Iron-based catalyst for producing binary cis-1,4-/1,2-polybutadiene

A catalyst composition that is the combination of or the reaction product of ingredients including an iron-containing compound, an organomagnesium compound, and a cyclic hydrogen phosphite. This catalyst composition is particularly useful for polymerizing 1,3-butadiene into binary cis-1,4/1,2-polybutadiene.

FIELD OF THE INVENTION 
The present invention generally relates to a catalyst composition for use 
in polymerizing 1,3-butadiene into binary cis-1,4-/1,2-polybutadiene. More 
particularly, the present invention is directed toward an iron-based 
catalyst composition that is formed by combining an iron-containing 
compound, an organomagnesium compound, and a cyclic hydrogen phosphite. 
BACKGROUND OF THE INVENTION 
Binary cis-1,4-/1,2-polybutadiene is a polybutadiene rubber that has a 
microstructure in which the polymeric main chain consists almost 
exclusively of cis-1,4- and 1,2-units with almost no trans-1,4-units. 
Binary cis-1,4-/1,2-polybutadiene exhibits unique viscoelastic properties 
as compared to other synthetic rubbers. For instance, binary 
cis-1,4-/1,2-polybutadiene has higher green strength and higher tack than 
the polybutadiene having similar 1,2-linkage content that is made by 
anionic polymerization. Therefore, binary cis-1,4-/1,2-polybutadiene can 
be utilized in a variety of applications and is particularly useful as a 
tire rubber. It can also be blended into other synthetic rubbers and 
co-cured therewith. 
Binary cis-1,4-/1,2-polybutadiene cannot be produced by anionic 
polymerization utilizing alkyllithium initiators. Only a few coordination 
catalyst systems based on transition metals are known for the preparation 
of binary cis-1,4-/1,2-polybutadiene. For example, Polymer Journal, Volume 
2, page 371 (1971) discloses a process for polymerizing 1,3-butadiene into 
binary cis-1,4-/1,2-polybutadiene by using a catalyst system comprising 
cobalt tris(acetylacetonate), triethylaluminum, and water. Polymer 
Journal, Volume 5, page 231 (1973) discloses a process for preparing 
binary cis-1,4-/1,2-polybutadiene by polymerizing 1,3-butadiene in the 
presence of one of the four catalyst systems: (1) a catalyst system 
comprising dialkoxy molybdenum trichloride and trialkylaluminum, (2) a 
catalyst system comprising molybdenum pentachloride and triethylaluminum, 
(3) a catalyst system comprising dioxo molybdenum bis(acetylacetonate) and 
diethylaluminum chloride, and (4) a catalyst system comprising dioxo 
molybdenum bis(acetylacetonate), triethylaluminum, and a halogen compound 
such as ethylaluminum dichloride, carbon tetrabromide, t-butyl chloride, 
or iodine. U.S. Pat. No. 3,817,968 discloses a method of producing binary 
cis-1,4-/1,2-polybutadiene by polymerizing 1,3-butadiene in the presence 
of a catalyst system comprising dialkoxy molybdenum trichloride and 
trialkylaluminum, or a catalyst system comprising dioxo molybdenum 
bis(acetylacetonate) and dialkylaluminum chloride. Journal of Molecular 
Catalysis, Volume 17, page 65 (1982) discloses a process that produces 
binary cis-1,4-/1,2-polybutadiene by polymerizing 1,3-butadiene in the 
presence of a catalyst system comprising iron tris(acetylacetonate), 
triisobutylaluminum, and 1,10-phenanthroline. All of the aforementioned 
catalyst systems, however, have very low activity and therefore have no 
industrial utility. 
Because binary cis-1,4-/1,2-polybutadiene is useful and the catalyst 
systems known heretofore in the art have various shortcomings, it would be 
advantageous to develop a new and significantly improved catalysts that 
have high catalytic activity and stereoselectivity for polymerizing 
1,3-butadiene into binary cis-1,4-/1,2-polybutadiene. 
