Stereoregular diene polymerization with inorganic catalysts. I. cis 1,4-Polymerization of 1,3-butadiene with a cobaltous chloride–aluminum chloride complex

JOURNAL OF POLYMER SCIENCE: PART A VOL. 2, PP. 3233-3255 (1964)

Stereoregular Diene Polymerization with Inorganic Catalysts. I. cis 1,P-Polymerization of 1,3-

Butadiene with a Cobaltous Chloride-Aluminum Chloride Complex

HARVEY SCOTT,* ROBERT E. FROST,? ROGER F. BELT,$ Goodrich-Gulf Chemicals, Inc., The B. F . Goodrich Research Center,

Brecksville, Ohio, and D. E. O’REILLY,§ GulJ Research and Development Company, Pittsburgh, Pennsylvania

Synopsis

The polymerization of l13-butadiene with several catalytic CoCl~-AlC13 compositions is described. Blue solid products of the reaction of CoClz with AlCls, in which Co is coordinated in an octahedral configuration, are ineffective as stereospecific catalysts, unless they are treated with an aromatic hydrocarbon to yield a solution of a mixture of a green catalytic Co(AlCl& complex, in which the Co coordination has a square planar configuration, and MC13 which is comparatively inert under polymerization conditions. This mixture forms regardless of the resulting (and frequent varying) molar ratio of A1 to Co in solution, and regardless of whether the solid products contain A1C4 that is not complexed with Co. Similar solutions result from the reaction of CoCL with AlClr in an aromatic hydrocarbon. In the absence of a modifier a benzene solution of a Co- (AlC14)z complex catalyzes stereoregular and nonstereoregular polymerizations to about an equal extent. However, the addition of thiophene favors cis polymerization at the expense of the nonstereoregular polymerization, and a quantitative yield of polybutadiene with 94-99% of its unsaturation in the cis configuration and a sulfur content corresponding to one thiophene endgroup per polymer molecule was thereby obtained. Cis content and conversion reached a maximum at thiophene levels of 300 mole-% based on AICl,. At lower thiophene levels, conversion, unlike cis content, passed through a minimum before reaching a maximum. Polymers with a similarly high cis content were also obtained in the absence of thiophene by preparing oily catalyst compositions in toluene or xylene in the presence of traces of aluminum, magnesium or zinc powders which are believed to serve mainly as proton scavengers. The stereospecificity of the catalytic solutions was esbentially independent of the ratio of Al to Co in solution. A possible mechanism consistent with polymerization data is discussed. It is suggested that stereoregular polymerization involves tahe attachment of thiophene and butadiene to one aluminum atom of the Co(AlCl4)~ complex in which Co is coordinated in a square planar configuration, by displacement of chloride ions from this aluminum atom to vacant coordination positions about the cobalt atom, resulting in an octahedral con-

* Present address: The Franklin Institute Laboratories, Philadelphia, Pennsylvania. i Present address: Chemistry Department, State University of New York at Albany

$ Present address: The Harshaw Chemical Company, Cleveland, Ohio. Albany, New York.

Present address: Argonne National Laboratory, Argonne, Illinois. 3233

3234 SCOTT, FROST, BELT, AND O'REILLY

figuration about cobalt, followed by a cycloalkylation reaction between the coordinated thiophene and butadiene and subsequent insertion of butadiene into the polymer chain by a sequence of similar cycloalkylation reactions.

INTRODUCTION

Although there may be no agreement about the exact composition of the catalytic species involved in the polymerization with Ziegler catalysts, it is generally conceded to involve a coordination complex of a transition metal salt and an organometallic compound.'' Generally, the organometallic component is added during the preparation of the catalyst, but it may also be formed in situ by reduction of monomer, especially when one catalyst component is an active metal or a metal hydride.lb We now wish to describe a stereoregular cis polymerization of butadiene which, our findings suggest, involves no reduction and is catalyzed by a soluble CoC12-A1CL coordination complex which can be considered an inorganic catalyst in the same sense that aluminum halides are considered inorganic catalysts for numerous conventional alkylation reactions. This complex has a cationic nonstereospecific catalytic activity similar to that of aluminum halides2* and other Lewis acid^,^,^ as well as &-directing prop- erties in the polymerization of l13-butadiene. The catalytic activity becomes almost completely stereospecific, however, on adding a small amount of thiophene, or by preparing the catalyst in the presence of traces of powdered aluminum or other metals.

