WO2002066554A1

WO2002066554A1 - Manufacture of blends of syndiotactic 1,2-polybutadiene and rubbery elastomers

Info

Publication number: WO2002066554A1
Application number: PCT/US2002/004886
Authority: WO
Inventors: Steven Luo
Original assignee: Bridgestone Corporation
Priority date: 2001-02-20
Filing date: 2002-02-20
Publication date: 2002-08-29

Abstract

A process for preparing blends of syndiotactic 1,2-polybutadiene and rubbery elastomers comprising the steps of (1) providing a rubber cement that includes at least one rubbery elastomer in an organic solvent, (2) providing a syndiotactic 1,2-polybutadiene cement that includes a solution of syndiotactic 1,2-polybutadiene in an organic solvent, (3) blending the rubber cement with the syndiotactic 1,2-polybutadiene cement, and (4) recovering the blend of syndiotactic 1,2-polybutadiene and the rubbery elastomer from the blended cement.

Description

MANUFACTURE OF BLENDS OF SYNDIOTACTIC 1,2-POLYBUTADIENE AND RUBBERY ELASTOMERS

This application gains priority from U.S. Provisional Application Serial No. 60/270,038, filed on February 20, 2001.

FIELD OF THE INVENTION

The present invention relates to a process for producing blends of syndiotactic 1,2-polybutadiene and rubbery elastomers.

BACKGROUND OF THE INVENTION

Syndiotactic 1,2-polybutadiene is a high-vinyl polybutadiene having a stereoregular structure in which the side-chain vinyl groups are located alternately on opposite sides of the main polymeric chain. Due to its stereoregular structure, syndiotactic 1,2-polybutadiene is a unique crystalline thermoplastic resin that exhibits the properties of both plastics and rubber, and therefore it has many uses. Films, fibers, and various molded articles can be made from syndiotactic 1,2- polybutadiene. Additionally, it can be blended into and co-cured with natural or synthetic rubbers in order to improve their properties. It is well known that the physical properties of rubbery elastomers can be improved by blending crystalline polymers therein. For example, incorporating syndiotactic 1,2-polybutadiene into rubber compositions utilized in tire supporting carcasses greatly improves the composition's green strength. Likewise, incorporating syndiotactic 1,2-polybutadiene into tire tread compositions can reduce the heat build-up and improve the tire's wear characteristics. The green strength of synthetic rubbers such as cis-l,4-polybutadiene can also be improved by incorporating a small amount of syndiotactic 1,2-polybutadiene.

Blends of crystalline polymers and rubbery elastomers are typically prepared by standard mixing techniques. Blends can be prepared by mixing or kneading and heat-treating a crystalline polymer and a rubbery elastomer by utilizing generally known mixing equipment such as a Banbury mixer, Brabender mixer, extruder, kneader, and mill mixer. These high-temperature mixing procedures, however, 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 syndiotactic 1,2- polybutadiene, polymer degradation and crosslinking are particularly severe problems for mixing syndiotactic 1,2-polybutadiene with elastomers at high temperatures.

U.S. Pat. No. 4,379,889 teaches preparing blends of syndiotactic 1,2- polybutadiene by polymerizing 1,3-butadiene into syndiotactic 1,2-polybutadiene within a rubber cement by using a catalyst comprising a cobalt compound, a dialkylaluminum halide, carbon disulfide, and an electron donative compound. And, U.S. Pat. No. 5,283,284 teaches a similar process employing a catalyst comprising a cobalt compound, an organoaluminum compound, and carbon disulfide. These methods, however, are inferior because their catalyst systems suffer from various disadvantages such as toxicity, objectionable smell, and dangers associated with the use of carbon disulfide. In addition, the rubber cement may contain additives such as antioxidants or catalyst ingredients that are used to prepare the rubbery elastomer. Because these additives can act as poisons to the catalyst system that is used to polymerize 1,3-butadiene into syndiotactic 1,2-polybutadiene, high catalyst levels are often required to yield sufficient amounts of syndiotactic 1,2-polybutadiene within the rubber cement.

Therefore, it would be advantageous to develop a new and significantly improved process for producing blends of syndiotactic 1,2-polybutadiene and rubbery elastomers.

SUMMARY OF THE INVENTION

The present invention provides a process for preparing blends of syndiotactic 1,2-polybutadiene and rubbery elastomers comprising the steps of: (1) providing a rubber cement that includes at least one rubbery elastomer in an organic solvent; (2) providing a syndiotactic 1,2-polybutadiene cement that includes a solution of syndiotactic 1,2-polybutaidene in an organic solvent; (3) blending the rubber cement with the syndiotactic 1,2-polybutadiene cement; and (4) recovering the blend of syndiotactic 1,2-polybutadiene and the rubbery elastomer from the blended cement.

The present invention further includes a rubbery elastomer/syndiotactic 1,2-polybutadiene blend prepared by a process comprising the steps of (1) providing a rubber cement that includes at least one rubbery elastomer in an organic solvent, (2) providing a syndiotactic 1,2-polybutadiene cement that includes a solution of syndiotactic 1,2-polybutadiene in an organic solvent, (3) blending the rubber cement with the syndiotactic 1,2-polybutadiene cement, and (4) recovering the blend of syndiotactic 1,2-polybutadiene and the rubbery elastomer from the blended cement. According to the process of the present invention, the rubber cement and the syndiotactic 1,2-polybutadiene cement are prepared separately before blending. Therefore, interference with the catalyst used to produce syndiotactic 1,2-polybutadiene by the additives, such as antioxidants and catalyst residues, in the rubber cement is eliminated. Advantageously, the process of this invention provides blends of syndiotactic 1,2-polybutadiene and rubbery elastomers without the necessity of utilizing a high-temperature mixing step. Also, good dispersion of syndiotactic 1,2-polybutadiene throughout rubbery elastomers can be easily and economically achieved. Significantly, the process of this invention 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.