SUMMARY OF THE INVENTION 
In general, the present invention provides an iron-based catalyst 
composition that is the combination of or the reaction product of 
ingredients comprising an iron-containing compound, an organomagnesium 
compound, and a cyclic hydrogen phosphite. 
The present invention further provides an iron-based catalyst composition 
formed by a process comprising the step of combining an iron-containing 
compound, an organomagnesium compound, and a cyclic hydrogen phosphite. 
The present invention also provides a process for producing binary 
cis-1,4-/1,2-polybutadiene comprising the step of polymerizing 
1,3-butadiene in the presence of a catalytically effective amount of a 
catalyst composition formed by a process comprising the step of combining 
an iron-containing compound, an organomagnesium compound, and a cyclic 
hydrogen phosphite. 
The present invention also provides a cis-1,4-/1,2-polybutadiene polymer 
that is prepared by polymerizing 1,3-butadiene with a catalyst composition 
formed by a process comprising the step of combining an iron-containing 
compound, an organomagnesium compound, and a cyclic hydrogen phosphite. 
Advantageously, the catalyst composition of the present invention has very 
high catalytic activity and stereoselectivity for polymerizing 
1,3-butadiene into binary cis-1,4-/1,2-polybutadiene. This activity and 
selectivity, among other advantages, allows binary 
cis-1,4-/1,2-polybutadiene to be produced in very high yields with low 
catalyst levels after relatively short polymerization times. 
Significantly, the catalyst composition of this invention is iron-based, 
and iron compounds are generally stable, inexpensive, relatively 
innocuous, and readily available. Additionally, the catalyst composition 
of this invention has high catalytic activity in a wide variety of 
solvents including the environmentally-preferred nonhalogenated solvents 
such as aliphatic and cycloaliphatic hydrocarbons. 
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
The present invention is directed toward a catalyst composition that can be 
employed to synthesize cis-1,4-/1,2-polybutadiene. It has now been found 
that cis-1,4-/1,2-polybutadiene can be efficiently synthesized by 
polymerizing 1,3-butadiene in the presence of an iron-based catalyst 
composition. The catalyst composition of the present invention is formed 
by combining (a) an iron-containing compound, (b) an organomagnesium 
compound, and (c) a cyclic hydrogen phosphite. In addition to the three 
catalyst ingredients (a), (b), and (c), other organometallic compounds or 
Lewis bases can be added, if desired. 
Various iron-containing compounds or mixtures thereof can be employed as 
ingredient (a) of the catalyst composition of this invention. It is 
generally advantageous to employ iron-containing compounds that are 
soluble in hydrocarbon solvents such as aromatic hydrocarbons, aliphatic 
hydrocarbons, or cycloaliphatic hydrocarbons. Hydrocarbon-insoluble 
iron-containing compounds, however, can be suspended in the polymerization 
medium to form the catalytically active species, and are therefore 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. It is preferable to use divalent iron compounds (also called 
ferrous compounds), wherein the iron is in the +2 oxidation state, and 
trivalent iron compounds (also called ferric compounds), wherein the iron 
is in the +3 oxidation state. Suitable types of iron-containing compounds 
that can be utilized in the catalyst composition of this invention 
include, but are not limited to, iron carboxylates, iron carbamates, iron 
dithiocarbamates, iron xanthates, iron .beta.-diketonates, iron alkoxides 
or aryloxides, iron halides, iron pseudo-halides, iron oxyhalides, and 
organoiron compounds. 
Some specific examples of 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. 
Some specific examples of 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. 
Some specific examples of 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. 
Some specific examples of 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. 
Some specific examples of suitable iron .beta.-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. 
Some specific examples of 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. 
