WO2001079308A2

WO2001079308A2 - Cr-based catalyst composition for the manufacture of conjugated diene rubber

Info

Publication number: WO2001079308A2
Application number: PCT/US2001/011926
Authority: WO
Inventors: Steven Luo
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 2000-04-13
Filing date: 2001-04-12
Publication date: 2001-10-25
Anticipated expiration: 2002-10-13
Also published as: WO2001079308A3

Abstract

A catalyst composition that is formed by combining a Cr-containing compound, a cyclic hydrogen phosphite, and at least one compound selected from aluminoxanes and compounds defined by the formula AlRnX3-n where each R independently is a monovalent organic group, where each X independently is a halogen atom, a carboxylate group, an alkoxide group, or an aryloxide group, and where n is an integer of from 1 to 3 inclusive. This catalyst composition is useful for polymerizing conjugated diene monomers and is particularly useful for polymerizing 1,3-butadiene into gel-free amorphous high-vinyl polybutadiene.

Description

Cr-BASED CATALYST COMPOSITION FOR THE MANUFACTURE OF CONJUGATED DIENE RUBBER

BACKGROUND OF THE INVENTION

The present invention is directed generally to a catalyst composition for use in polymerizing conjugated dienes into amorphous high-vinyl polymers, more particularly to a Cr-based catalyst composition that is formed by combining a Cr- containing compound, a cyclic hydrogen phosphite, and an organoaluminum compound and that can be used to polymerize 1 ,3-butadiene into gel-free amoφhous high-vinyl polybutadiene (HV-PDB).

Amorphous HV-PDB is a rubbery elastomer that has an atactic structure in which the side chain vinyl groups are located randomly on the opposite sides in relation to the polymeric main chain. Amoφhous HV-PDB is utilized in a variety of applications such as, for example, tire tread compositions because it provides both good traction and low rolling resistance.

Amoφhous HV-PDB is commonly produced by anionic polymerization utilizing alkyllithium initiators modified with Lewis bases such as chelating diamines, ethers, tertiary amines, acetals, ketals, and compounds of similar structures. The vinyl content of PBD prepared by utilizing these Lewis base modifiers decreases drastically as the polymerization temperature is increased; therefore, preparing HV- PDB at high temperatures and using Lewis base modifiers is difficult. Because high polymerization temperatures generally promote a higher polymerization rate, it is often desirable to use moderately high temperatures in commercial polymerizations to maximize productivity as well as reduce production cost.

Japanese patent JP-A-7306939 discloses a process for polymerizing 1 ,3- butadiene into amorphous 1 ,2-PBD by using a catalyst system comprising a soluble Cr(lll) compound, a trialkylaluminum compound, and a dialkyl hydrogen phosphite. The resulting polymer product has an extremely high molecular weight and is partially a gel.

U.S. Pat. No. 4,912,182 discloses a process for synthesizing amoφhous HV- PDB by polymerizing 1 ,3-butadiene in the presence of a catalyst system comprising a Mo-containing compound prepared by modifying MoCI_5l MoCI₃, or MoCI₄ with an alkyl carboxylic acid or an aryl carboxylic acid; and an Al-containing compound prepared by modifying a trialkylaluminum compound with 2-allylphenol. This Mo- based catalyst system has only moderate activity, and polymer yields are about 75%. U.S. Pat. No. 4,751 ,275 discloses a process for polymerizing 1 ,3-butadiene into syndiotactic 1 ,2-PBD by using a catalyst system that includes a hydrocarbon- soluble Cr(lll) compound, a trialkylaluminum compound, and dineopentylphosphite or neopentylmethylphosphite. U.S. Pat. No. 4,148,983 discloses a method for preparing elastomers by polymerizing at least one diolefin selected from trans-1 ,3-pentadiene and isoprene in the presence of a catalyst system comprising a soluble Cr compound, a trialkylaluminum compound, and a dihydrocarbyl hydrogen phosphite. U.S. Pat. Nos. 4,168,357 and 4,168,374 describe a process for polymerizing c/s-1 ,3-pentadiene and trans-l ,3-pentadiene in the presence of the same Cr-based catalyst system.