Further, the preferred use of an iron-based catalyst system to prepare the syndiotactic 1,2-polybutadiene cement offers many advantages. For example, the preferred iron-based catalyst composition has very high catalytic activity for the syndiospecific polymerization of 1,3-butadiene. This activity and selectivity, among other advantages, provides syndiotactic 1,2-polybutadiene in very high yields with low catalyst levels after relatively short polymerization times. Additionally, this catalyst composition does not contain carbon disulfide, and therefore the toxicity, objectionable smell, dangers, and expense associated with the use of carbon disulfide are eliminated. Further, this catalyst composition is iron-based, and iron compounds are generally stable, inexpensive, relatively innocuous, and readily available. Furthermore, this catalyst composition has a high catalytic activity in a wide variety of solvents including the environmentally- preferred nonhalogenated solvents such as aliphatic and cycloaliphatic hydrocarbons, and this catalyst is capable of producing solutions of syndiotactic 1,2-polybutadiene within these solvents.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Blends of syndiotactic 1,2-polybutadiene and rubbery elastomers are prepared by the steps of: (1) providing a rubber cement that includes at least one rubbery elastomer in an organic solvent, (2) providing a syndiotactic 1,2- polybutadiene cement by polymerizing 1,3-butadiene into syndiotactic 1,2- polybutadiene within an organic solvent in the presence of an iron-based catalyst composition that is formed by combining an iron-containing compound, a hydrogen phosphite, and an organoaluminum compound, (3) blending the rubber cement with the syndiotactic 1,2-polybutadiene cement, and (4) recovering the blend of syndiotactic 1,2-polybutadiene and the rubbery elastomer from the blended cement.

The term "rubber cement" refers to a solution of at least one rubbery elastomer in an organic solvent. Virtually any type of rubbery elastomer that is soluble in an organic solvent can be used to prepare the rubber cement. Suitable rubbery elastomers include, but are not limited to, natural rubber, cis-1,4- polybutadiene, amorphous 1,2-polybutadiene, polyisoprene, polyisobutylene, neoprene, ethylene-propylene copolymer rubber (EPR), ethylene-propylene-diene terpolymer rubber (EPDM), 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 mixtures thereof. These rubbery elastomers are well known and, for the most part, are commercially available. Also, those skilled in the art can use well-known techniques in synthesizing these elastomers.

Suitable types of organic solvents include, but are not limited to, aliphatic, cycloaliphatic, and aromatic hydrocarbons. 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. Examples of cycloaliphatic solvents include cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, and the like. Examples of aromatic solvents include benzene, toluene, xylenes, ethylbenzene, diethylbenzene, mesitylene, and the like. Commercial mixtures of the above hydrocarbons may also be used. For environmental reasons, aliphatic and cycloaliphatic solvents are highly preferred.

The rubber cement can be prepared by dissolving the commercially available products of the above-mentioned rubbery elastomers in an organic solvent. Preferably, however, the rubber cement is prepared in situ by polymerizing one or more appropriate monomers in an organic solvent. When the rubber cement is prepared in situ by polymerizing one or more appropriate monomers, it is desirable to select an organic solvent that is inert with respect to the catalyst system being employed. The concentration of the rubbery elastomers in the rubber cement varies depending on the types of the rubbery elastomers and the organic solvent employed. It is generally preferred that the concentration of the rubbery elastomers be in a range of from about 5% to about 35% by weight of the rubber cement, more preferably from about 10% to about 30% by weight of the rubber cement, and even more preferably from about 15% to about 25% by weight of the rubber cement.

Many methods of synthesizing rubbery elastomers are well known in the art. For example, anionic polymerization initiators can be used for preparing the rubber cement 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. These initiators are particularly useful for synthesizing conjugated diene elastomers or copolymers of conjugated diene monomers and vinyl- substituted aromatic monomers.

Transition metal catalysts (also called coordination catalysts) can also be used for preparing the rubber cement in situ. For example, lanthanide-based catalyst systems that comprise a lanthanide compound such as neodymium carboxylate, an organoaluminum compound, and a source of halogen are particularly useful for polymerizing 1,3-butadiene into cis-l,4-polybutadiene rubber.

Other methods that are useful for synthesizing rubbery elastomers in situ are known in the art, and the practice of this invention should not be limited to the selection of any particular rubbery elastomer or to any particular method for synthesizing rubbery elastomers.

When the rubber cement is prepared in situ by polymerizing one or more appropriate monomers in an organic solvent, the catalyst is preferably quenched by adding a terminator prior to blending the rubber cement with the syndiotactic 1,2-polybutadiene cement. Suitable terminators include, but are not limited to, alcohols, carboxylic acids, inorganic acids, water, and mixtures thereof. An antioxidant such as 2,6-di-tert-butyl-4-methylphenol may be added along with, before, or after the addition of the terminator; the amount of the antioxidant is usually in the range of 0.2% to 1% by weight of the rubbery elastomers.

In addition to the antioxidant, a processing oil may be added to the rubber cement along with, before, or after the addition of the terminator. Preferred processing oils include those oils that are typically employed to extend cements of rubbery elastomers. Non-limiting examples include paraffinic, aromatic, and naphthenic oils. Those skilled in the art will be able to determine useful amounts of processing oil without undue experimentation.

The term "syndiotactic 1,2-polybutadiene cement" refers to a solution having a least one syndiotactic 1,2-polybutadiene polymer dissolved in an organic solvent. The concentration of syndiotactic 1,2-polybutadiene (SPB) polymers in the SPB cement is generally preferred to be in a range from about 5% to about 30% by weight of the SPB cement, more preferably from about 10% to about 25% by weight of the SPB cement, and more preferably from about 15% to about 20% by weight of the SPB cement.

The syndiotactic 1,2-polybutadiene cement is preferably prepared by polymerizing 1,3-butadiene in an organic solvent in the presence of an iron-based catalyst composition. An exemplary system is described in U.S. Pat. Nos. 6,180,734, 6,211,313, 6,277,779, and 6,288,183, which are incorporated herein by reference. Generally, the catalyst composition is formed by combining (a) an iron-containing compound, (b) a hydrogen phosphite, and (c) an organoaluminum compound. In addition to the three catalyst ingredients (a), (b), and (c), other organometallic compounds or Lewis bases may be added if desired.

Ingredient (a) of the iron-based catalyst composition may include various iron-containing compounds or mixtures thereof. Iron-containing compounds that are soluble in a hydrocarbon solvent, such as aromatic hydrocarbons, aliphatic hydrocarbons, or cycloaliphatic hydrocarbons are preferably employed. Hydrocarbon-insoluble iron-containing compounds, however, that are suspended in the polymerization medium are also useful.

The iron atom in the iron-containing compounds can be in various oxidation states including but not limited to the 0, +2, +3, and +4 oxidation states. Divalent iron compounds (also called ferrous compounds), wherein the iron atom is in the +2 oxidation state, and trivalent iron compounds (also called ferric compounds), wherein the iron atom is in the +3 oxidation state, are preferred. Suitable iron-containing compounds include, but are not limited to, iron carboxylates, iron organophosphates, iron organophosphonates, iron organophosphinates, iron carbamates, iron dithiocarbamates, iron xanthates, iron α-diketonates, iron alkoxides or aryloxides, and organoiron compounds.

