugated diene for this process, because of the many uses of the resulting polymers, is 1, 3-butadiene.

Advantageously, the catalyst composition of the present invention has very high catalytic activity and stereoselectivity for polymerizing conjugated diene monomers such as 1, 3-butadiene. This activity and selectivity, among other advantages, allows S-PBD to be produced in very high yields with low catalyst levels after relatively short polymerization times. Significantly, the catalyst composition of this invention is very versatile and capable of producing S-PBD with a wide range of melting temperatures without the need for a catalyst modifier that may have adverse effects on the catalyst activity and polymer yields. In addition, the present catalyst composition does not contain CS2 ; therefore, the toxicity, objectionable smell, dangers, and expense associated with its use are eliminated. Further, the catalyst composition of this invention is iron-based, and Fe compounds generally are stable, inexpensive, relatively innocuous, and readily available. Furthermore, the present 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 Conjugated dienes, particularly 1, 3-butadiene, now have been found to be capable of being efficiently polymerized with an iron-based

catalyst composition including an iron-containing compound, a hydrogen phosphite, and an aluminoxane. In addition to these three components, other organometallic compounds or Lewis bases also can be included.

Various Fe-containing compounds or mixtures thereof can be employed as ingredient (a) of the catalyst composition. Using Fe- containing compounds that are soluble in a hydrocarbon solvent such as aromatic hydrocarbons, aliphatic hydrocarbons, or cycloaliphatic hydrocarbons can be preferred. (Fe-containing compounds that are insoluble in hydrocarbons can be suspended in the polymerization medium to form the catalytically active species, however.) The Fe atom in the Fe-containing compounds can be in various oxidation states including, but not limited to, 0, +2, +3, and +4. Divalent Fe compounds (also called ferrous compounds) and trivalent Fe com- pounds (also called ferric compounds) can be preferred. Suitable types of Fe-containing compounds that can be utilized include, but are not limited to, iron carboxylates such as iron formate, iron acetate, iron (meth) acrylate, iron valerate, iron gluconate, iron citrate, iron fuma- rate, iron lactate, iron maleate, iron oxalate, iron 2-ethylhexanoate, iron neodecanoate, iron naphthenate, iron stearate, iron oleate, iron benzoate, and iron picolinate ; iron (dithio) carbamates such as iron dimethyl (dithio) carbamate, iron diethyl (dithio) carbamate, iron diisopropyl (dithio) carbamate, iron dibutyl (dithio) carbamate, and iron dibenzyl (dithio) carbamate ; iron xanthates such as iron methylxanthate, iron ethylxanthate, iron isopropylxanthate, iron butylxanthate, and iron benzylxanthate ; iron p-diketonates such as iron acetylacetonate, iron trifluoro- acetylacetonate, iron hexafluoroacetylacetonate, iron benzoylaceto- nate, and iron 2, 2, 6, 6-tetramethyl-3, 5-heptanedionate ; and

iron alkoxides or aryloxides such as iron methoxide, iron ethoxide, iron isopropoxide, iron 2-ethylhexoxide, iron phenoxide, iron nonylphenoxide, and iron naphthoxide ; with the understanding that, in each of the foregoing, the iron can be in the +2 or +3 oxidation state. Organoiron compounds (i. e., compounds containing at least one covalent Fe-C bond) also can be utilized. These include, e. g., ferrocene, decamethylferrocene, bis (pentadienyl) iron (lI), bis (2, 4-dimethylpentadienyl) iron (ll), bis (allyl) dicarbonyliron (ll), (cyclo- pentadienyl) (pentadienyl) iron (tu), tetra (1-norbornyl) iron (IV), (trimethyl- enemethane) tricarbonyliron (II), bis (butadiene) carbonyliron (0), butadienetricarbonyliron (0), and bis (cyclooctatetraene) iron (0).