A solid complex was obtained by chemisorption of AlCl, on CoClz or by fusing the components together in a sealed tube. Catalytic solutions and oils were obtained from the solid complex or the uncomplexed components in the presence of an aromatic hydrocarbon. Benzene was the best solvent for preparing solutions. The oils were prepared in toluene or xylene and their formation was facilitated by the presence of a trace of A1 powder which is believed to serve mainly as a proton scavenger. Two types of CO(AIC~~)~ complexes have been identified.4 One type was obtained in the solid state and the catalytically active type was formed only in solution. The complex which was isolated as a blue solid contains Co in an octahedral configuration.* It is not effective as a cisdirecting catalyst unless it is treated with an aromatic hydrocarbon to yield a solution of a mixture of the Co(A1C14)2 complex which is catalytically active and AlC18 which is comparatively unreactive under stereoregular polymerization condition^.^ Similar solutions were formed by the interaction of AlCl, with CoClz in an aromatic hydrocarbon. The active complex is green and contains Co in a square planar c~nfiguration.~ The nature and composition of the catalytic component of these solutions could not be determined by analyzing the variable elemental content of these solutions. The active complex was identified by magnetic resonance spectroscopy, whereupon it was also found that solutions of this complex always contained AlCl, regardless of the method of preparation, of the ratios of A1 to Co in solution or in the solid(s) used to prepare the solutions, and of

STEREOREGULAR DIENE POLYMERIZATION. I 3235

whether none, some or all of the AlCI, contained in the solid(s) was complexed with CoC12. The stereospecificity of these catalytic solutions was essentially independent of the ratio of A1 to Co in solution.

An examination of the results of this and particularly the spectroscopic investigation4 suggests a polymerization mechanism which is somewhat different from those proposed for the stereoregular cis polymerization of dienes with organometallic catalysts.

EXPERIMENTAL

All procedures were carried out in an atmosphere of dry nitrogen in glassware dried at 130°C. and cooled under nitrogen.

Reagents

Anhydrous AlCl, (J. T. Baker, reagent grade) generally was used as received, although it was purified in certain cases by sublimation after it had been heated with A1 powder in a sealed tube at 300°C. Anhydrous C0C12 was obtained by dehydration of CoClz.6H20 (Baker and Adamson, reagent grade), first in an oven a t 130°C. and finally a t 300°C. in a stream of dry nitrogen. Thiophene (Eastman, reagent grade) was dried over anhydrous MgSO4. Aluminum powder (Aloca Pigment 120) was used as received. Thiophene-free benzene was passed over Linde 4A molecular sieves and then refluxed with Na-K alloy and benzophenone before distillation. Butadiene (Phillips, Special Purity) was dried by passage over 4A molecular sieves.

Fused Complexes

Although the molar ratio of the components in the charge did not appear to be particularly critical with respect to the catalytic activity of solutions derived from these solids, the ratio most commonly used was the same as that of components in the pure CoC12-2A1C13 complex. This procedure, however, did not lead to complete conversion to complex. Sometimes, blue needles of pure complex would form as a top layer on cooling the melt slowly. The complex was stable in the molten state only if AlC13 was not allowed to escape.

C0C12 and A1C13 were fused in a sealed tube a t 20CL3OO"C.

Chemisorbed Complex

Powdered CoClz was exposed to AlCl, vapor a t 200-300°C. for several hours in a sealed system. The AlC& vapor was produced by heating AIClj in a separate compartment within this sealed system. Up to about 25 mole-'% AlC& was found in the product. X-ray analysis indicated the product to contain only one ~ o m p l e x ~ . ~ and excess CoC1,. Although A1C1, continued to be chemisorbed upon prolonged exposure, it also departed from the solid product in the form of volatile complex, and thus the analysis of the solid product did not reflect the progress of the chemisorption be-

3236 SCOTT, FROST, BELT, AND O’REILLY

yond this point. Exhaustive chemisorption volatilized all the CoClz in the form of complex if enough AICI, was provided.

Distilled Complex

Blue vapors which appeared in the aforementioned preparations were condensed under appropriate conditions. A somewhat crude fractional distillation of the condensate was accomplished by using a straight tube, melting the sample by heating the lower third of the tube in an oil bath, passing the vapors very slowly through the center of the tube which was surrounded by separated strips of aluminum foil in a “zebra” fashion to provide alternating warmer and cooler surfaces with both becoming cooler the greater their distance from the oil surface, and collecting the solid distillate settling in the tube from the top downwards. The least volatile fraction had the highest complex content and tended to have needles of pure complex sticking out of it.

Catalytic Oils

These were obtained as a brown-black separate phase by stirring a mixture of A1CI3 and CoC12, or any of the aforementioned solid products, with an aromatic hydrocarbon at room temperature for several hours or at elevated temperatures for at least a few minutes. Oil formation was accelerated by the presence of A1 powder and/or by using alkylated benzenes as solvents. Instead of Al, powdered Mg and Zn metals were also used in the preparation of these oils.