Some specific examples of suitable iron halides include iron(II) fluoride, 
iron(III) fluoride, iron(II) chloride, iron(III) chloride, iron(II) 
bromide, iron(III) bromide, and iron(II) iodide. Some representative 
examples of suitable iron pseudo-halides include iron(II) cyanide, 
iron(III) cyanide, iron(II) cyanate, iron(III) cyanate, iron(II) 
thiocyanate, iron(III) thiocyanate, iron(II) azide, iron(III) azide, and 
iron(III) ferrocyanide (also called Prussian blue). Some representative 
examples of suitable iron oxyhalides include iron(III) oxychloride and 
iron(III) oxybromide. 
The term "organoiron compound" refers to any iron compound containing at 
least one iron-carbon bond. Some specific examples of 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(1-norbornyl)iron(IV), 
(trimethylenemethane)tricarbonyliron(II), bis(butadiene)carbonyliron(0), 
butadienetricarbonyliron(0), and bis(cyclooctatetraene)iron(0). 
Various organomagnesium compounds or mixtures thereof can be utilized as 
ingredient (b) of the catalyst composition of this invention. As used 
herein, the term "organomagnesium compound" refers to any magnesium 
compound that contains at least one magnesium-carbon bond. It is generally 
advantageous to employ organomagnesium compounds that are soluble in a 
hydrocarbon solvent. 
A preferred class of organomagnesium compounds that can be utilized is 
represented by the general formula MgR.sup.1.sub.2, where each R.sup.1, 
which may be the same or different, is a mono-valent organic group, with 
the proviso that the group is attached to the magnesium atom via a carbon 
atom. Preferably, each R.sup.1 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 atom, or the appropriate minimum number of carbon 
atoms to form the group, up to about 20 carbon atoms. These hydrocarbyl 
groups may contain heteroatoms such as, but not limited to, nitrogen, 
oxygen, silicon, sulfur, and phosphorus atom. 
Some specific examples of suitable dihydrocarbylmagnesium compounds that 
can be utilized include diethylmagnesium, di-n-propylmagnesium, 
diisopropylmagnesium, dibutylmagnesium, dihexylmagnesium, 
diphenylmagnesium, dibenzylmagnesium, and the like, and mixtures thereof. 
Dibutylmagnesium is particularly useful due to its availability and its 
solubility in aliphatic and cycloaliphatic hydrocarbon solvents. 
Another class of organomagnesium compounds that can be utilized is 
represented by the general formula R.sup.2 MgX, where R.sup.2 is a 
mono-valent organic group, with the proviso that the group is attached to 
the magnesium atom via a carbon atom, and X is a hydrogen atom, a halogen 
atom, a carboxylate group, an alkoxide group, or an aryloxide group. 
Preferably, R.sup.2 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 
atom, or the appropriate minimum number of carbon atoms to form the group, 
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, X is a carboxylate group, an 
alkoxide group, or an aryloxide group, with each group preferably 
containing 1 to 20 carbon atoms. 
Suitable types of organomagnesium compounds that are represented by the 
general formula R.sup.2 MgX include, but are not limited to, 
hydrocarbylmagnesium hydride, hydrocarbylmagnesium halide, 
hydrocarbylmagnesium carboxylate, hydrocarbylmagnesium alkoxide, 
hydrocarbylmagnesium aryloxide, and mixtures thereof. 
Some specific examples of suitable organomagnesium compounds that are 
represented by the general formula R.sup.2 MgX include methylmagnesium 
hydride, ethylmagnesium hydride, butylmagnesium hydride, hexylmagnesium 
hydride, phenylmagnesium hydride, benzylmagnesium hydride, methylmagnesium 
chloride, ethylmagnesium chloride, butylmagnesium chloride, hexylmagnesium 
chloride, phenylmagnesium chloride, benzylmagnesium chloride, 
methylmagnesium bromide, ethylmagnesium bromide, butylmagnesium bromide, 
hexylmagnesium bromide, phenylmagnesium bromide, benzylmagnesium bromide, 
methylmagnesium hexanoate, ethylmagnesium hexanoate, butylmagnesium 
hexanoate, hexylmagnesium hexanoate, phenylmagnesium hexanoate, 
benzylmagnesium hexanoate, methylmagnesium ethoxide, ethylmagnesium 
ethoxide, butylmagnesium ethoxide, hexylmagnesium ethoxide, 
phenylmagnesium ethoxide, benzylmagnesium ethoxide, methylmagnesium 
phenoxide, ethylmagnesium phenoxide, butylmagnesium phenoxide, 
hexylmagnesium phenoxide, phenylmagnesium phenoxide, benzylmagnesium 
phenoxide, and the like, and mixtures thereof. 