Because such catalysts known heretofore have many shortcomings, it would be advantageous to develop a new and significantly improved catalyst composition that has high catalytic activity and stereoselectivity for polymerizing conjugated diene monomers, especially 1 ,3-butadiene, into gel-free conjugated diene polymers such as amoφhous HV-PDB.

SUMMARY OF THE INVENTION

The present invention provides a catalyst composition that is the combination of or the reaction product of ingredients comprising (a) a Cr-containing compound, (b) a cyclic hydrogen phosphite, and (c) an organoaluminum compound, where the catalyst composition is essentially devoid of organoaluminum hydride.

The present invention also provides a catalyst composition that is formed by combining ingredients comprising a Cr-containing compound, a cyclic hydrogen phosphite, and at least one compound selected from aluminoxanes and compounds defined by the formula AIRnX3-n where each R, which may be the same or different, is a monovalent organic group, where each X, which may be the same or different, is a halogen atom, a carboxylate group, an alkoxide group, or an aryloxide group, and where n is an integer including 1 , 2, or 3.

The present invention further provides a process for preparing gel-free conjugated diene polymers comprising the step of polymerizing conjugated diene monomers in the presence of a catalytically effective amount of a catalyst composition that is formed by combining (a) a Cr-containing compound, (b) a cyclic hydrogen phosphite, and (c) an organoaluminum compound, where the catalyst composition is essentially devoid of organoaluminum hydride. The present invention further provides a gel-free amorphous HV-PDB that is prepared by a process that includes polymerizing 1 ,3-butadiene monomer with a catalyst composition that is formed by combining (a) a Cr-containing compound, (b) a cyclic hydrogen phosphite, and (c) an organoaluminum compound, where the catalyst composition is essentially devoid of organoaluminum hydride.

Advantageously, the catalyst composition of the present invention has very high catalytic activity and selectivity for polymerizing conjugated diene monomers such as 1 ,3-butadiene. This activity and selectivity, among other advantages, allows amorphous HV-PDB to be produced in very high yields with low catalyst levels after relatively short polymerization times. And, the conjugated diene polymers produced by using the catalyst composition of the present invention are gel-free. Further, this catalyst composition is operational over a wide range of polymerization temperatures. Furthermore, this catalyst composition is Cr-based, and Cr compounds are generally stable, inexpensive, and readily available. Furthermore, the catalyst composition of this invention has high catalytic activity in a wide variety of solvents including the environmentally preferred non-halogenated solvents such as aliphatic and cyclo- aliphatic hydrocarbons.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention is generally directed toward a catalyst composition that is useful for polymerizing conjugated diene monomers into gel-free conjugated diene polymers. It has now been found that conjugated diene monomers can be efficiently polymerized with a Cr-based catalyst composition that is formed by combining a Cr- containing compound, a cyclic hydrogen phosphite, and an organoaluminum (hereinafter "org-AI") compound.

Some specific examples of conjugated dienes that can be polymerized by using the catalyst composition described above include 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, 2,4- hexadiene. Mixtures of two or more conjugated dienes may also be utilized in co- polymerization. The preferred conjugated dienes are 1 ,3-butadiene, isoprene, 1 ,3- pentadiene, and 1 ,3-hexadiene. The most preferred conjugated diene is 1 ,3- butadiene inasmuch as the catalyst composition of this invention advantageously has very high catalytic activity and selectivity for polymerizing 1 ,3-butadiene into gel-free amoφhous high-vinyl polybutadiene. The catalyst composition of the present invention is formed by combining (a) a Cr-containing compound, (b) a cyclic hydrogen phosphite, and (c) an org-AI compound. In addition to the three catalyst ingredients (a), (b), and (c), other organometallic compounds or Lewis bases can also be added, if desired. Various Cr-containing compounds or mixtures thereof can be employed as ingredient (a) of the catalyst composition of this invention. Use of Cr-containing compounds that are soluble in a hydrocarbon solvent such as aromatic hydrocarbons, aliphatic hydrocarbons, or cycloaliphatic hydrocarbons generally is preferred. Hydrocarbon-insoluble Cr-containing compounds, however, can be suspended in the polymerization medium to form the catalytically active species and are therefore also useful.