Catalytic Solutions

The method of preparation was the Same as that of the oils except that it required the absence of aluminum powder and the use of a less alkylated benzene, preferably benzene, as the solvent. Although the emerald green color of the dissolved complex soon appeared in the supernatant liquid by stirring the reactants with the solvent at room temperature, heating the mixture to 8OOC. accelerated solution. Benzene solutions were stable and useful for long periods, but on standing their color gradually darkened until eventually insoluble, dark oils formed. Toluene solutions were less stable, and the existence of xylene solutions was transient at best as oils formed within a few minutes of contacting the reactants with each other. Solutions were destabilized and oils formed in the presence of A1 powder. Catalyst composition and concentration were determined by elemental analysis after aqueous extraction. The amount of A1C13 complexed to CoClz was determined by NMR ~pectroscopy.~

Butadiene Polymerization

Polymerizations were sometimes carried out in stirred flasks but more often in slightly pressurized and capped tubes or beverage bottles charged with benzene solutions or admixtures with catalyst components and &7


wt.-% butadiene according to a procedure developed in these laboratories.6 A catalytic oil or solution was generally transferred to the beverage bottle by means of a hypodermic syringe. Solids used to generate catalytic complex in situ were added in a dry state. There was no preferred order of charging ingredients, except that when thiophene was used to promote cis polymerization the procedure was such that monomer was not contacted with aluminum halide in the absence of thiophene, and the cobalt-aluminum halide complex was not exposed to thiophene for more than a few seconds in the absence of monomer in order to avoid precipitation and deactivation of the catalyst. The total amount of complexed and uncomplexed AICb, added in the form of one of the aforementioned solid or liquid compositions, ranged from 6 to 48 mmole/l. of benzene. The Co content ranged from 4 ppm to 24 mmole/l. Tubes and bottles were tumbled in polymerization baths a t temperatures in the range of 5-50°C. Polymerization times ranged from a few minutes to several days. Poly- merizations were stopped and rubber solutions protected against gelation by addition of 2-10 ml. tetrahydrofuran. After adding antioxidant the polymers were isolated by precipitation in methanol. Polymers were vacuumdried at 55OC. Structures of the polymers were determined (by a procedure similar to that described by Silas, Yaks, and Thornton') from infrared spectra. Molecular weights of the polymers were derived from the relation [ q ] = KM" in which the constant K and a were found by J. A. Yanko of these laboratories to be 3.24 X and 0.57, respectively, based on osmotic pressure measurements. M is the molecular weight, and [ q ] is the inherent visocisty of a toluene solution of polymer at 25OC. [q] is defined as [ q ] = 2.3 log qJC, in which q, is the viscosity of polymer solution relative to that of solvent and C is the concentration of the polymer solution (0.1 g./lOO ml.).

RESULTS

Catalytic Solutions

The magnetic resonance studies reported in the following paper4 indicated these catalytic solutions to contain varying relative amounts of dimeric AIC1, and a catalytically much more active green complex in which C O + ~ is coordinated in a square planar configuration to two A1C14- tetrahedrons, as discussed in more detail in the next section. These solutions were always found to contain both of these components regardless of whether the solutions were prepared by benzene extraction of pure or impure blue solid C O ( A ~ C ~ ~ ) ~ complex in which C O + ~ is coordinated to AIC14- in a octahedral configuration, or whether these solutions were obtained by the reaction of CoClz with A1C& in the presence of benzene or toluene. (The structural differences between the blue and green Co (AlCl& complexes in the solid and dissolved states, respectively, are discussed in detail in the following paper.4) The effects of preparative variables were not studied extensively, in part because one of the variables,


particle sizes and thus exposed surface areas of the solids used to prepare the solutions, was not readily reproducible, but in general it appeared that temperature had the greatest effect. The Co and A1 contents of solutions increased with higher temperatures, and the most active catalyst solutions were obtained by an overnight reaction at 8OoC. Table I shows some typical results obtained from solutions prepared overnight a t different temperatures, but cooled to room temperature before analysis.

TABLE I

Temp., "C. AlCll concn., mole/l. AI/Co

50 0.0220 4.0 80 0.1075 3 . 3

Catalytic Oils

The AlZ2 NMR spectrum of an oil which had been heated for 6 hr. revealed no evidence to indicate that arylation of complexed or uncomplexed A1CL had occurred, although the presence of significant amounts of arylated or partially arylated AIz7 cannot be ruled out due to excessive broadening of the resonance lines of such species because of the high viscosity of the oils. No attempt was made to determine elemental composition since different relative amounts of CoCh and AlCI, would dissolve to form oils, and aromatic hydrocarbon could be partially removed under vacuum without loss of catalytic activity.

A continuous evolution of hydrogen halide at an apparently steady rate occurred on heating or refluxing these oils in the absence of A1 powder. Analysis of water absorbed gas revealed the amount of hydrogen halide evolved in about 6 hr. to be no more than a trace compared to the total amount of halide present in the reaction mixture. The hydrogen halide corresponding to the halide of A1 in AlCh(Br3)-CoBrz(Clz) mixtures pre- dominated in the evolved gas. The amount of heating or gas evolved had no apparent effect on the catalytic activity of an oil provided it had been treated with A1 powder, and an oil could be used for polymerizations as soon as it formed and this could occur within a few minutes of contacting the reactants with each other. The addition of A1 powder retarded hydrogen halide evolution considerably and when the rate of reflux was kept to a minimum the hydrogen halide was barely detectable.