Various cyclic hydrogen phosphites or mixtures thereof can be utilized as 
ingredient (c) of the catalyst composition of this invention. In general, 
cyclic hydrogen phosphites contain a divalent organic group that bridges 
between the two oxygen atoms that are singly-bonded to the phosphorus 
atoms. These cyclic hydrogen phosphites may be represented by the 
following keto-enol tautomeric structures: 
##STR1## 
where R.sup.3 is a divalent organic group. Preferably, R.sup.3 is a 
hydrocarbylene group such as, but not limited to, alkylene, cycloalkylene, 
substituted alkylene, substituted cycloalkylene, alkenylene, 
cycloalkenylene, substituted alkenylene, substituted cycloalkenylene, 
arylene, and substituted arylene groups, with each group preferably 
containing from 1 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, 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 types of R.sup.3 
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 the ingredient 
(c) of the catalyst composition of this invention. 
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. 
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-(2H)-4,6-dimethyl-1,3,2-dioxaphosphorinane, 
2-oxo-(2H)-4-propyl-5-ethyl-1,3,2-dioxaphosphorinane, 2-oxo-(2H) 
-4-methyl-1,3,2-dioxaphospholane, 2-oxo-(2H) 
-4,5-dimethyl-1,3,2-dioxaphospholane, 
2-oxo-(2H)-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane, and the like. 
Mixtures of 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'-tert-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. 
The catalyst composition of this invention has a very high catalytic 
activity for polymerizing 1,3-butadiene into binary 
cis-1,4-/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 catalyst concentrations and catalyst ingredient ratios. Further, it is 
believe 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 catalyst ingredients. The molar ratio of the organomagnesium 
compound to the iron-containing compound (Mg/Fe) 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 25:1. The molar ratio of the 
cyclic 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. 
As discussed above, the catalyst composition of the present invention is 
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 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: 
First, the catalyst composition may be formed in situ by adding the three 
catalyst ingredients to a solution containing the monomer and solvent, or 
simply bulk monomer, in either a stepwise or simultaneous manner. When 
adding the catalyst ingredients in a stepwise manner, the order in which 
the catalyst ingredients are added is not critical. Preferably, however, 
the organomagnesium compound is added first, followed by the 
iron-containing compound, and finally followed by the cyclic hydrogen 
phosphite. 
Second, the three catalyst ingredients may be pre-mixed outside the 
polymerization system at an appropriate temperature, which is generally 
from about -20.degree. C. to about 80.degree. 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 
1,3-butadiene monomer. That is, the three catalyst ingredients are 
pre-mixed in the presence of a small amount of 1,3-butadiene monomer at an 
appropriate temperature, which is generally from about -20.degree. C. to 
about 80.degree. C. The amount of 1,3-butadiene monomer that is used for 
the catalyst pre-forming can range from about 1 to about 500 moles per 
mole of the iron-containing compound, and preferably should be 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 
1,3-butadiene monomer that is to be polymerized. 