Suitable iron carboxylates include iron(II) formate, iron(III) formate, iron (II) acetate, iron (III) acetate, iron (II) acrylate, iron (III) acrylate, iron(II) methacrylate, iron(III) methacrylate, iron(II) valerate, iron(III) valerate, iron (II) gluconate, iron (III) gluconate, iron (II) citrate, iron (III) citrate, iron (II) fumarate, iron(III) fumarate, iron(II) lactate, iron(III) lactate, iron(II) maleate, iron (III) maleate, iron (II) oxalate, iron (III) oxalate, iron (II) 2-ethylhexanoate, iron(III) 2-ethylhexanoate, iron(II) neodecanoate, iron(III) neodecanoate, iron(II) naphthenate, iron (III) naphthenate, iron (II) stearate, iron (III) stearate, iron (II) oleate, iron(III) oleate, iron(II) benzoate, iron(III) benzoate, iron(II) picolinate, and iron (III) picolinate.

Suitable iron organophosphates include iron (II) dibutyl phosphate, iron(III) dibutyl phosphate, iron(II) dipentyl phosphate, iron(III) dipentyl phosphate, iron (II) dihexyl phosphate, iron (III) dihexyl phosphate, iron (II) diheptyl phosphate, iron (III) diheptyl phosphate, iron (II) dioctyl phosphate, iron(III) dioctyl phosphate, iron(II) bis(l-methylheptyl) phosphate, iron(III) bis(l-methylheptyl) phosphate, iron(II) bis (2-ethylhexyl) phosphate, iron(III) bis (2-ethylhexyl) phosphate, iron(II) didecyl phosphate, iron(III) didecyl phosphate, iron (II) didodecyl phosphate, iron (III) didodecyl phosphate, iron (II) dioctadecyl phosphate, iron (III) dioctadecyl phosphate, iron (II) dioleyl phosphate, iron (III) dioleyl phosphate, iron (II) diphenyl phosphate, iron (III) diphenyl phosphate, iron(II) bis (p -nonylphenyl) phosphate, iron(III) bis(p-nonylphenyl) phosphate, iron(II) butyl (2-ethylhexyl) phosphate, iron(III) butyl (2-ethylhexyl) phosphate, iron(II) (1-methylheptyl) (2-ethylhexyl) phosphate, iron(III) (1- methylheptyi) (2-ethylhexyl) phosphate, iron(II) (2-ethylhexyl) (p-nonylphenyl) phosphate, and iron (III) (2-ethylhexyl) (p-nonylphenyl) phosphate.

Suitable iron organophosphonates include iron(II) butyl phosphonate, iron (III) butyl phosphonate, iron (II) pentyl phosphonate, iron (III) pentyl phosphonate, iron (II) hexyl phosphonate, iron (III) hexyl phosphonate, iron (II) heptyl phosphonate, iron (III) heptyl phosphonate, iron (II) octyl phosphonate, iron (III) octyl phosphonate, iron (II) (1-methylheptyl) phosphonate, iron (III) (1-methylheptyl) phosphonate, iron(II) (2-ethylhexyl) phosphonate, iron(III) (2-ethylhexyl) phosphonate, iron (II) decyl phosphonate, iron (III) decyl phosphonate, iron(II) dodecyl phosphonate, iron(III) dodecyl phosphonate, iron (II) octadecyl phosphonate, iron (III) octadecyl phosphonate, iron (II) oleyl phosphonate, iron(III) oleyl phosphonate, iron(II) phenyl phosphonate, iron(III) phenyl phosphonate, iron(II) (p-nonylphenyl) phosphonate, iron(III) (p- nonylphenyl) phosphonate, iron(II) butyl butylphosphonate, iron(III) butyl butylphosphonate, iron(II) pentyl pentylphosphonate, iron(II) pentyl pentylphosphonate, iron (II) hexyl hexylphosphonate, iron (III) hexyl hexylphosphonate, iron (II) heptyl heptylphosphonate, iron (III) heptyl heptylphosphonate, iron (II) octyl octylphosphonate, iron (III) octyl octylphosphonate, iron(II) (1-methylheptyl) (l-methylheptyl)phosphonate, iron(III) (1-methylheptyl) (1-methylheptyl) phosphonate, iron(II) (2-ethylhexyl) (2-ethylhexyl)phosphonate, iron(III) (2-ethylhexyl) (2-ethylhexyl)phosphonate, iron (II) decyl decylphosphonate, iron (III) decyl decylphosphonate, iron (II) dodecyl dodecylphosphonate, iron (III) dodecyl dodecylphosphonate, iron (II) octadecyl octadecylphosphonate, iron (III) octadecyl octadecylphosphonate, iron (II) oleyl oleylphosphonate, iron (III) oleyl oleylphosphonate, iron (II) phenyl phenylphosphonate, iron (III) phenyl phenylphosphonate, iron (II) (p-nonylphenyl) (p-nonylphenyl) phosphonate, iron (III) (p-nonylphenyl) (p- nonylphenyl) phosphonate, iron(II) butyl (2-ethylhexyl)phosphonate, iron(III) butyl (2-ethylhexyl) phosphonate, iron(II) (2-ethylhexyl) butylphosphonate, iron(III) (2-ethylhexyl) butylphosphonate, iron(II) (1-methylheptyl) (2- ethylhexyl) phosphonate, iron(III) (1-methylheptyl) (2-ethylhexyl)phosphonate, iron(II) (2-ethylhexyl) (1-methylheptyl) phosphonate, iron(III) (2-ethylhexyl) (1- methylheptyl) phosphonate, iron(II) (2-ethylhexyl) (p-nonylphenyl) phosphonate, iron(III) (2-ethylhexyl) (p-nonylphenyl) phosphonate, iron(II) (p-nonylphenyl) (2- ethylhexyl) phosphonate, and iron (III) (p-nonylphenyl) (2- ethylhexyl) phosphonate.