Useful hydrogen phosphite compounds include acyclic hydrogen phosphites, cyclic hydrogen phosphites, and mixtures thereof. Acyclic hydrogen phosphites may be represented by the keto-enol tautomeric structures : where R'and R2, which may be the same or different, are monovalent organic groups and preferably 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 carbon atom (or the appropriate minimum number of carbon atoms to form these groups) up to 20 carbon atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P atoms. Acyclic hydrogen phosphites exist mainly as the keto tautomer with the equilibrium constant depending on factors such as temperature,

the identity of the R'and R2 groups, the 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. 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 (cyclohexylmethyl) hydrogen phosphite, dicyclobutyl hydrogen phosphite, dicyclopentyl hydrogen phosphite, dicyclohexyl hydrogen phosphite, dimethyl hydrogen phosphite, diphenyl hydrogen phosphite, dinaphthyl hydrogen phosphite, dibenzyl hydrogen phosphite, bis (1-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 phos- phite, methyl cyclohexyl hydrogen phosphite, methyl benzyl hydrogen phosphite, and the like. Mixtures of the foregoing also can be utilized.

Cyclic hydrogen phosphites contain a divalent organic group that bridges between the two O atoms that are singly-bonded to the P atom.

Cyclic hydrogen phosphites may be represented by the keto-enol tautomeric structures :

where R3 is a divalent organic group, preferably 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 carbon atom (or the appropriate minimum number of carbon atoms to form these groups) up to 20 carbon atoms. These hydrocarbylene groups may contain hetero- atoms such as, but not limited to, N, O, Si, S, and P atoms. Cyclic hydrogen phosphites exist mainly as the keto tautomer with the equilib- rium constant depending on factors such as temperature, the identity of the R3 group, the 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 used.

Cyclic hydrogen phosphites may be synthesized by the trans- esterification reaction of an acyclic dihydrocarbyl hydrogen phosphite (usually dimethyl hydrogen phosphite or diethyl hydrogen phosphite) with an alkylene-or arylene diol. Typically, this reaction is performed 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) that results from the transesterifi- cation reaction leaves the newly made cyclic hydrogen phosphite.

Specific examples of suitable cyclic alkylene hydrogen phosphites include 2-oxo-(2H)-5-butyl-5-ethyl-1, 3, 2-dioxaphosphori- nane, 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-dioxaphosphori- nane, 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-dioxaphos-

phorinane, 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-dioxaphosphotane, 2-oxo- (2H)-4, 4, 5, 5-tetramethyl-1, 3, 2-dioxa- phospholane, and the like. Mixtures of these also can be utilized.

Specific 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 theses also can be utilized.

Turning now to the third ingredient, aluminoxanes are known in the art and include oligomeric acyclic aluminoxanes that can be represented by the general formula

and oligomeric cyclic aluminoxanes that can be represented by the general formula

where x is an integer of 1 to about 100, preferably about 10 to about 50 ; y is an integer of 2 to about 100, preferably about 3 to about 20 ; and each R4, which may be the same or different, is a monovalent organic group, preferably a hydrocarbyl group such as alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl,

substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, and alkynyl groups, with each group preferably containing from 1 carbon atom (or the appropriate minimum number of C atoms to form these groups) up to about 20 carbon atoms.

These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P atoms.

(The number of moles of the aluminoxane as used in this application refers to the number of moles of the aluminum atoms rather than the number of moles of the oligomeric aluminoxane molecules. This convention is common in the art of catalysis utilizing aluminoxanes.) In general, aluminoxanes can be prepared by reacting trihydrocarbylaluminum (THCA) compounds with water. This reaction can be performed according to a number of known methods such as (1) dissolving the THCA compound in an organic solvent and then contacting it with water, (2) reacting the THCA compound with water of crystallization contained in, for example, metal salts or water adsorbed in inorganic or organic compounds, and (3) adding the THCA compound is to the monomer or monomer solution to be polymerized followed by the addition of water.

Specific examples of suitable aluminoxane compounds that can be utilized as ingredient (c) include methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane, butylaluminoxane, isobutylaluminoxane and mixtures thereof. Isobutylaluminoxane is preferred because of its availability and solubility in aliphatic and cyclo- aliphatic hydrocarbon solvents. (MMAO can be formed by substituting about 20 to 80% of the methyl groups of MAO with C2 to C, 2 hydrocarbyl groups, preferably isobutyl groups, using techniques known in the art.)

The catalyst composition of this invention has a very high catalytic activity over a wide range of total catalyst concentrations and catalyst ingredient ratios. The polymers having the most desirable properties, however, typically 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 or react to form an active catalyst species. Accordingly, the optimum concentration for any one catalyst ingredient depends on the concentrations of the other catalyst ingredients. The molar ratio of the hydrogen phosphite to the Fe-containing compound (P/Fe) 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 the aluminoxane to the Fe-containing compound (Al/Fe) can be varied from about 1 : 1 to about 200 : 1, more preferably from about 5 : 1 to about 100 : 1, and even more preferably from about 10 : 1 to about 50 : 1.