Fourth, as a further variation, the catalyst composition can also be formed 
by using a two-stage procedure. The first stage involves combining the 
iron-containing compound and the organomagnesium compound in the presence 
of a small amount of 1,3-butadiene monomer at an appropriate temperature, 
which is generally from about -20.degree. C. to about 80.degree. 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 1,3-butadiene 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 and the cyclic hydrogen phosphite compound. Once formed, this 
iron-ligand complex is then combined with the organomagnesium compound to 
form the active catalyst species. The iron-ligand complex can be formed 
separately or in the presence of the 1,3-butadiene 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 preferred to perform this reaction at room temperature or above. The 
time required for the formation of the iron-ligand complex is usually 
within the range of about 10 minutes to about 2 hours after mixing the 
iron-containing compound with the hydrogen phosphite compound. 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 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, diethylbenzene, mesitylene, and the like. 
Non-limiting examples of aliphatic hydrocarbon solvents include n-pentane, 
n-hexane, n-heptane, n-octane, n-nonane, n-decane, isopentane, isohexanes, 
isopentanes, isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene, 
petroleum spirits, and the like. And, non-limiting examples of 
cycloaliphatic hydrocarbon solvents include cyclopentane, cyclohexane, 
methylcyclopentane, 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. 
As described above, the catalyst composition of this invention exhibits 
very high catalytic activity for the polymerization of 1,3-butadiene into 
binary cis-1,4-/1,2-polybutadiene. Hence, the present invention further 
provides a process for producing binary cis-1,4-/1,2-polybutadiene by 
using the catalyst composition of this invention. Although the preferred 
embodiments of this invention are directed toward employing the catalyst 
composition of this invention to polymerize 1,3-butadiene into binary 
cis-1,4-/1,2-polybutadiene, the catalyst composition can be used to 
polymerize other conjugated dienes. 
The production of binary cis-1,4-/1,2-polybutadiene according to this 
invention is accomplished by polymerizing 1,3-butadiene monomer in the 
presence of a catalytically effective amount of the foregoing catalyst 
composition. 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 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, 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. 
The polymerization of 1,3-butadiene 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 
1,3-butadiene monomer to be polymerized and the polymer formed are soluble 
in the polymerization medium. Alternatively, a precipitation 
polymerization system may be employed by choosing a solvent in which the 
polymer formed is insoluble. In both cases, an amount of the organic 
solvent in addition to the organic solvent that may be used in preparing 
the iron-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, isopentanes, 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 environmental reasons, aliphatic and cycloaliphatic 
solvents are highly preferred. 
The concentration of the 1,3-butadiene monomer to be polymerized is not 
limited to a special range. Generally, however, it is preferred that the 
concentration of the 1,3-butadiene monomer 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 1,3-butadiene 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 1,3-butadiene according to this 
invention, a molecular weight regulator may be employed to control the 
molecular weight of the binary cis-1,4-/1,2-polybutadiene 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 binary 
cis-1,4-/1,2-polybutadiene having a wide range of molecular weights. 
Suitable types of molecular weight regulators that can be utilized 
include, but are not limited to, .alpha.-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-norbomene, 
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 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 binary cis-1,4-/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 according to this invention may be 
carried out as a batch process, a continuous process, or a semi-continuous 
process. In the semi-continuous process, 1,3-butadiene 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 nitrogen, 
argon or helium, with moderate to vigorous agitation. The polymerization 
temperature may vary widely from a low temperature, such as -10.degree. C. 
or below, to a high temperature such as 100.degree. C. or above, with a 
preferred temperature range being from about 20.degree. C. to about 
90.degree. C. 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 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 to inactivate the catalyst 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 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 usually in the range of 0.2% to 1% by weight of the polymer 
product. When the polymerization has been stopped, the binary 
cis-1,4-/1,2-polybutadiene can be recovered from the polymerization 
mixture by utilizing conventional procedures of desolventization and 
drying. For instance, the binary cis-1,4-/1,2-polybutadiene may be 
isolated from the polymerization mixture by coagulation of the 
polymerization mixture with an alcohol such as methanol, ethanol, or 
isopropanol, or by steam distillation of the solvent and the unreacted 
1,3-butadiene monomer, followed by filtration. The product is then dried 
to remove residual amounts of solvent and water. 