Suitable iron organophosphinates include iron(II) butylphosphinate, iron (III) butylphosphinate, iron (II) pentylphosphinate, iron (III) pentylphosphinate, iron (II) hexylphosphinate, iron (III) hexylphosphinate, iron (II) heptylphosphinate, iron (III) heptylphosphinate, iron (II) octylphosphinate, iron(III) octylphosphinate, iron(II) (l-methylheptyl)phosphinate, iron(III) (l-methylheptyl)phosphinate, iron(II) (2-ethylhexyl) phosphinate, iron(III) (2-ethylhexyl)phosphinate, iron(II) decylphosphinate, iron(III) decylphosphinate, iron (II) dodecylphosphinate, iron (III) dodecylphosphinate, iron (II) octadecylphosphinate, iron (III) octadecylphosphinate, iron (II) oleylphosphinate, iron(III) oleylphosphinate, iron(II) phenylphosphinate, iron(III) phenylphosphinate, iron(II) (p-nonylphenyl) phosphinate, iron(III) (p- nonylphenyl) phosphinate, iron (II) dibutylphosphinate, iron (III) dibutylphosphinate, iron(II) dipentylphosphinate, iron(III) dipentylphosphinate, iron (II) dihexylphosphinate, iron (III) dihexylphosphinate, iron (II) diheptylphosphinate, iron (III) diheptylphosphinate, iron (II) dioctylphosphinate, iron(III) dioctylphosphinate, iron(II) bis (1-methylheptyl) phosphinate, iron(III) bis (1-methylheptyl) phosphinate, iron(II) bis(2-ethylhexyl)phosphinate, iron(III) bis(2-ethylhexyl)phosphinate, iron(II) didecylphosphinate, iron(III) didecylphosphinate, iron (II) didodecylphosphinate, iron (III) didodecylphosphinate, iron (II) dioctadecylphosphinate, iron (III) dioctadecylphosphinate, iron (II) dioleylphosphinate, iron (III) dioleylphosphinate, iron (II) diphenylphosphinate, iron (III) diphenylphosphinate, iron (II) bis(p- nonylphenyl) phosphinate, iron (III) bis (p-nonylphenyl) phosphinate, iron (II) butyl(2-ethylhexyl)phosphinate, iron(III) butyl(2-ethylhexyl)phosphinate, iron(II) (1-methylheptyl) (2-ethylhexyl)phosphinate, iron(III) (1-methylheptyl) (2- ethylhexyl) phosphinate, iron(II) (2-ethylhexyl) (p-nonylphenyl) phosphinate, and iron(III) (2-ethylhexyl) (p-nonylphenyl) phosphinate.

Suitable iron carbamates include iron (II) dimethylcarbamate, iron (III) dimethylcarbamate, iron (II) diethylcarbamate, iron (III) diethylcarbamate, iron (II) diisopropylcarbamate, iron (III) diisopropylcarbamate, iron (II) dibutylcarbamate, iron (III) dibutylcarbamate, iron (II) dibenzylcarbamate, and iron(III) dibenzylcarbamate.

Suitable iron dithiocarbamates include iron (II) dimethyldithiocarbamate, iron (III) dimethyldithiocarbamate, iron (II) diethyldithiocarbamate, iron (III) diethyldithiocarbamate, iron (II) diisopropyldithiocarbamate, iron (III) diisopropyldithiocarbamate, iron (II) dibutyldithiocarbamate, iron(III) dibutyldithiocarbamate, iron(II) dibenzyldithiocarbamate, and iron(III) dibenzyldithiocarbamate. Suitable iron xanthates include iron(II) methylxanthate, iron(III) methylxanthate, iron (II) ethylxanthate, iron (III) ethylxanthate, iron (II) isopropylxanthate, iron (III) isopropylxanthate, iron (II) butylxanthate, iron (III) butylxanthate, iron (II) benzylxanthate, and iron(III) benzylxanthate.

Suitable iron α-diketonates include iron(II) acetylacetonate, iron(III) acetylacetonate, iron (II) trifluoroacetylacetonate, iron (III) trifluoroacetylacetonate, iron (II) hexafluoroacetylacetonate, iron (III) hexafluoroacetylacetonate, iron (II) benzoylacetonate, iron (III) benzoylacetonate, iron(II) 2,2,6,6-tetramethyl-3,5-heptanedionate, and iron(III) 2,2,6,6-tetramethyl- 3 , 5-heptanedionate . Suitable iron alkoxides or aryloxides include iron (II) methoxide, iron (III) methoxide, iron (II) ethoxide, iron (III) ethoxide, iron (II) isopropoxide, iron(III) isopropoxide, iron(II) 2-ethylhexoxide, iron(III) 2-ethylhexoxide, iron(II) phenoxide, iron (III) phenoxide, iron (II) nonylphenoxide, iron (III) nonylphenoxide, iron (II) naphthoxide, and iron (III) naphthoxide. The term "organoiron compound" refers to any iron compound containing at least one iron-carbon bond. Suitable organoiron compounds include bis(cyclopentadienyl)iron(II) (also called ferrocene), bis(pentamethylcyclopentadienyl)iron(II) (also called decamethylferrocene), bis (pentadienyl) iron (II) , bis (2,4-dimethylpentadienyl) iron (II) , bis(allyl)dicarbonyliron(II), (cyclopentadienyl) (pentadienyl) iron (II), tetra(l- norbornyl) iron (IN) , (trimethylenemethane) tricarbonyliron (II) , bis (butadiene) carbonyliron (0) , (butadiene) tricarbonyliron (0) , and bis (cyclooctatetraene) iron (0) .

Useful hydrogen phosphite compounds that can be employed as ingredient (b) of the iron-based catalyst composition are acyclic hydrogen phosphites, cyclic hydrogen phosphites, or mixtures thereof.

The acyclic hydrogen phosphites may be represented by the following keto-enol tautomeric structures:

where Rl and R^, which may be the same or different, are mono-valent organic groups. Preferably, R! and R^ 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 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, nitrogen, oxygen, silicon, sulfur, and phosphorus atoms. The acyclic 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 Rl and R^ 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 as ingredient (b) of the catalyst composition.

Suitable acyclic hydrogen phosphites are 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, dimenthyl 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.

The cyclic hydrogen phosphites 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 R3 is a divalent organic group. Preferably, R3 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 carbon atom, or the appropriate minimum number of carbon atoms to form these groups, up to 20 carbon atoms. These hydrocarbylene groups may contain heteroatoms such as, but not limited to, nitrogen, oxygen, silicon, sulfur, and phosphorus atoms. 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 type of R^ 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 employed as ingredient (b) of the catalyst composition.

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 side-product alcohol (usually methanol or ethanol) that results from the transesterification reaction leaves the new-made cyclic hydrogen phosphite.