As discussed above, the catalyst composition preferably is formed by combining the three catalyst ingredients. 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 any 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 any combination of the foregoing.

The catalyst composition of the present invention can be formed by combining or mixing the catalyst ingredients or components by using any of a variety of methods. For example :

The catalyst composition may be formed in situ by adding the catalyst ingredients to a solution containing monomer and solvent, or simply bulk monomer, in either a stepwise or simul- taneous manner. (When using a stepwise addition, the sequence in which the ingredients are added is not critical, although the Fe- containing compound preferably is added first, followed by the hydrogen phosphite, and finally followed by the aluminoxane.) The three catalyst ingredients may be pre-mixed outside the polymerization system (generally at a temperature of from about-20° to about 80°C) and the resulting catalyst composition added to the monomer solution.

The catalyst composition may be pre-formed in the presence of monomer, i. e., the three catalyst ingredients pre- mixed in the presence of a small amount of monomer (e. g., about 1 to about 500 moles, preferably from about 4 to about 100 moles, per mole of the Fe-containing compound) at a temperature of from about-20° to about 80°C and the resulting catalyst composition added to the remainder of the monomer to be polymerized.

The catalyst composition may be formed by a two-stage procedure in which the Fe-containing compound is reacted with the aluminoxane in the presence of a small amount of monomer at a temperature of generally from about-20° to about 80°C and this mixture as well as the hydrogen phosphite are charged in either a stepwise or simultaneous manner to the remainder of the monomer to be polymerized.

The catalyst composition also can be formed by combining an Fe-containing compound with hydrogen phosphite to form an Fe-ligand (which can be done separately or in the presence of the

monomer to be polymerized) that is combined with aluminoxane to form the active catalyst species. 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 temperature and time necessary to form the Fe-ligand complex depend on several variables including the particular starting materials and the solvent employed. Once formed, the Fe-ligand complex can be used with or without isolation from the complexation reaction mixture.

When a solution of the Fe-based catalyst composition or one or more of the catalyst ingredients is prepared outside the polymerization system as set forth in the foregoing methods, an organic solvent or carrier preferably is employed. Selecting an organic solvent that is inert with respect to the catalyst composition or ingredients generally is preferred. 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 cyclopentane, cyclo- hexane, methylcyclopentane, methylcyclohexane, and the like. Mixtures of the foregoing also can 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.

As described above, the present catalyst composition exhibits a very high catalytic activity for polymerizing conjugated dienes. Hence, the present invention further provides a process for producing conjugated diene polymers with the catalyst composition. Some specific examples of useful conjugated dienes include one or more of 1, 3- butadiene, isoprene, 1, 3-pentadiene, 1, 3-hexadiene, 2, 3-dimethyl-1, 3- butadiene, 2-ethyl-1, 3-butadiene, 2-methyl-1, 3-pentadiene, 3-methyl- 1, 3-pentadiene, 4-methyl-1, 3-pentadiene, and 2, 4-hexadiene. Preferred conjugated dienes are 1, 3-butadiene, isoprene, 1, 3-pentadiene, and 1, 3-hexadiene. The catalyst composition of this invention exhibits very high catalytic activity and stereoselectivity when used to convert 1, 3- butadiene into S-PBD.

Production of conjugated diene polymers, such as S-PBD, can be accomplished by polymerizing conjugated diene monomers in the presence of a catalytically effective amount of the foregoing catalyst composition. A variety of methods can be used to bring the ingredients of the catalyst composition into contact with conjugated diene monomers.

The total catalyst concentration to be employed in a given polymerization depends on the interplay of various factors such as the purity of the ingredients, the polymerization temperature, the rate and conversion desired, and many other factors. Accordingly, 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 Fe-containing compound used can be varied from about 0. 01 to about 2 mmol, preferably from about 0. 02 to about 1. 0 mmol, and most preferably from about 0. 05 to about 0. 5 mmol, per 100 g of conjugated diene monomers.