The chromium atom in the Cr-containing compounds can be in various oxidation states ranging from 0 to +6. Use of divalent Cr compounds (also called chromous compounds), wherein the chromium is in the +2 oxidation state, and trivalent Cr compounds (also called chromic compounds), wherein the Cr is in the +3 oxidation state, is preferred. Suitable types of Cr-containing compounds that can be utilized include, but are not limited to, Cr carboxylates, Cr organophosphates, Cr organophosphonates, Cr organophosphinates, Cr carbamates, Cr dithiocarbamates, Cr xanthates, Cr β-diketonates, Cr alkoxides, Cr aryloxides, Cr halides, Cr pseudo- halides, Cr oxyhalides, and organochromium compounds. Some specific examples of suitable chromium 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) phosphate, butyl (2-ethylhexyl) phosphate, (1-methylheptyl) (2-ethylhexyl) phos- phate, 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-nonyl- phenyl) (p-nonylphenyl)phosphonate, butyl (2-ethylhexyl)phosphonate, (2-ethylhexyl) butylphosphonate, (1-methylheptyl) (2-ethylhexyl)phosphonate, (2-ethylhexyl) (l-methylheptyl)phosphonate, (2-ethylhexyl) (p-nonylphenyl)phospho- nate, and (p-nonylphenyl) (2-ethylhexyl)phosphonate; organophosphinates: butylphosphinate, pentylphosphinate, hexylphosphinate, heptylphosphinate, octylphosphinate, (l-methylheptyl)phosphinate, (2-ethyl- hexyl)phosphinate, decylphosphinate, dodecylphosphinate, octadecylphos- 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: dimethyidithiocarbamate, 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(hexa- fluoroacetylacetonate), 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, tetrachloride, 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 chromium compound containing at least one chromium-carbon bond. Some specific examples of suitable organochromium compounds include tris(allyl)chromium, tris(methallyl)chromium, tris(crotyl)chromium, bis(cyclopentadienyl)chromium, bis(pentamethylcyclopenta- dienyl)chromium, bis(ethylbenzene)chromium, bis(mesitylene)chromium, bis(penta- dienyl)chromium, bis(2,4-dimethylpentadienyl)chromium, bis(allyl)tricarbonyl- chromium, (cyclopentadienyl)(pentadienyl)chromium, tetra(1-norbornyl)chromium (trimethylenemethane)tetracarbonylchromium, bis(cyclooctatetraene)chromium, bis(butadiene)dicarbonylchromium, and (butadiene)tetracarbonylchromium.

Useful cyclic hydrogen phosphite compounds that can be employed as ingredient (b) of the catalyst composition of this invention contain a divalent organic group that bridges between the two oxygen atoms that are singly-bonded to the phosphorus atom. These cyclic hydrogen phosphites may be represented by the following keto-enol tautomeric structures:

where R¹ is a divalent organic group. Preferably, R¹ is a hydrocarbylene group such as, but not limited to, alkylene, cycloalkylene, substituted alkylene, substituted cycloalkylene, alkenylene, cycloalkenylene, substituted alkenylene, substituted cycloalkenylene, arylene, or substituted arylene groups, with each group preferably containing from 1 carbon atom, or the appropriate minimum number of carbon atoms to form the group, up to 20 carbon atoms. These hydrocarbylene groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. The cyclic hydrogen phosphites exist mainly as the keto tautomer (shown on the left), with the enol tautomer (shown on the right) being the minor species. The equilibrium constant for the above-mentioned tautomeric equilibrium is dependent upon factors such as the temperature, the types of R¹ 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. The cyclic hydrogen phosphites may be synthesized by the transesterification reaction of an acyclic dihydrocarbyl hydrogen phosphite (usually dimethyl hydrogen phosphite or diethyl hydrogen phosphite) with an alkylene diol or an arylene diol. Procedures for this transesterification reaction are well known to those skilled in the art. Typically, the transesterification reaction is carried out by heating a mixture of an acyclic dihydrocarbyl hydrogen phosphite and an alkylene diol or an arylene diol. Subsequent distillation of the resulting side product alcohol (usually methanol or ethanol) leaves the newly made cyclic hydrogen phosphite.