Suitable cyclic alkylene hydrogen phosphites are 2-oxo-(2H)-5-butyl-5- ethyl-l,3,2-dioxaphosphorinane, 2-oxo-(2H)-5,5-dimethyl-l,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-l,3,2- dioxaphosphorinane, 2-oxo-(2H)-5,5-diethyl-l,3,2-dioxaphosphorinane, 2-oxo- (2H)-5-methyl-5-propyl-l,3,2-dioxaphosphorinane, 2-oxo-(2H)-4-isopropyl-5,5- dimethyl-l,3,2-dioxaphosphorinane, 2-oxo-(2H)-4,6-dimethyl-l,3,2- dioxaphosphorinane, 2-oxo-(2H)-4-propyl-5-ethyl-l,3,2-dioxaphosphorinane, 2- oxo-(2H)-4-methyl-l,3,2-dioxaphospholane, 2-oxo-(2H)-4,5-dimethyl-l,3,2- dioxaphospholane, 2-oxo-(2H)-4,4,5,5-tetramethyl-l,3,2-dioxaphospholane, and the like. Mixtures of the above cyclic alkylene hydrogen phosphites may also be utilized.

Suitable cyclic arylene hydrogen phosphites are 2-oxo-(2H)-4,5-benzo- 1,3,2-dioxaphospholane, 2-oxo-(2H)-4,5-(3^'-methylbenzo)-l,3,2- dioxaphospholane, 2-oxo-(2H)-4,5-(4-methylbenzo)-l,3,2-dioxaphospholane, 2- oxo-(2H)-4,5-(4^'-tert-butylbenzo)-l,3,2-dioxaphospholane, 2-oxo- (2H) -4,5- naphthalo-l,3,2-dioxaphospholane, and the like. Mixtures of the above cyclic arylene hydrogen phosphites may also be utilized.

The iron-based catalyst composition further comprises an organoaluminum compound, which has been designated as ingredient (c). As used herein, the term "organoaluminum compound" refers to any aluminum compound containing at least one covalent aluminum-carbon bond. It is generally advantageous to employ organoaluminum compounds that are soluble in a hydrocarbon solvent.

A preferred class of organoaluminum compounds that can be utilized is represented by the general formula AlR_nX3__n, where each R, which may be the same or different, is a mono-valent organic group, where each X, which may be the same or different, is a hydrogen atom, a carboxylate group, an alkoxide group, or an aryl oxide group, and where n is an integer of 1 to 3. Preferably, each R is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, aryl, aralkyl, alkaryl, and allyl groups, with each group preferably containing from 1 carbon atom, or the appropriate minimum number of carbon atoms to form these groups, up to about 20 carbon atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, nitrogen, oxygen, silicon, sulfur, and phosphorus atoms. Preferably, each X is a carboxylate group, an alkoxide group, or an aryloxide group, with each group preferably containing from 1 carbon atom, or the appropriate minimum number of carbon atoms to form these groups, up to about 20 carbon atoms. Suitable types of organoaluminum compounds that can be utilized include, but are not limited to, trihydrocarbylaluminum, dihydrocarbylaluminum hydride, hydrocarbylaluminum dihydride, dihydrocarbylaluminum carboxylate, hydrocarbylaluminum bis (carboxylate), dihydrocarbylaluminum alkoxide, hydrocarbylaluminum dialkoxide, dihydrocarbylaluminum aryloxide, hydrocarbylaluminum diaryloxide, and the like, and mixtures thereof. Trihydrocarbylaluminum compounds are generally preferred.

Examples of organoaluminum compounds that can be utilized include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n- propylaluminum, triisopropylaluminum, tri-n-butylaluminum, tri-n- hexylaluminum, tri-n-octylaluminum, tricyclohexylaluminum, triphenylaluminum, tri-p-tolylaluminum, tribenzylaluminum, diethylphenylaluminum, diethyl-p- tolylaluminum, diethylbenzylaluminum, ethyldiphenylaluminum, ethyldi-p- tolylaluminum, ethyldibenzylaluminum, diethylaluminum 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, phenylisopropylaluminum hydride, phenyl-n-butylaluminum hydride, phenylisobutylaluminum hydride, phenyl-n-octylaluminum hydride, p- tolylethylaluminum hydride, p-tolyl-n-propylaluminum 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-octylaluminum hydride, ethylaluminum dihydride, n-propylaluminum dihydride, isopropylaluminum dihydride, n-butylaluminum dihydride, isobutylaluminum dihydride, n- octylaluminum dihydride, dimethylaluminum hexanoate, diethylaluminum octoate, diisobutylaluminum 2-ethylhexanoate, dimethylaluminum neodecanoate, diethylaluminum stearate, diisobutylaluminum oleate, methylaluminum bis (hexanoate), ethylaluminum bis (octoate), isobutylaluminum bis (2- ethylhexanoate), methylaluminum bis (neodecanoate), 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, and the like, and mixtures thereof. Another class of organoaluminum compounds that can be utilized 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 R4, which may be the same or different, is a mono-valent organic group. Preferably, each R4 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 carbon atoms, or the appropriate minimum number of carbon atoms to form these groups, up to about 20 carbon atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, nitrogen, oxygen, silicon, sulfur, and phosphorus atoms. It should be noted that 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 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 oligomerized, and then water is added. Examples of 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 because of its availability and its solubility in aliphatic and cycloaliphatic hydrocarbon solvents. Modified methylaluminoxane can be formed by substituting about 20-80% of the methyl groups of methylaluminoxane with C2 to Cχ2 hydrocarbyl groups, preferably with isobutyl groups, by using techniques known to those skilled in the art.

The iron-based catalyst composition has a very high catalytic activity for polymerizing 1,3-butadiene into syndiotactic 1,2-polybutadiene 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, it is believed that the three catalyst ingredients (a), (b), and (c) 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 hydrogen phosphite to the iron-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 organoaluminum compound to the iron-containing compound (Al/Fe) can be varied from about 1:1 to about 100:1, more preferably from about 11:1 to about 50:1, even more preferably from about 12:1 to about 25:1, and still more preferably from about 15:1 to about 20:1.

The iron-based catalyst composition 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, the term "catalyst composition" has been employed to encompass a simple mixture of the ingredients, a complex of the 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 iron-based catalyst composition can be formed by combining or mixing the catalyst ingredients or components by using, for example, one of the following methods.

First, 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 iron-containing compound is added first, followed by the hydrogen phosphite, and finally followed by the organoaluminum compound. Second, the three catalyst ingredients may be pre-mixed outside the polymerization system at an appropriate temperature, which is generally from about -20°C to about 80°C, and the resulting catalyst composition is then added to the monomer solution.