Polymerization

Although the catalytic oils were found to be insoluble in benzene, the further addition of butadiene produced immediate solution and polymerization within a few minutes to several hours. Oils prepared in the absence of powdered aluminum yielded resinous powders having virtually none of the less-than-theoretical unsaturation in the cis configuration, i.e., products similar to those obtainable by conventional cationic cataly-


S ~ S . ~ , ~ In the remaining text we shall refer to such polymerizations, products and structures as being therefore of the “cationic” type, in contrast with the more stereoregular varieties which we shall refer to as being of the “cis” type. Polymers having at least 94% cis content were obtained when the oil was prepared in the presence of about 1 wt.-% of aluminum powder based on the total amount of catalyst. To obtain cis polymers it was not necessary to have aluminum powder present during polymerization. No aluminum was required in the catalyst preparation or in the polymerization if thiophene was added just before polymerization was initiated. Effective polymerizations resulted from using 2 4 ml. oil/l. benzene. The stereoregularity of a polymerization with any of the forms of catalyst complexes described herein could be assured by using at least 200-300 mole-% thiophene based on soluble A1 content. In general, the molecular weights of most of the cis polymers prepared in the course of this investigation ranged from about 100,00(t200,000 and within the lower and higher limits described in the experimental section, the employ- ment of low temperatures, high A1 levels and low Co levels would tend to favor the production of molecular weights on the high side of this range. High temperatures, high Co and high A1 levels favored more rapid conversion to polymer. The amount of thiophene present over the minimum requirements for stereoregular polymerization had very little effect on molecular weight and other polymerization variables, and molecular weight reductions were barely observable until about a 2000 mole-% level based on soluble A1 content was reached. Generally, in a cis polymerization, the conditions affecting molecular weight would also affect the cis content in the same direction, but not nearly to same extent, with the changes amounting to no more than a few per cent at most. In addition to the previously noted effects of the Co level on the polymerization, there is one which is perhaps the most notable. To appreciate this, the specific effects of the other catalyst components should be noted first. AICl,, by itself, caused a typical cationic polymerization. The further inclusion of thiophene kinetically retardeds but did not appear to ther- modynamically shortstop or otherwise affect this cationic polymerization in any significant way. However, the further inclusion of as little as 4 ppm of Co,* or amounts known to be less, but not measured accurately, changed the course of the polymerization to such an extent that a quantitative yield of cis polymer was obtainable. This result is all the more remarkable in view of the tremendously large excess AIC1, relative to Co-A1 complex present under these conditions.

In the absence of thiophene, polymerizations of butadiene catalyzed by dilute CoC12-AlCla solutions in benzene resulted in sticky semiliquid

* The introduction of such small amounts of Co waa readily accomplished in several ways: small amounts of CoCl1-AlC13 solutions were combined with relatively large amounts of benzene solutions of AlC130r, instead, small amounts of any form of soluble Co could be added to Mcl3 solutions, aa under these conditions the amount of Co gegenions or other foreign species introduced thereby is insignificant.

3240 SCOTT, FROST, BELT, O'REILLY

10

0

polymers with a fairly high phenyl content. Generally, phenylation of the polymers was too severe to permit reliable determinations of structure from infrared spectra, but for some polymers having lower degrees of phenylation, 48-560/, of the total unsaturation was indicated to be in the cis configuration. Similar products resulted from polymerizations carried out in accordance with procedures described in reportss claiming the preparation of high molecular weight polybutadiene with a very high

-

Fig. 1. The effects of thiophene to catalyst ratios on conversion and cis content in a 7-hr. polymerization of butadiene in benzene at 30°C.: (a) estimated value derived from instances in which obscuring phenylation waa least extensive; ( b ) some phenylation; (c) no phenylation. Polymerizations performed in solutions containing 0.0151M AICla, 0.0039M CoCh, and 6.7 wt.-% butadiene.

cis content by using benzene solutions of sublimed aluminum halides and anhydrous cobalt halides. A study of the effects of various aliphatic and aromatic amines, ethers and sulfides indicated thiophene to be most effective as a suppressant of the nonstereoregular activity of these catalyst solutions. The effects caused by the introduction of increasing amounts of thiophene on the cis content of a polymer and the conversion to polymer in polymerizations catalyzed by a CoC12-A1C13 solution in benzene are indicated by the representative results shown in Figure 1.