The binary cis-1,4/1,2-polybutadiene synthesized according to this 
invention advantageously has a trans-1,4 content that is less than about 5 
percent, preferably less than 3 percent, and even more preferably less 
than 2 percent. Advantageously, the catalyst composition of this invention 
can be manipulated to vary the characteristics of the resulting binary 
cis-1,4-/1,2-polybutadiene. For example, the microstructure of the binary 
cis-1,4-/1,2-polybutadiene made utilizing the catalyst composition of this 
invention can be varied by changing the catalyst ingredients and the 
ingredient ratios. As a general rule, as the molar ratio of the 
organomagnesium compound to the iron-containing compound is increased, the 
1,2-linkage content of the resulting binary cis-1,4-/1,2-polybutadiene 
increases, accompanied by a decrease in the cis-1,4-linkage content. By 
selecting the proper catalyst ingredients and the ingredient ratios, the 
catalyst composition of this invention can be utilized to prepare 
equibinary cis-1,4-/1,2-polybutadiene that generally consists of about 
equal amounts of cis-1,4- and 1,2-units with almost no trans-1,4-units. 
Namely, for purposes of this specification, the term equibinary 
cis-1,4-/1,2-polybutadiene refers to a microstructure that includes from 
about 45 to about 55 percent cis-1,4 units, from about 55 to about 45 
percent 1,2 units, and less than about 5 percent trans-1,4 units. 
The binary cis-1,4-/1,2-polybutadiene produced with the catalyst 
composition of this invention has higher green strength and higher tack 
than the polybutadiene having similar 1,2-linkage content that is made by 
anionic polymerization utilizing alkyllithium initiators. The binary 
cis-1,4-/1,2-polybutadiene has many applications and is particularly 
useful as atire rubber. The binary cis-1,4-/1,2-polybutadiene can also be 
blended into other synthetic rubbers and co-cured therewith. Vulcanized 
rubber compositions obtained from the binary cis-1,4-/1,2-polybutadiene of 
this invention have good resilience and high abrasion resistance without 
losing wet-skid resistance.

In order to demonstrate the practice of the present invention, the 
following examples have been prepared and tested as described in the 
General Experimentation Section disclosed hereinbelow. The examples should 
not, however, be construed as limiting the scope of the invention. The 
claims will serve to define the invention. 
GENERAL EXPERIMENTATION 
EXAMPLE 1 
In this experiment, a cyclic hydrogen phosphite was synthesized by the 
transesterification reaction of an acyclic dihydrocarbyl hydrogen 
phosphite with an alkylene diol. 
Dimethyl hydrogen phosphite (76.3 g, 0.693 mol) and 
2-butyl-2-ethyl-1,3-propanediol (110.0 g, 0.687 mol) were mixed in a 
round-bottom reaction flask that was connected to a distillation head and 
a receiving flask. The reaction flask was kept under an atmosphere of 
argon and placed in a silicone oil bath maintained at 150.degree. C. The 
transesterification reaction proceeded as indicated by the distillation of 
methanol. After about 2 hours of heating at the above temperature, the 
remaining methanol and any unreacted starting materials were removed by 
vacuum distillation at 135.degree. C. and a pressure of 150 torr. The 
remaining crude product was distilled at 160.degree. C. and a pressure of 
2 torr, yielding 2-oxo-(2H)-5-butyl-5-ethyl-1,3,2-dioxaphosphorinane as a 
very viscous, colorless liquid (128.8 g, 0.625 mol, 91% yield). The proper 
identity of the product was established by nuclear magnetic resonance 
(NMR) spectroscopic analyses. .sup.1 H NMR data (CDCl.sub.3, 25.degree. 
C., referenced to tetramethylsilane): .delta. 6.88 (doublet, .sup.1 
J.sub.HP =675 Hz, 1H, H-P), 4.1 (complex, 4H, OCH.sub.2), 0.8-1.8 
(complex, 14H, Et and Bu). .sup.13 P NMR data (CDCl.sub.3, 25.degree. C., 
referenced to external 85% H.sub.3 PO.sub.4): .delta. 3.88 (doublet of 
multiplets, .sup.1 J.sub.HP =670 Hz). 