Third, 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°C to about 80°C. The amount of monomer that is used for the catalyst pre-forming can range from about 1 to about 500, and preferably from about 4 to about 100 moles per mole of the iron-containing compound. The resulting catalyst composition is then added to the remainder of the monomer that is to be polymerized.

Fourth, the catalyst composition may be formed by using a two-stage procedure. The first stage involves reacting the iron-containing compound with the organoaluminum compound in the presence of a small amount of monomer at an appropriate temperature, which is generally from about -20 °C 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 remainder of the monomer that is to be polymerized.

Fifth, an alternative two-stage procedure may also be employed. An iron-ligand complex is first formed by pre-combining the iron-containing compound with the hydrogen phosphite. Once formed, this iron-ligand complex is then combined with the organoaluminum compound to form the active catalyst species. The iron-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 iron-ligand complex will depend upon several variables including the particular starting materials and the solvent employed. Once formed, the iron-ligand complex can be used without isolation from the complexation reaction mixture. If desired, however, the iron-ligand complex may be isolated from the complexation reaction mixture before use. When a solution of the iron-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. The 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. Desirably, an organic solvent that is inert with respect to the catalyst composition is used.

The total catalyst concentration of the iron-based catalyst composition to be employed in the polymerization mass depends on the interplay of various factors such as the purity of the ingredients, the polymerization temperature, the polymerization rate and conversion desired, and many other factors. Accordingly, the 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 iron-containing compound used can be varied from about 0.01 to about 2 mmol per 100 g of 1,3-butadiene monomer, with a more preferred range being from about 0.02 to about 1.0 mmol per 100 g of 1,3-butadiene monomer, and a most preferred range being from about 0.05 to about 0.5 mmol per 100 g of 1,3-butadiene monomer.

In performing the polymerization of 1,3-butadiene into the syndiotactic 1,2-polybutadiene cement, an amount of organic solvent is usually added to the polymerization system. This is in addition to the amount of organic solvent that may be used in preparing the iron-based catalyst composition. The additional organic solvent may be the same as or different from the organic solvent used in preparing the catalyst composition. It is generally preferred to employ a solution polymerization system in which both the 1,3-butadiene monomer to be polymerized and the syndiotactic 1,2-polybutadiene formed are soluble in the polymerization solvent. The ability to obtain a solution wherein the syndiotactic 1,2-polybutadiene product is dissolved within an organic solvent will vary based upon a number of factors including the melting temperature of the syndiotactic 1,2-polybutadeine, the concentration of the polymer within the solvent, the temperature of the solution, and the type of solvent employed. In general, a solution of syndiotactic 1,2-polybutaidene can be achieved by employing an aromatic solvent at a high temperature, e.g., syndiotactic 1,2-polybutaidene having a melting temperature of about 150°C is generally soluble in tolulene maintain at about 80°C. As disclosed in a co-pending application filed on February 20, 2002, (Attorney Docket No. P01077US1A) which is incorporated herein by reference, aliphatic solvents may also be employed as the polymerization medium so long as the melting temperature of the resultant syndiotactic 1,2-polybutadiene is below about 165°C and the polymerization medium is maintained at a temperature greater than about 65°C, which will provide a syndiotactic 1,2-polybutaidene cement in a supersaturated solution state. Blends of aromatic and aliphatic solvents may also be employed. The melting temperature of the resultant syndiotactic 1,2-polybutadiene can be controlled as disclosed in U.S. Patent No. 6,288,183, which is incorporated herein by reference.

The concentration of the 1,3-butadiene monomer to be polymerized is not limited to a special range. Preferably, however, the concentration of the 1,3- butadiene monomer present in the polymerization medium at the beginning of the polymerization should 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. In performing the polymerization of 1,3-butadiene into the syndiotactic

1,2-polybutadiene cement, a molecular weight regulator may be employed to control the molecular weight of the syndiotactic 1,2-polybutadiene to be produced. As a result, syndiotactic 1,2-polybutadiene having a wide range of molecular weights can be produced. Suitable types of molecular weight regulators 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-l,4- hexadiene, 1,5-cyclooctadiene, 3,7-dimethyl-l,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-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-butadiene monomer (phm), is preferably 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. In addition, the molecular weight of the syndiotactic 1,2-polybutadiene to be produced can also be effectively controlled by conducting the polymerization of 1,3-butadiene monomer in the presence of hydrogen gas. In this case, the partial pressure of hydrogen gas is preferably from about 0.01 to about 50 atmospheres. The polymerization of 1,3-butadiene into the syndiotactic 1,2- polybutadiene cement can be carried out as a batch process, a continuous process, or even a semi-continuous process. In the semi-continuous process, 1,3-butadiene monomer is intermittently charged as needed to replace that monomer already polymerized. The polymerization is desirably conducted under anaerobic conditions by using an inert protective gas such as nitrogen, argon or helium, with moderate to vigorous agitation. The 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 50 °C to about 90 °C. Where an aliphatic solvent is employed in a solution polymerization, especially where the resultant 1,2-polybutadiene has a melting temperature between about 120°C and 160°C, the polymerization is preferably conducted at a temperature in excess of about 65°C, more preferably in excess of about 70°C, and even more preferably in excess of about 80°C, in order to ensure that the resultant syndiotactic 1,2-polybutadiene product will remain in a supersaturated solution state. The heat of polymerization may be removed by external cooling, cooling by evaporation of the 1,3-butadiene 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 1 atmosphere to about 10 atmospheres. Once the syndiotactic 1,2-polybutadiene cement is prepared, it is preferred to inactivate the iron-based catalyst by adding a terminator prior to blending the syndiotactic 1,2-polybutadiene cement with the rubber cement. Typically, the terminator employed to inactivate the catalyst system is a protic compound, which includes, but is not limited to, an alcohol, a carboxylic acid, an inorganic acid, water, or a combination thereof. An antioxidant such as 2,6-di- tert-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 about 0.5% to 2% by weight of the syndiotactic 1,2-polybutadiene product.