STEREOREGUIAR DIENE POLYMERIZATION. I 3241

Solutions containing different amounts of catalyst components yielded results that were very similar to those shown but some variability, which did not affect the trends indicated, was noted. These variations probably resulted from differences in impurity levels and Co/A1 ratios which can be expected to reflect the different reactivities with respect to thiophene of uncomplexed AlCl, and AICl, complexed to Co even though the former is considerably more inert than the latter.4 The minimum catalyst concentration requirements, other than those already indicated, appear to depend to some extent on the general impurity level, including that which arises from the moisture and, perhaps, oxygen which remain adsorbed on the walls of the glass containers even after being over-baked and nitrogen- cooled. Generally, the larger a container a polymerization necessitated, the lower the minimum catalyst requirements turned out to be, probably as a result of the more favorable surface to volume relationship involved. A common procedure was to polymerize a solution of 6 wt.-% butadiene in 100 ml. benzene in a 6-0s. beverage bottle, and this would require the total concentration of complexed and uncomplexed to be at least 0.011M for effective cis polymerization to occur if the catalyst solution was prepared at 5OOC. However, if the catalyst was prepared at 8OoC., and as pointed out earlier, a larger part of the AlC13 present was complexed, the minimum effective A1 concentration was reduced to about 0.007- 0.008M. On a quart scale the minimum A1 concentration requirements were somewhat lower, and they could be reduced further by precooling the butadiene to -25OC. which freezes out a considerable portion of its moisture content. As a result of the low solubility of A1CI3 in benzene, relatively large volumes of catalyst solutions were often required, but this handling problem could be minimized by using much more soluble AlBr3 instead, or by increasing the solubility of AlCl, by complexing all or part of it with catalytically inert materials such as PbClz or alkali metal halides. 4, lo Polymerization results obtained with catalysts modified in this way did not differ significantly from those described for AlCl,, except to the extent that some of these systems led to somewhat lower A1 concentration requirements as the increased availability of AlCh- ions facilitated the formation and thereby increased the concentration of A1-Co complex relative to that of the catalytically more inert AlzCls in the catalyst solution. A solid blue form of the complex served as an effective cis directing catalyst only if at least part of it was allowed to pass into solution to form the active complex by including an aromatic hydrocarbon solvent in the polymerization recipe. The green liquid extract always contained uncomplexed AlCl,, regardless of whether the solid contained free AlCh. CoClz remained as an insoluble residue when solid complex of CoClz was Soxhlet-extracted with benzene. These effects probably arise from solution causing a disruption of the three-dimensional coordination about C O + ~ in the solid complex4t5 and, possibly, because the equilibrium of the dissociation reaction of the soluble complex lies somewhat to the right. Although there is little or no interaction between the un-


complexed AlC13 and butadiene or thiophene under cis polymerization conditi~ns,~ it is believed, nevertheless, that A1C13 serves a useful function in cis polymerization by deactivating impurities, either by direct interaction with the impurities or by replacing complexed AIC13 which impurities have caused to be deactivated. This is indicated by the finding that increasing the A1 concentration favors a high conversion and a high cis content.

The sulfur content (0.038, 0.044y0, determined by a procedure described by Wickbold”) of a high cis polymer prepared in the presence of thiophene and thoroughly Soxhlet-extracted with methanol was found to be in reasonable agreement with that expected (0.035y0) if there was one sulfur atom per polymer molecule with a molecular weight of 90,500 as derived from the inherent solution viscosity (2.16).

Most of the high cis polybutadienes prepared with cobalt-aluminum halide catalysts contained almost no toluene-insoluble gel. Some of these polymers had a cis content of 99%, but usually this content ranged from 96 to 98%. The trans-l14-configuration usually accounted for about twice as much of the remaining unsaturation as that attributed to 1,2- double bonds. Isoprene polymerized under similar conditions gave a polymer which by a less highly developed method of infrared analysis is estimated to have 8045% of its unsaturation in the cis configuration.

DISCUSSION

There is ample evidence to indicate that the interaction between CoClz and AlCl, involves the formation of a ~ornplex.~ Earlier electrical con- ductivity investigations12 suggested complex formation to occur between CoBrz and A1Br3. The volatilization of C O + ~ in sealed tube reactions of COCIZ and A1C13 at temperatures about 400-500OC. below the melting point of CoC12 and the solution of otherwise insoluble CoClZ in benzene in the presence of AlC13 could have come about only as a result of complex formation. The presence of CoC12-2AlC13 complex in the fusion and other solid products is indicated by x-ray diffraction data.4,6 Details of a magnetic resonance study of the structure of the active complex in solution and the changes produced by the interaction with thiophene and butadiene appear in the following paper.4 It is instructive, however, to examine the mechanistic implications of the results of that investigation and to consider their significance with respect to the results obtained under actual polymerization conditions.