Some specific examples of suitable cyclic alkylene hydrogen phosphites are 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-(2HH,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 the above cyclic alkylene hydrogen phosphites may also be utilized. Some specific examples of suitable cyclic arylene hydrogen phosphites are 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'-terf-butylbenzo)-1 ,3,2-dioxaphospholane, 2-oxo-(2H)-4,5-naphthalo- 1 ,3,2-dioxaphospholane, and the like. Mixtures of the above cyclic arylene hydrogen phosphites may also be utilized.

Ingredient (c) of the catalyst composition of the present invention includes an org-AI compound. As used herein, the term "organoaluminum compound" refers to any aluminum compound containing at least one Al-C bond. Use of org-AI compounds that are soluble in a hydrocarbon solvent generally is preferred. A preferred class of org-AI compounds that can be utilized is represented by the general formula AIR_nX₃-_n where each R independently is a monovalent organic group that is attached to the aluminum atom via a carbon atom, n is an integer of from 1 to 3, and each X independently is a halogen atom, a carboxylate group, an alkoxide group, or an aryloxide group. Importantly, both of R and X must not be H atoms because catalyst compositions formed by combining a Cr-containing compound, a hydrogen phosphite, and an org-AI hydride lead to the formation of syndiotactic conjugated diene polymers such as syndiotactic PBD. Preferably, each R is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, or 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 group, an alkoxide group, or an aryloxide group, with each group preferably containing from 1 C atom, or the appro- priate minimum number of carbon atoms to form the group, up to about 20 C atoms. Thus, some suitable types of org-AI compounds that can be utilized include, but are not limited to, trihydrocarbylaluminum, hydrocarbylaluminum dihalide, dihydrocarbylaluminum halide, dihydrocarbylaluminum carboxylate, hydrocarbylaluminum bis(carboxylate), dihydrocarbylaluminum alkoxide, hydrocarbyl- aluminum dialkoxide, dihydrocarbylaluminum aryloxide, hydrocarbylaluminum diaryloxide, and the like, and mixtures thereof. Trihydrocarbylaluminum compounds are generally preferred.

Some specific examples of org-AI compounds that can be utilized include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-propylaluminum, tnisopropylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tricyclohexylaluminum, triphenylaluminum, tri-p-tolylaluminum, tribenzylaluminum, diethylphenylaluminum, diethyl-p-tolylaluminum, diethylbenzylaluminum, ethyldi- phenylaluminum, ethyldi-p-tolylaluminum, ethyldibenzylaluminum, dimethylaluminum chloride, diethylaluminum chloride, diisobutylaluminum chloride, dimethylaluminum bromide, diethylaluminum bromide, dimethylaluminum 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, diisobutylaluminum 2-ethylhexanoate, dimethylaluminum neodecanoate, diethylaluminum stearate, diisobutylaluminum oleate, methylaluminum bis(hexanoate), ethylaluminum bis(octoate), isobutylaluminum bis(2-ethyl- hexanoate), methylaluminum bis(neodecanoate), ethylaluminum bis(stearate), isobutylaluminum bis(oleate), dimethylaluminum methoxide, diethylaluminum meth- oxide, 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 diphen- oxide, ethylaluminum diphenoxide, isobutylaluminum diphenoxide, and the like, and mixtures thereof.

Another class of org-AI compounds that can be employed as ingredient (c) of the catalyst composition of this invention is aluminoxanes. Aluminoxanes are well known in the art and comprise oligomeric linear 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 R² which may be the same or different, is a monovalent organic group that is attached to the aluminum atom via a carbon atom. Preferably, each R² is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, or 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.)

In general, 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 that is to be polymerized, and then water is added.

Some specific examples of suitable aluminoxane compounds that can be utilized include methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane, butylaluminoxane, isobutylaluminoxane, 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 methylaluminoxane with C2-C12 hydrocarbyl groups, preferably with isobutyl groups, by using techniques known to those skilled in the art. The catalyst composition of the present invention has a very high catalytic activity for polymerizing conjugated diene monomers into conjugated diene polymers 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, (a), (b), and (c) are believed to interact to form an active catalyst species. Accordingly, the optimum concentration for any one catalyst ingredient is dependent upon the concentrations of the other two catalyst ingredients. The molar ratio of the cyclic hydrogen phosphite to the Cr-containing compound (P/Cr) 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 org-AI compound to the Cr-containing compound (Al/Cr) can be varied from about 1:1 to about 100:1, more preferably from about 2:1 to about 50:1, and even more preferably from about 3:1 to about 20:1.