Advantageously, the iron-based catalyst composition can be manipulated to vary the characteristics of the syndiotactic 1,2-polybutadiene in the polymer blend. Namely, the syndiotactic 1,2-polybutadiene can have various melting temperatures, molecular weights, 1,2-linkage contents, and syndiotacticities, all of which are dependent upon the selection of the catalyst ingredients and the ingredient ratios. For example, it has been found that the melting temperature, molecular weight, 1,2-linkage content, and syndiotacticity of the syndiotactic 1,2-polybutadiene can be increased by using an organoaluminum compound containing sterically bulky organic groups. Non-limiting examples of these sterically bulky organic groups include isopropyl, isobutyl, t-butyl, cyclohexyl, and 2,6-dimethylphenyl groups. The use of acyclic hydrogen phosphites in lieu of cyclic hydrogen phosphites will also increase the melting temperature, molecular weight, 1,2-linkage content, and syndiotacticity of the syndiotactic 1,2-polybutadiene. The manipulation of the characteristics of the syndiotactic 1,2-polybutadiene by varying catalyst ingredients and ratios is described in greater detail in U.S. Pat. Nos. 6,180,734, 6,211,313, 6,277,779, and 6,288,183. The syndiotactic 1,2-polybutadiene cement can be blended with the rubber cement by a variety of mechanical means. For example, the two cements can be blended in a blend tank with moderate to vigorous agitation. Those skilled in the art will appreciate the conditions required to ensure a solution of syndiotactic 1,2-polybutaidene from a solution polymerization should be maintained at least until blending with the rubber cement is started and, preferably, until the blending is completed. For example, where an aliphatic solvent is employed as the polymerization medium for the preparation of syndiotactic 1,2-polybutaidene having a melting temperature between about 120°C and 160°C, a temperature at least as high as the high temperature employed during polymerization should at least be maintained until blending has started. Likewise, where a high temperature is required to provide a solution of syndiotactic 1,2-polybutaidene within an aromatic solvent, this high temperature should be maintained at least until blending has started.

The blend of syndiotactic 1,2-polybutadiene and the rubbery elastomer can be recovered from the blended cement by utilizing conventional procedures of desolventization and drying. For instance, the blend of syndiotactic 1,2- polybutadiene and the rubbery elastomer may be isolated from the polymerization mixture by coagulation of the blended cement with an alcohol such as methanol, ethanol, or isopropanol, or by steam distillation of the solvent and the unreacted 1,3-butadiene monomer, followed by filtration. The product is then dried to remove residual amounts of solvent and water. The blend may also be isolated by directly drum drying the polymer cement, which subjects the polymers to temperatures in excess of 140°C. The polymer blend produced is a highly dispersed blend of crystalline syndiotactic 1,2-polybutadiene and the rubbery elastomer.

The blends of syndiotactic 1,2-polybutadiene and rubbery elastomers produced with the process of this invention 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. The blends of syndiotactic 1,2- polybutadiene and rubbery elastomers are also useful in the manufacture of films and packaging materials and in many molding applications. In order to demonstrate the practice of the present invention, the following examples have been prepared and tested. The examples should not, however, be viewed as limiting the scope of the invention. The claims will serve to define the invention. EXAMPLES Example 1

Polybutadiene rubber (BR) cement was prepared by polymerizing 1,3- butadiene in hexanes with n-butyllithium as the anionic initiator. A two-gallon stainless-steel reactor was charged with 1556 g of hexanes, 3433 g of a 1,3- butadiene/hexanes blend containing 21.8% by weight of 1,3-butadiene, and 5.99 mmol of n-butyllithium. The polymerization was carried out at 65 °C for 6 hours. The polymerization was terminated by adding 2 mL of isopropanol followed by 7.5 g of 2,6-di-tert-butyl-4-methylphenol. A small portion of the cement was removed from the reactor, and the conversion of the 1,3-butadiene monomer was determined to be essentially 100% by measuring the weight of the polymer recovered from the cement. The polybutadiene had a Mooney viscosity of 11.4. The Mooney viscosity (MLχ -j-4) was determined at 100°C with a Monsanto

Mooney viscometer using a large rotor, a one-minute warm-up time and a four- minute running time. As measured by differential scanning calorimetry (DSC), the polymer had a glass transition temperature (Tg) of -92 °C. The 1H nuclear magnetic resonance (NMR) analysis of the polymer indicated a 1,2-linkage content of 8.0%. As determined by gel permeation chromatography (GPC), the polymer had a number average molecular weight (M_n) of 123,000, a weight average molecular weight (M_w) of 132,000, and a polydispersity index (M_w/M_n) of 1.0

The remaining cement was maintained at 90 °C prior to blending with the syndiotactic 1,2-polybutadiene cement prepared in Example 4.

Example 2

Styrene-butadiene rubber (SBR) cement was prepared by copolymerizing 1,3-butadiene and styrene in hexanes with n-butyllithium/2,2- di(tetrahydrofuryl) propane as the anionic initiator. A two-gallon stainless-steel reactor was charged with 1848 g of hexanes, 2575 g of a 1,3-butadiene/hexanes blend containing 21.8% by weight of 1,3-butadiene, 567 g of a styrene/hexanes blend containing 33.0% by weight of styrene, 5.99 mmol of n-butyllithium, and 1.50 mmol of 2,2-di(tetrahydrofuryl)propane. The polymerization was carried out at 65 °C for 5 hours. The polymerization was terminated by adding 2 mL of isopropanol followed by 7.5 g of 2,6-di-tert-butyl-4-methylphenol. A small portion of the cement was removed from the reactor, and the conversion of the monomers was determined to be 97% by measuring the weight of the polymer recovered from the cement. The SBR had a Mooney viscosity of 23.4, a glass transition temperature of -42°C, a styrene content of 26.3%, a 1,2-linkage content of 40.1% for the butadiene units, a number average molecular weight of 121,000, a weight average molecular weight of 132,000, and a polydispersity index of 1.09. The remaining cement was maintained at 90 °C prior to blending with the syndiotactic 1,2-polybutadiene cement prepared in Example 4.

Example 3

A high cis-l,4-polybutadiene rubber (c£s-BR) cement was prepared by polymerizing 1,3-butadiene in hexanes with a neodymium-based catalyst. A two- gallon stainless-steel reactor was charged with 1623 g of hexanes, 2913 g of a 1,3- butadiene/hexanes blend containing 21.8% by weight of 1,3-butadiene, 21.5 mmol of triisobutylaluminum, 0.826 mmol of neodymium(III) neodecanoate, and 1.16 mmol of ethylaluminum dichloride. The polymerization was carried out at 85 °C for 2 hours. The polymerization was terminated by adding 6 mL of isopropanol followed by 6.4 g of 2,6-di-tert-butyl-4-methylphenol. A small portion of the cement was removed from the reactor, and the conversion of the 1,3- butadiene monomer was determined to be 96% by measuring the weight of the polymer recovered from the cement. The cis-BR had a Mooney viscosity of 24.7, a glass transition temperature of -104°C, a number average molecular weight of 100,000, a weight average molecular weight of 438,000, and a polydispersity index of 4.4.