Polymerization of conjugated diene monomers can be carried out in an organic solvent as the diluent. Accordingly, a solution polymeri- zation system may be employed in which both the monomer to be polymerized and the polymer formed are soluble in the polymerization medium. Alternatively, a precipitation polymerization system may be employed by choosing a solvent in which the polymer formed is insoluble. In both cases, an amount of the organic solvent in addition to the organic solvent that may be used in preparing the Fe-based catalyst composition usually is added to the polymerization system. The addition organic solvent may be either the same as or different from the organic solvent contained in the catalyst solutions. Selecting an organic solvent that is inert with respect to the catalyst composition employed to catalyze the polymerization can be preferred. Organic solvents that can be utilized as the diluent include aliphatic, cyclo- aliphatic, and aromatic hydrocarbons. Representative examples of suitable aliphatic 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. 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, diethylbenzene, mesitylene, and the like. Mixtures of the above may also be used. For environmental reasons, aliphatic and cycloaliphatic solvents are preferred.

The concentration of conjugated diene monomers to be polymerized is not limited to a special range although the concentration of the monomers present in the polymerization medium at the beginning of the polymerization preferably are in a range of from about 3 to about

80% by weight, more preferably from about 5 to about 50% by weight, and even more preferably from about 10 to about 30% by weight.

Conjugated diene monomers also can be bulk polymerized, which refers to a polymerization environment where no solvents are employed. Bulk polymerization can be conducted either in a condensed liquid phase or in a gas phase.

Regardless of the polymerization technique employed, a molecular weight regulator may be included to control the molecular weight of the resulting conjugated diene polymers. As a result, conjugated diene polymers having a wide range of molecular weights can be producted.

Suitable molecular weight regulators that can be utilized include, but are not limited to, a-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-octa- diene, 5-methyl-1, 4-hexadiene, 1, 5-cyclooctadiene, 3, 7-dimethyl-1, 6- octadiene, 1, 4-cyclohexadiene, 4-vinylcyclohexene, 1, 4-pentadiene, 1, 4- hexadiene, 1, 5-hexadiene, 1, 6-heptadiene, 1, 2-divinylcyclohexane, 5- ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-vinyl-2-norbor- nene, 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 conjugated diene monomers (phm), is from about 0. 01 to about 10 phm, preferably from about 0. 02 to about 2 phm, and more preferably from about 0. 05 to about 1 phm.

The molecular weight of the conjugated diene polymers to be produced can also be effectively controlled by polymerizing conjugated diene monomers in the presence of H2. When used, the partial pressure of H2 preferably is from about 1 to about 5100 kPa.

Polymerization of conjugated diene monomers can be carried out as a batch process, a continuous process, or even a semi-continuous process (where monomer is intermittently charged as needed to replace that monomer already polymerized). Regardless, the polymerization is desirably conducted under anaerobic conditions by using an inert gas such as N2, Ar, or He, with moderate to vigorous agitation. The polymer- ization temperature employed may vary widely from, for example,-10°C or below to 100°C or above, with a preferred temperature range being from about 20° to about 90°C. Heat generated during polymerization may be removed by external cooling, cooling by evaporation of the monomer 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 100 to about 1000 kPa.

Once a desired conversion is achieved, the polymerization can be stopped by addition of a terminator that inactivates the catalyst.

Typically, the terminator is a protic compound such as, for example, one or more of an alcool, a carboxylic acid, an inorganic acid, and water.

An antioxidant such as 2, 6-di-tert-butyl-4-methylphenol may be added along with, before, or after addition of the terminator. The amount of antioxidant employed preferably is from 0. 2 to 1% by weight of the polymer product. When the polymerization has been stopped, polymer can be recovered from the polymerization mixture by conventional procedures of desolventizing and/or drying. For instance, the polymer 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 monomer, followed by filtration. The polymer product then can dried to remove residual amounts of solvent and water.

As noted above, a preferred embodiment of this invention involves a catalyst composition for polymerizing 1, 3-butadiene into S- PBD. Advantageously, the catalyst composition can be manipulated to vary the characteristics of the resulting S-PBD, namely, melting temp- erature, molecular weight, 1, 2-linkage contents, and syndiotacticities, all of which depend on selection of the catalyst ingredients and ingredient ratios. As a general rule, use of acyclic hydrogen phosphites in lieu of cyclic hydrogen phosphites increases the melting temperature, molecular weight, 1, 2-linkage content, and syndiotacticity of the S-PBD.