EXAMPLE 2 
An oven-dried 1-liter 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 227 g of a 
1,3-butadiene/hexanes blend containing 22.0% by weight of 1,3-butadiene. 
The following catalyst components were added to the bottle in the 
following order: (1) 0.60 mmol of dibutylmagnesium, (2) 0.15 mmol of 
iron(III) acetylacetonate, and (3) 0.45 mmol of 
2-oxo-(2H)-5-butyl-5-ethyl-1,3,2-dioxaphosphorinane. The bottle was 
tumbled for 4 hours in a water bath maintained at 65.degree. C. The 
polymerization was terminated by addition of 10 mL of isopropanol 
containing 1.0 g of 2,6-di-tert-butyl-4-methylphenol. The polymerization 
mixture was coagulated with 3 liters of isopropanol. The resulting binary 
cis-1,4-/1,2-polybutadiene was isolated by filtration and dried to a 
constant weight under vacuum at 60.degree. C. The yield of the polymer was 
48.8 g (98% yield). As measured by differential scanning calorimetry 
(DSC), the polymer had a glass transition temperature of -63.degree. C. 
and had no melting temperature. The infrared spectroscopic analysis of the 
polymer indicated a cis-1,4-linkage content of 52.5%, a 1,2-linkage 
content of 44.5%, and a trans-1,4-linkage content of 3.0%. As determined 
by gel permeation chromatography (GPC), the polymer had a weight average 
molecular weight (M.sub.W) of 236,000, a number average molecular weight 
(M.sub.N) of 112,000, and a polydispersity index (M.sub.W /M.sub.N) of 
2.1. The monomer charge, the amounts of the catalyst ingredients, and the 
properties of the resulting binary cis-1,4-/1,2-polybutadiene are 
summarized in Table I. 
TABLE I 
______________________________________ 
Example No. 2 3 4 5 
______________________________________ 
22.0% 1,3-Bd/hexanes (g) 
227 227 227 227 
MgBu.sub.2 (mmol) 
0.60 0.75 0.90 1.05 
Fe(acac).sub.3 (mmol) 
0.15 0.15 0.15 0.15 
Cyclic hydrogen phosphite* 
0.45 0.45 0.45 0.45 
(mmol) 
Fe/Mg/P molar ratio 
1:4:3 1:5:3 1:6:3 1:7:3 
Polymer yield (%) after 4 hr at 
98 98 97 92 
65.degree. C. 
Glass transition temperature (.degree. C.) 
-63 -62 -62 -63 
Polymer microstructure: 
cis-1,4-linkage content (%) 
52.5 49.0 46.9 45.3 
1,2-linkage content (%) 
44.5 48.2 50.6 52.9 
trans-1,4-linkage content (%) 
3.0 2.8 2.5 1.8 
M.sub.w 236,000 267,000 238,000 
274,000 
M.sub.n 112,000 113,000 111,000 
99,000 
M.sub.w /M.sub.n 2.1 2.4 2.1 2.8 
______________________________________ 
*The cyclic hydrogen phosphite used was 
2oxo-(2H)-5-butyl-5-ethyl-1,3,2-dioxaphosphorinane. 
EXAMPLES 3-5 
In Examples 3-5, the procedure described in Example 2 was repeated except 
that the catalyst ingredient ratio was varied as shown in Table I. The 
monomer charge, the amounts of the catalyst ingredients, and the 
properties of the binary cis-1,4-/1,2-polybutadiene produced in each 
example are summarized in Table I. 
As can be seen in Table I, as the molar ratio of the organomagnesium 
compound to the iron-containing compound is increased, the 1,2-linkage 
content of the resulting binary cis-1,4-/1,2-polybutadiene increases, 
accompanied by a decrease in the cis-1,4-linkage content. 
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.