The remaining cement was maintained at 90 °C prior to blending with the syndiotactic 1,2-polybutadiene cement prepared in Example 4. Example 4

Syndiotactic 1,2-polybutadiene (SPB) cement was prepared by polymerizing 1,3-butadiene in hexanes with an iron-based catalyst. A two-gallon stainless-steel reactor was charged with 2039 g of hexanes, 2497 g of a 1,3- butadiene/hexanes blend containing 21.8% by weight of 1,3-butadiene, 0.544 mmol of iron (III) 2-ethylhexanoate, 2.18 mmol of bis (2-ethylhexyl) hydrogen phosphite, and 7.62 mmol of tri-n-butylaluminum. The polymerization was carried out at 90 °C for 3 hours. The polymerization was terminated by adding 4 mL of isopropanol followed by 5.4 g of tris (nonylphenyl) phosphite and 20 g of 2,6-di-tert-butyl-4-methylphenol. A small portion of the cement was removed from the reactor, and the conversion of the 1,3-butadiene monomer to SPB was determined to be 95% by measuring the weight of the polymer recovered from the cement. The SPB had a melting temperature of 146°C, a 1,2-linkage content of 89.7%, a syndiotacticity of 81.6%, a number average molecular weight of 161,000, a weight average molecular weight of 340,000, and a polydispersity index of 2.1.

The remaining cement was maintained at 90 °C prior to blending with the rubber cements prepared in Examples 1-3.

Example 5

A blend of syndiotactic 1,2-polybutadiene and polybutadiene rubber was obtained by blending the BR cement prepared in Example 1 with the SPB cement prepared in Example 4. A 1 -liter glass bottle was capped with a self- sealing rubber liner and a perforated metal cap, purged with nitrogen, and then charged with 333 g of the BR cement. After the bottle was preheated to 90°C, 18.8 g of the hot SPB cement was charged into the bottle. The bottle was then shaken vigorously and then tumbled for 30 minutes in a water bath maintained at 90 °C. The blended cement was coagulated with 3 liters of isopropanol containing 1 g of tris (nonylphenyl) phosphite and 3 g of 2,6-di-tert-butyl-4-methylphenol. The resulting blend of syndiotactic 1,2-polybutadiene and polybutadiene was dried to a constant weight under vacuum at 60 °C. The polymer blend contained 4.3% SPB. It had a Mooney viscosity of 14.8, a glass transition temperature of - 92 °C resulting from BR, and a melting temperature of 143 °C resulting from SPB. The amounts of the cements used and the properties of the resulting polymer blend are summarized in Table I. Table I

Example 6 and 7

In Examples 6 and 7, the procedure described in Example 5 was repeated except that the amounts of the cement used were varied as shown in Table I. The amounts of the cements used and the properties of the resulting polymer blend are summarized in Table I.

Example 8 -10

In Examples 8-10, by using a similar procedure to that described in Example 5, a blend of syndiotactic 1,2-polybutadiene and styrene-butadiene rubber was obtained by blending the SBR cement prepared in Example 2 with the SPB cement prepared in Example 4. The amounts of the cements used and the properties of the resulting polymer blend are summarized in Table II.

Table II

Example 11 -13

In Examples 11-13, by using a similar procedure to that described in Example 5, a blend of syndiotactic 1,2-polybutadiene and high cis-1,4- polybutadiene was obtained by blending the cis-BR cement prepared in Example 3 with the SPB cement prepared in Example 4. The amounts of the cements used and the properties of the resulting polymer blend are summarized in Table III.

Table III

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 duly limited to the illustrative embodiments set forth herein.

Claims

CLAIMSWhat is claimed is:

1. A process for preparing blends of syndiotactic 1,2-polybutadiene and rubbery elastomers comprising the steps of: (1) providing a rubber cement that includes at least one rubbery elastomer in an organic solvent;

(2) providing a syndiotactic 1,2-polybutadiene cement that includes a solution of syndiotactic 1,2-polybutadiene in an organic solvent;

(3) blending the rubber cement with the syndiotactic 1,2-polybutadiene cement; and

(4) recovering the blend of syndiotactic 1,2-polybutadiene and the rubbery elastomer from the blended cement.

2. A rubbery elastomer/syndiotactic 1,2-polybutadiene blend prepared by a process comprising the steps of:

(1) providing a rubber cement that includes at least one rubbery elastomer in an organic solvent;

(2) providing a syndiotactic 1,2-polybutadiene cement that includes a solution of syndiotactic 1,2-polybutadiene in an organic solvent; (3) blending the rubber cement with the syndiotactic 1,2-polybutadiene cement; and

3. The process of claim 1, where the step of providing a rubber cement comprises the step of polymerizing one or more monomers in an organic solvent to form rubbery elastomers.

4. The process of claim 1, where the concentration of the rubbery elastomers within the rubber cement is from about 5% to about 35% by weight of the rubber cement.

5. The process of claim 1 or blend of claim 2, where said step of providing a syndiotactic 1,2-polybutadiene cement comprises the step of polymerizing 1,3- butadiene in an organic solvent in the presence of an iron-based catalyst composition that is formed by combining ingredients comprising: a) an iron containing compound; b) a hydrogen phosphite; and c) an organoaluminum compound.

6. The process of claim 5, where the organic solvent in which the step of polymerizing 1,3-butadiene takes place is an aliphatic solvent and the polymerization is conducted at a temperature in excess of 65°C.

7. The process of claim 5, wherein 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 Rl and R², which may be the same or different, are mono-valent organic groups, and where R3 is a divalent organic group.

8. The process of claim 5, wherein the organoaluminum compound is defined by the formula AlR_nX3-n_> where each R, which may be the same or different, is a mono-valent organic group, where each X, which may be the same or different, is a hydrogen atom, a carboxylate group, an alkoxide group, or an aryloxide group, and where n is an integer including 1, 2 or 3.

9. The process of claim 5, wherein the organoaluminum compound is an aluminoxane defined by one of the following formulas:

where x is an integer of 1 to about 100, y is an integer of 2 to about 100, and each R4, which may be the same or different, is a mono-valent organic group.

10. The process of claim 5, wherein the molar ratio of the hydrogen phosphite to the iron-containing compound is from about 0.5:1 to about 50:1, and the molar ratio of the organoaluminum compound to the iron-containing compound is from about 12:1 to about 100:1.