As stated above, inasmuch as the use of org-AI hydrides should be avoided, the catalyst composition of this invention should be essentially devoid of org-AI hydrides. The term "essentially devoid" means that the catalyst composition should contain less org-AI hydride than an amount that would interfere with the formation of amoφhous high-vinyl polymer. In fact, it is preferred that the catalyst composition of this invention contain less than about 0.3 moles of an org-AI hydride per mole of the Cr-containing compound, more preferably less than about 0.1 moles of an org-AI hydride per mole of the Cr-containing compound, and even more preferably less than about 0.05 moles of an org-AI hydride per mole of the Cr-containing compound. As discussed above, the catalyst composition of the present invention is preferably formed by combining the three catalyst 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 any great degree of certainty. Therefore, it should be understood that 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 of the present invention 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 a solution containing monomer and solvent, or simply bulk monomer, in either a stepwise or simultaneous manner. When adding the catalyst ingredients in a stepwise manner, the sequence in which the ingredients are added is not critical. Preferably, however, the org-AI compound is added first, followed by the Cr-containing compound, and then followed by the cyclic hydrogen phosphite.

2) The three catalyst ingredients may be pre-mixed outside the polymerization system at an appropriate temperature, which is generally from about -20° to about 80°C, and the resulting catalyst composition is then added to the monomer solution.

3) The catalyst composition may be pre-formed in the presence of monomer. That is, the three catalyst ingredients are pre-mixed in the presence of a small amount of monomer at an appropriate temperature, which is generally from about -20° to about 80°C. The amount of monomer that is used for the catalyst pre-forming can range from about 1 to about 500 moles per mole of the Cr-containing compound, more preferably from about 4 to about 100 moles per mole of the Cr-containing compound, and even more preferably from about 10 to about 50 moles per mole of the Cr-containing compound. The resulting catalyst composition is then added to the remainder of the monomer that is to be polymerized. 4) The catalyst composition may be formed by using a two-stage procedure. The first stage involves combining the Cr-containing compound and the org-AI compound in the presence of a small amount of monomer at an appropriate temperature, which is generally from about -20° to about 80°C. In the second stage, the foregoing reaction mixture and the cyclic hydrogen phosphite are charged in either a stepwise or simultaneous manner to the remainder of the monomer that is to be polymerized.

5) In alternative two-stage procedure, a Cr-ligand complex is first formed by pre-combining the Cr-containing compound with the cyclic hydrogen phosphite. Once formed, this Cr-ligand complex is then combined with the org-

AI compound to form the active catalyst species. The Cr-ligand complex can be formed separately or in the presence of the monomer that is to be polymerized. This complexation reaction can be conducted at any convenient temperature at normal pressure, but for an increased rate of reaction, it is preferable to perform this reaction at room temperature or above. The temperature and time used for the formation of the Cr-ligand complex will depend upon several variables including the particular starting materials and the solvent employed. Once formed, the Cr-ligand complex can be used without isolation from the complexation reaction mixture. If desired, however, the Cr-ligand complex may be isolated from the complexation reaction mixture before use.

When a solution of the Cr-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 is preferably employed. Useful solvents include hydrocarbon solvents such as aromatic hydrocarbons, aliphatic hydrocarbons, and cycloaliphatic hydrocarbons. Non-limiting examples of aromatic hydrocarbon solvents include benzene, toluene, xylenes, ethylbenzene, diethyl- benzene, mesitylene, and the like. Non-limiting examples of aliphatic hydrocarbon solvents include n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n- ecane, isopentane, isohexanes, isopentanes, isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene, petroleum spirits, and the like. Non-limiting examples of cycloaliphatic hydrocarbon solvents include cyclopentane, cyclohexane, methylcyclopen- tane, methylcyclohexane, and the like. Commercial mixtures of the above hydrocarbons may also be used. For environmental reasons, aliphatic and cycloaliphatic solvents are highly 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.