S-PBD can be blended with various rubbers to improve the properties thereof. For example, it can be incorporated in elastomers to improve their green strength, particularly in tires. The supporting or reinforcing carcass of tires is particularly prone to distortion during tire building and curing procedures, but this distortion can be minimized or prevented by including S-PBD into the rubber compositions from which the supporting carcass is made. In addition, incorporating S-PBD into tire tread compositions can reduce heat build-up and improve the tear and wear characteristics of tires. S-PBD also can be used in manufac- turing of films and packaging materials and many molding applications.

To demonstrate the practice of the present invention, the following examples are provided.

EXAMPLES Examples 1-6 An oven-dried 1 L glass bottle was capped with a self-sealing rubber liner and a perforated metal cap. After the bottle was thoroughly purged with a stream of dry N2, the bottle was charged with 72 g hexanes and 178 g of a 1, 3-butadiene/hexanes blend containing 28. 1% by weight of 1, 3-butadiene. The following catalyst components were

added to the bottle in the following order : iron (III) 2-ethylhexanoate (IEHA) ; bis (2-ethylhexyl) hydrogen phosphite (BEHHP) ; and isobutylaluminoxane (IBAO).

The bottle was tumbled for 6 hours in a water bath maintained at 50°C. The polymerization was terminated by addition of 10 mL of isopropanol containing 1. 0 g 2, 6-di-tert-butyl-4-methylphenol. The polymerization mixture was coagulated with 3 L isopropanol. The resulting S-PBD was isolated by filtration and dried to a constant weight under vacuum at 60°C.

Melting temperatures were measured by DSC. Proton and 13C nuclear magnetic resonance (NMR) analysis was used to measure 1, 2- linkage content and degree of syndiotacticity of the polymer. Gel permeation chromatography (GPC) was used to measure weight average molecular weight (Mw), number average molecular weight (MJ, and polydispersity index (MW/Mn).

The monomer charge, the amounts of the catalyst ingredients, and the properties of the resulting S-PBD are summarized in the following table.

Table I 1 2 3 4 5 IEHA (mmol) 0. 050 0. 050 0. 050 0. 050 0. 050 BEHHP (mmol) 0. 20 0. 20 0. 20 0. 20 0. 20 IBAO (mmol) 1.60 1.55 1.50 1.45 1.40 Fe/P/Al molar ratio1 : 4 : 32 1 : 4 : 31 1 : 4 : 30 1 : 4 : 29 1 : 4 : 28 Yield (%) 92 93 93 95 96 Tmelt (C) 187 187 187 186 186 Mw (x 104) 1. 113 0. 982 0. 975 0. 934 0. 911 M, (x 104) 0. 416 0. 339 0. 301 0. 367 0. 333 MW/Mn 2.7 2.9 3.2 2.5 2.7

Examples 6-10 The procedure described in Example 1 was repeated except that 2-oxo- (2H)-5-butyl-5-ethyl-1, 3, 2-dioxaphosphorinane (OBED) was substituted for BEHHP, and the catalyst ingredient ratio was further varied. The monomer charge, the amounts of the catalyst ingredients, the polymer yields, and the properties of the S-PBD produced in each example are summarized in the following. Proton and 13C NMR analysis of the polymer produced in Example 7 indicated a 1, 2-linkage content of 80% and a syndiotacticity of 81%.

Table II 6 7 8 9 10 IEHA (mmol) 0. 10 0. 10 0. 10 0. 10 0. 10 OBED (mmol) 0. 40 0. 40 0. 40 0. 40 0. 40 IBAO (mmol) 3. 10 3. 20 3. 30 3. 40 3. 50 Fe/P/Al molar ratio 1 : 4 : 31 1 : 4 : 32 1 : 4 : 33 1 : 4 : 34 1 : 4 : 35 Yield (%) 86 94 92 92 93 Tmelt (C) 158 159 158 157 157 Mw (x 104) 0. 723 0. 716 0. 717 0. 690 0. 674 M, (x 104) 0. 277 0. 303 0. 299 0. 288 0. 315 Mw/Mn 2.6 2.4 2.4 2.4 2.1

Various modifications and alterations that do not depart from the scope and spirit of this invention will become apparent to those skilled in the art. This invention is not to be unduly limited to the illustrative embodiments set forth herein.