Catalytic solutions of AlC& and CoClZ in benzene exhibit two separate APNMR signals. One arises from “uncomplexed” AlC13 and the other, which is shifted by 316 ppm to higher magnetic field, is due to tetrahedral AlC1,- complexed with CO+~. The high field absorption is interpreted4 as arising from the magnetic anisotropy of C O + ~ in an approximately square planar configuration. The concentrations of complexed A1C14- and Co +2


indicate the stoichiometry of dissolved complex to be CO(A~CL)~. the dissolved complex is believed to have the structure I :

Thus,

CI

On addition of thiophene or butadiene, the A121 NMR absorption of “uncomplexed” A1C13 remains virtually unaffected, thereby demonstrating the inert character of A1Cl3 under polymerization conditions. The complexed AlCld-, however, undergoes chemical reaction, as evidenced by the shift of its AlZ7 NMR signal to lower field and a decrease in intensity of the resonance line. It is unlikely that either thiophene or butadiene become attached to Co as a result of this interaction since any kind of attachment, e.g., via sigma or pi bonding, probably would cause a much more drastic ligand field effect on the C O + ~ EPR spectrum (a reduction in the number of unpaired electrons will occur if the added ligands provide a sufficiently strong crystal field at Co) than was ~bserved.~ As there is only one alter- native site at which such a reaction could occur, it is concluded that butadiene and thiophene become attached to the aluminum of complex I in the course of the initial interaction. Furthermore, it can be concluded that this reaction involves the displacement of terminal chlorine atoms as chloride ions since tetrahedral AlC14- does not have unoccupied positions at which reaction could occur, no configurations other than tetrahedral A1 were detected, and it is unlikely that cleavage of the A1-C1-Co-C1 ring occurs

as the spectroscopic evidence indicates the Al/Co ratios to remain sub- stantially the same in the original catalyst sqlution, the soluble reacting phase, and the less soluble product phase. The disposition of the displaced chloride ions and change in symmetry of the configuration about. the Cof2 can be accounted for by the following considerations. It can be surmised that Co+2 acquires a square pyramidal or an octahedral configuration as a result of the interaction with thiophene and/or butadiene because (a) C O + ~ does not retain its square planar configuration since this configuration produces an A12’ NMR absorption shift to higher field and as this absorption disappears in the course of the reaction the resonance shift also diminishes, (b) it is unlikely that a tetrahedral configuration about C O + ~ results since the modification of the EPR spectrum which would thereby result would be expected to be different from that observed14 and ( 6 ) since other configurations about Co +2 are not normally encountered there are no reasonable alternatives.* Furthermore, it is reasonable to

* The configuration about C O + ~ in this instance is deduced in the manner described because a direct detection by EPR spectroscopy is complicated to some extent by side effects arising from the solidification of the sample at the low temperature required for the observation of res~nance.~


conclude that C O + ~ becomes square pyramidal or octahedral by accepting the chloride ions displaced from Al, since in the spectroscopic investigation4 no reactions were detected which, conceivably, could also provide the additional ligands required for these configurations, e.g., reactions such as other structural rearrangements, or the aforementioned ring cleavage, or the addition of thiophene or butadiene or solvent to Co. Whether a square pyramidal or octahedral configuration results would depend on whether one or two chloride ions are transferred from A1 to Co. It should also be noted that since the spectroscopic study4 indicated no other structural changes to occur the complex I is not likely to be more than bifunctional in its reactions with butadiene and thiophene under polymerization conditions.

Since effective cis polymerization requires the addition of thiophene to precede the addition of butadiene, it appears that a t least one thiophene molecule reacts with complex I before butadiene does, and before significant cis polymerization can begin. If butadiene is not added at this point and two molecules of thiophene, or one molecule of thiophene in a bifunctional* capacity, are allowed to react with bifunctional complex I, no functional capacity remains for further reaction of complex with butadiene. The resulting product can be expected to be ineffective for the polymerization of butadiene, and this expectation was verified experi- mentally. Thus, since it is not likely that the active species for the initiation of cis polymerization is a 1 : 0 or a 1 : 2 2 catalyst to thiophene adduct, it can be concluded that the active species is the 1 : 1 adduct 11. To resolve the question about which one of the terminal Al-C1 bonds is likely to constitute the remaining reactive position of 11, it is constructive to consider how these bonds may be affected by the introduction of thiophene. Since the driving force for the first reaction between the complex and thiophene to form the adduct I1 must be the greater nucleophilicity of thiophene relative to chloride with respect to All a thiophene-, A1 -, C1 polarization relative to the original electron distribution in the terminal C1-A1-C1 bonds of the complex I can be expected to occur. The resulting destabilization of the A1-C1 bond in the thiophene-Al-C1 end of the adduct I1 would cause this chlorine atom to be displaced as chloride ion more readily than either of the chlorine atoms of the C1-Al-C1 group at the other end of the adduct. Therefore, the remaining functional position of the adduct I1 is expected to involve the A1-C1 bond adjoining the Al- thiophene linkage, provided steric requirements are favorable. No serious steric hindrance can be envisioned for the introduction of a butadiene molecule a t this point, and it is suggested that this reaction con- stitutes the initiation of the polymerization of butadiene, as shown in

Thiophene is considered to be bonded to A1 at its 2-position since this position is considered to be the most susceptible to electrophilic attack.13

eq. (1).