The production of conjugated diene polymers, such as amoφhous high-vinyl polybutadiene, according to this invention is accomplished by polymerizing conjugated diene monomers in the presence of a catalytically effective amount of the foregoing catalyst composition. There are available a variety of methods for bringing the ingredients of the catalyst composition into contact with the conjugated diene monomers as described above. To understand what is meant by a catalytically effective amount, it should be understood that the total catalyst concentration to be employed in the polymerization mass depends on the inteφlay of various factors such as the purity of the ingredients, the polymerization temperature, the polymerization 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. Gener- ally, the amount of the Cr-containing compound used can be varied from about 0.01 to about 2 mmol per 100 g conjugated diene monomers, more preferably from about 0.02 to about 1.0 mmol per 100 g conjugated diene monomers, and even more preferably from about 0.05 to about 0.5 mmol per 100 g conjugated diene monomers. The polymerization of conjugated diene monomers according to this invention is preferably carried out in an organic solvent as the diluent. Accordingly, a solution polymerization system may be employed in which both the monomers 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 Cr-based catalyst composition is usually added to the polymerization system. The additional organic solvent may be either the same as or different from the organic solvent contained in the catalyst solutions. It is normally desirable to select an organic solvent that is inert with respect to the catalyst composition employed to catalyze the polymerization. Suitable types of organic solvents that can be utilized as the diluent include, but are not limited to, aliphatic, cycloaliphatic, and aromatic hydrocarbons. Some representative examples of suitable aliphatic solvents include n-pentane, n- hexane, n-heptane, n-octane, n-nonane, n-decane, isopentane, isohexanes, isopen- tanes, isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene, petroleum spirits, and the like. Some representative examples of suitable cycloaliphatic solvents include cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, and the like. Some representative examples of suitable aromatic solvents include benzene, toluene, xylenes, ethylbenzene, diethylbenzene, mesitylene, and the like. Commercial mixtures of the above hydrocarbons may also be used. For environ- mental reasons, aliphatic and cycloaliphatic solvents are highly preferred.

The concentration of conjugated diene monomers to be polymerized is not limited to a special range. Generally, however, it is preferred that the concentration of the monomers present in the polymerization medium at the beginning of the polymerization be 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.

The polymerization of conjugated diene monomers according to this invention may also be carried out by means of bulk polymerization, 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.

In performing the polymerization of conjugated diene monomers, a molecular weight regulator may be employed to control the molecular weight of the polymers to be produced. As a result, the scope of the polymerization system can be expanded in such a manner that it can be used for the production of amoφhous high-vinyl polymers 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; nonconjugated diolefins such as 1 ,6-octadiene, 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-norbomene, 5-vinyl-2-norbomene, 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 amoφhous high-vinyl polymer produced according to the present invention can also be effectively controlled by polymerizing conjugated diene monomers in the presence of hydrogen gas. In this case, the partial pressure of hydrogen gas is preferably from about 0.01 to about 50 atm.

The polymerization of conjugated diene monomers according to this invention may be carried out as a batch process, a continuous process, or even a semi- continuous process. In the semi-continuous process, monomer 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 N₂, Ar or He, with moderate to vigorous agitation. The polymerization temperature employed in the practice of this invention 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. The heat of polymerization may be removed by external cooling, cooling by evaporation of the monomers 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 can be stopped by the addition of a polymerization terminator that inactivates the catalyst. Typically, the terminator employed is a protic compound, which includes, but is not limited to, an alcohol, a carboxylic acid, an inorganic acid, water, or a mixture thereof. An antioxi- dant such as 2,6-di-fert-butyl-4-methylphenol may be added along with, before or after the addition of the terminator. The amount of the antioxidant employed is preferably in the range of 0.2% to 1 % by weight of the polymer product. When the polymerization reaction has been stopped, the polymer can be recovered from the polymerization mixture by conventional procedures of desolventization and 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 is then dried to remove residual amounts of solvent and water. Advantageously, the catalyst composition of this invention can be utilized to produce amoφhous high-vinyl polybutadiene rubber that is gel-free. For purposes of this disclosure, gel-free means that the amoφhous high-vinyl polybutadiene rubber is essentially soluble in a hydrocarbon solvent. Preferably, the gel-free amorphous high-vinyl polybutadiene produced according to this invention is at least 90% by weight soluble in hydrocarbon solvents, more preferably it is at least 95% by weight soluble in hydrocarbon solvents, even more preferably it is at least 98% by weight soluble in hydrocarbon solvents, and even still more preferably it is 99% by weight soluble in hydrocarbon solvents. This solubility in hydrocarbon solvents is measured by using either an aliphatic or aromatic hydrocarbon solvent. The amoφhous high-vinyl polymers produced with the catalyst composition of the present invention have many uses. For example, the amoφhous high-vinyl polybutadiene can be utilized in rubber compositions that are used to manufacture tire treads having the optimum balance of traction, wear, and rolling resistance.