I

m

It is likely that thiophene provides the electron@) for sigma bonding* to A1 by the 3d orbitals of sulfur participating in the T delocalization around the ring,t since the availability of d orbitals is intimately involved in the chemistry of sulfur compounds16 and of thiophene in parti~ular. '~ Since the displacement of two chloride ions from A1 to Co represents consumption of the bifunctional capacity of the inorganic component of 111, it is evident that the next reaction of 111 should involve its organic component. Since electrophilic A1 can be expected" to induce local

* It is considered likely that mostly sigma bonding is involved since the susceptibility of thiophene to attack by protons and other electrophiles as well as the significant chemical stability of the producta of such reactions are indicative of the relatively high basicity of thiophene compared to most aromatic hydrocarbons, and sigma bonding in adducts of aromatic hydrocarbons with strong Lewis acids has been found to become more pronounced with increasing basicity of the hydrocarbon.14

t A recent discuasion of the relative insignificance of the sigma electron system in affecting the reactivity of conjugated molecules is given by Fukui et a1.ls


dipoles* within the attached thiophene and butadiene and ensuing reactions are likely to involve stabilization of the resulting polarized sites, it is constructive to qualitatively consider and compare the relative in- stability of these sites and the feasible reactions which might lead to their stabilization. In view of the chemical stability of sulfonium ions it is reasonable to believe that this part of the coordinated thiophene remains relatively inert. However, thiophene, coordinated in this manner, appears to have a residual nucleophilic capacity as the NMR evidence4 indicates that thiophene/2Al products form when reactions between thiophene and I are allowed to go to completion. Since the a-carbon of thiophene nearest to electrophilic A1 can be expected to be the most anionically polarized, it can be considered to be the one most likely to undergo a reaction with an electrophile such as a carbonium ion. Reaction with another A1 is likely to involve the carbon atom at the 5-position of thiophene. With regard to the potential reactions which the polarized butadiene component of I11 could undergo, it does not seem probable that a reaction involving the combination of the oppositely polarized ends of this component occurs, since in the course of numerous polymerizations involving this type of catalyst there never were any indications that cyclobutene, the product of such a reaction, might be present. There is also no reason to believe that the anionic end of the polarized butadiene would be capable of alkylating free butadiene in solution since the alkyl group of an alkyl aluminum compound is knownlg not to alkylatet butadiene. However, the cationic end of the polarized butadiene might be expected to have enough electrophilic character for it to be the most unstable and reactive site in 111, especially since it is not stabilized by the presence of a gegenion and such sites are generally believed to be generated and involved in conventional cationic polymerizations. Two courses of reaction involving this cationic site would appear to be available: (1) this site could react with a free butadiene molecule in solution, or (2) it could alkylate the thiophene component of I11 a t the anionically polarized carbon atom via a six- membered cyclic transition state. It is not likely that reaction I occurs to a significant extent since it is essentially equivalent to the reaction following initiation of a conventional cationic polymerization which upon continued reaction with more butadiene leads to a polymer with a nonstereoregular

* Studies of the effects of coordination on the reactivity of aromatic ligands indicate that a model of the bonding can best be represented by a polarization of the ligand without building up formal charges.x8

t An alkylation of this type may occur more readily in the polymerization of dienes or olefins With a different type of catalyst, such as those of the Ziegler type, since in those cases the Ti or V catalyst components, unlike Co+2 in our catalyst, have vacant 3dz2 and/or 3d&2 orbitals which would allow the diene to coordinate to these metal ions via d7r2-p7r bonding and the resulting increased electrophilicity of the coordinated diene would tend to facilitate alkylation. Another factor which might promote alkylation in these cases is that the alkylating group may have been transferred from A1 to the transition metal prior to diene or olefin alkylation and, iF this should be the case, the alkylation of the diene would not involve an Al-C bond, and a comparison with the situation under consideration would not apply.

STEREOREGULAR DIENE POLYMERIZATION, I 3247

structure. On the other hand, whereas reaction 1 is an intermolecular reaction, reaction 2 is an intramolecular reaction, and thus reaction 2 would tend to be favored kinetically. The much greater susceptibility of thiophene to electrophilic attack compared to that of free butadiene in solution, as is evidenced by the fact that a comparatively minute amount of thiophene can retard the cationic polymerization of butadiene, could be expected to be a cooperative factor favoring reaction 2. Furthermore, the susceptibility of thiophene to electrophilic attack is likely to be en- hanced by the polarization arising from the coordination of thiophene to Al. The vacancy created by the departure of thiophene from A1 as a result of reaction 2 would provide an electrophilic site on A1 to which another butadiene molecule could attach itself to set the stage for monomer to be fed into a polymer chain in the c is configuration by a propagating sequence of cycloalkylation reactions as shown in eqs. (2) and (3), where BD denotes butadiene.