EXAMPLES

Example 1

A cyclic hydrogen phosphite was synthesized by the transesterification reaction of an acyclic dihydrocarbyl hydrogen phosphite with an alkylene diol. 76.3 g

(0.693 mol) dimethyl hydrogen phosphite and 110.0 g (0.687 mol) 2-butyl-2-ethyl-1 ,3- propanediol were mixed in a round-bottom reaction flask which was connected to a distillation head and a receiving flask. The reaction flask was kept under 1 atm Ar and placed in a silicone oil bath maintained at 150°C. The transesterification reaction proceeded as indicated by the distillation of methanol. After about 2 hours at 150°C, the remaining methanol and any unreacted starting materials were removed by vacuum distillation at 135°C and 20 Pa. The remaining crude product was distilled at 160°C and 0.27 Pa, yielding 128.8 g (0.625 mol, 91% yield) of 2-oxo-(2H)-5-butyl-5- ethyl-1 ,3,2-dioxaphosphorinane as a very viscous, colorless liquid. The identity of the product was established by NMR spectroscopy. 1 H NMR data (CDCI3, 25°C, referenced to tetramethylsilane): δ 6.88 (doublet, ¹J_HP = 675 Hz, 1H, H-P), 4.1 (com- plex, 4 H, OCH2), 0.8-1.8 (complex, 14 H, Et and Bu). ¹³P NMR data (CDCI3, 25°C, referenced to external 85% H3PO4): δ 3.88 (doublet of multiplets, J_HP = 670 Hz).

Example 2 An oven-dried 1L 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 nitrogen gas, the bottle was charged with 106 g hexanes and 227 g 1 ,3-butadiene/ hexanes blend containing 22.0% (by weight) 1,3-butadiene. The following catalyst components were added to the bottle in the following order: (1) 0.45 mmol triethylaluminum, (2) 0.050 mmol Cr(lll) 2-ethylhexanoate, and (3) 0.20 mmol 2-oxo- (2H)-5-butyl-5-ethyl-1 ,3,2-dioxaphosphorinane. The bottle was tumbled for 4 hours in a water bath maintained at 50°C. The polymerization was terminated by addition of 10 mL isopropanol containing 1.0 g 2,6-di-fert-butyl-4-methylphenol. The polymerization mixture was coagulated with 3 L isopropanol. The resulting amoφhous high-vinyl polybutadiene was dried to a constant weight under vacuum at 60°C. The yield of the polymer was 46.7 g (93%). As measured by DSC, the polymer had a T_g of -39°C and had no melting temperature. IR spectroscopic analysis of the polymer indicated a 1,2-linkage content of 78.5% and a c/s-1,4- linkage content of 21.5%. M_w, M_n, and polydispersity index (M_w/M_n) were determined by GPC measurements. The polymer was completely soluble in hydrocarbon solvents, indicating that no gel was formed. The monomer charge, the amounts of the catalyst ingredients, and the properties of the resulting amoφhous HV-PBD are summarized in Table I.

Examples 3-4 In Examples 3-4, the procedure described in Example 2 was repeated except that the catalyst ingredient ratio was varied by adjusting the amount of triethyl- aluminum. The monomer charge, the amounts of the catalyst ingredients, and the properties of the amoφhous HV-PBD produced in each example are summarized in Table I. In each example, the amoφhous HV-PBD produced was completely soluble in hydrocarbon solvents, indicating that no gel was formed.

Examples 5-8

In Examples 5-8, a series of polymerization experiments were carried out to evaluate the usefulness of 1 ,2-butadiene as a molecular weight regulator. In these experiments, the procedure of Example 2 was repeated except that various amounts of 1 ,2-butadiene were added to a polymerization bottle containing the monomer solution before addition of the catalyst ingredients.

In each of these examples, the following amounts were used: 106 g hexanes, 223 g 22.0% 1,3-butadiene/hexanes, 0.050 mmol Cr(lll) (2-EHA)₃, 0.20 mmol 2-oxo- (2H)-5-butyl-5-ethyl-1 ,3,2-dioxaphosphorinane, and 0.55 mmol EtsAI. (The molar ratio of Cr:AI:P for each was 1:4:11.)

The monomer charge, the amounts of the catalyst ingredients, and the properties of the amoφhous HV-PBD produced in each example are summarized in Table II.

Table II

Claims

CLAIMSI claim:

1. A catalyst composition that is the combination of or reaction product of ingredients comprising: a) a chromium-containing compound; b) a cyclic hydrogen phosphite; and c) an organoaluminum compound, where the catalyst composition is essentially devoid of organoaluminum hydride.

2. A catalyst composition that is formed by combining ingredients comprising: a) a chromium-containing compound; b) a cyclic hydrogen phosphite; and c) at least one compound selected from the group consisting of aluminoxanes and compounds defined by the formula AIR_nX3-_n where each R independently is a monovalent organic group; each X independently is a halogen atom, a carboxylate group, an alkoxide group, or an aryloxide group; and n is an integer of from 1 to 3.

3. A process for preparing gel-free conjugated diene polymers comprising polymerizing conjugated diene monomers in the presence of a catalytically effective amount of a catalyst composition that is formed by combining a) a chromium-containing compound; b) a cyclic hydrogen phosphite; and c) an organoaluminum compound, where the catalyst composition is essentially devoid of organoaluminum hydride.

4. The catalyst composition of claims 1 and 2, or the process of claim 3, where the chromium-containing compound is a chromium carboxylate, chromium organophosphate, chromium organophosphonate, chromium organophosphinate, chromium carbamate, chromium dithiocarbamate, chromium xanthate, chromium β-diketonate, chromium alkoxide, chromium aryloxide, chromium halide, chromium pseudo-halide, chromium oxyhalide, organochromium compound, or a mixture thereof.

5. The catalyst composition of claims 1 and 2, or the process of claim 3, where the cyclic hydrogen phosphite is defined by the following keto-enol tautomeric structures:

where R¹ is an alkylene, cycloalkylene, substituted alkylene, substituted cycloalkylene, alkenylene, cycloalkenylene, substituted alkenylene, substituted cycloalkenylene, arylene, or substituted arylene group, with each group containing up to 20 carbon atoms.

6. The catalyst composition of claims 1 and 2, or the process of claim 3, where the organoaluminum compound

(1) is defined by the formula AIR_nX3-_n, where each R independently is a monovalent organic group; each X independently is a halogen atom, a carboxylate group, an alkoxide group, or an aryloxide group; and n is an integer of from 1 to 3, or

(2) is an aluminoxane defined 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 R² independently is a monovalent organic group.

7. The catalyst composition or process of claim 6, where each R is an alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, or alkynyl group, with each group containing up to about 20 carbon atoms, each X is a carboxylate group, an alkoxide group, or an aryloxide group, with each group containing up to about 20 carbon atoms, and each R² is an alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, or alkynyl group, with each group containing up to about 20 carbon atoms.

8. The catalyst composition or process of claim 6, where the organoaluminum compound comprises trihydrocarbylaluminum, hydrocarbylaluminum dihalide, dihydrocarbylaluminum halide, dihydrocarbylaluminum carboxylate, hydro- carbylaluminum bis(carboxylate), dihydrocarbylaluminum alkoxide, hydrocarbylaluminum dialkoxide, dihydrocarbylaluminum aryloxide, hydrocarbylaluminum diaryloxide, an aluminoxane, or mixtures thereof.

9. The catalyst composition of claims 1 and 2, or the process of claim 3, where the molar ratio of the organoaluminum compound to the chromium-containing compound is from about 1 :1 to about 100:1 , and the molar ratio of the cyclic hydrogen phosphite to the chromium-containing compound is from about 0.5:1 to about 50:1.

10. The process of claim 3, where the gel-free conjugated diene polymers are amoφhous high-vinyl polybutadiene polymers that are at least 90 weight percent soluble in a hydrocarbon solvent.