BD --t

m m I -t C\ ,C-T (HI

C

Termination could occur as follows:

/

+ 2A'

\ -t A l - ( c i s BD),-T ( H I

/

BD= BUTADIENE


-cis BD-BD+ -cis BD- BD-BD+

CYCLOALKYLATION NO LONGER POSSIBLE

t

P

I J OPPORTUNITY FOR CYCLOALKYLATION

REMAINS m BD=BUTADlENE

\\.. etc

Cl I

-ep+ -BD-BD+ -BD-BD-BO+

* -cis BD-BD+

\ CYCLO \ /

CYCLO 1 ALKYLATION 1

BD

Fig. 2. Propagation reactions in the absence of thiophene.

This mechanism requires that the thiophene hydrogen not depart as a proton until appreciable cis polymerization has occurred. That this part of the mechanism is reasonable is indicated by previous reportss of the effects of thiophene on cationic polymerization. Additional evidence for the occurrence of cycloalkylation reaction 2 and against that of reaction 1 is provided by combining the implications of the findings that thiophene participates in the polymerizadion to the extent of one molecule per polymer


molecule and that for it to have stereospecific effect on the polymerization it has to be present before butadiene is added and polymerization is initiated. Since in this scheme the cis configuration of the polymer arises from propagation by a cycloalkylation reaction, another point in favor of this mechanism is that it discounts the importance of the configuration of the unbound monomer in the presentation to the catalyst. This point merits consideration when largely transoid monomers are involved, even though this configuration is favored by only about 3 kcal. in the case of butadiene.

The proposed mechanism could also account for the partial stereoregularity in the absence of thiophene and other findings shown in Figure 1. Basically, this mechanism suggests that for cis propagation to occur, the A1 of the complex I should have attached to it two groups, a t least one of which should be a polarized diene molecule, while the other can be another group possessing a nucleophilic site adjacent to A1 which permits this group to be transferred to the electrophilic end of the polarized diene via a cyclic transition state. This requirement is satisfied at the initiation stage under polymerization conditions in which thiophene is allowed to attach itself to all of the available catalytic A1 before butadiene becomes attached and cis polymerization can begin as soon as the first butadiene molecule attaches itself to the A1 of 11. However, in the absence of thiophene at this stage, the first butadiene molecule to attach itself to A1 cannot undergo the cycloalkylation reaction. Before it can undergo further reaction it has to await the approach of another butadiene molecule. As the second and subsequent butadiene molecules approach the catalyst- butadiene adduct they would have the choice of attaching either to the remaining available position of A1 in I or to the cationic end of the already attached butadiene. This choice would permit several reactions to occur concurrently, and some of the more significant types are shown in Figure 2.

Since the complex I by itself, in the absence of thiophene, gives rise to partial stereospecificity, it appears that the equilibrium of the reaction : thiophene + complex I 1 : 1 adduct 11, lies even more to the left* than is indicated by the excess thiophene required (c.f. Fig. 1: molar ratio of thiophene to adduct I is ca. 4.5) to bring about a sufficient concentration of the adduct I1 relative to complex I to have the stereospecific catalytic activity of adduct I1 dominate the course of the polymerization. Since this equilibrium favors the reactants and the reaction of I with thiophene to form I1 is likely to make I1 less electrophilic and a weaker competitor for reaction with butadiene than I, the course of the polymerization at low thiophene levels should reflect to a greater extent the activity of the separate catalyst components, complex I and thiophene, than that of their adduct 11. Thus a t very low thiophene levels, we might expect I to polymerize butadiene to form intermediates such as VI, the chain length

* The equilibria of similar reactions of several aromatic hydrocarbons with aluminum or titanium halides have been reported to lie far to the left.21


of which would depend on how soon thiophene can react with the cationic ends of the chains to stop the cationic propagation, and this would depend on the thiophene concentration. The m and n values of intermediates such as VI should decrease on raising the thiophene concentration gradually from a very low level. The resulting conversion should reflect the de- creasing molecular weight of VI, but since the reaction with thiophene should not interrupt the stereoregular propagation by cycloalkylation of intermediates such as V the contribution of this propagation should not only be reflected in the maintenance of a minimum conversion but also give rise to an increasing cis content of the product as the structural contribution of the non-stereospecific polymer component is lessened. Upon raising the thiophene level further, the m and n values of intermediates such as VI should eventually reduce to m = 1 and n = 0 or m = 0 and n = 0 to produce the intermediates IV or 11, respectively. Since the intermediates I1 and IV appear in the early stages of the cis polymerization according to the proposed mechanism and all of the catalyst now becomes converted to an exclusively cis-directing form, an enhance- ment of the cis polymerization should occur from this point on. Thus, the proposed mechanism of polymerization is in reasonable qualitative agreement with the observed effects of thiophene concentration on conversion and cis content.

For the aforementioned catalytic reaction conditions to prevail the addition of butadiene has to immediately follow that of thiophene to prevent the reaction of I with thiophene from proceeding to the point of significant precipitation of an insoluble reaction product. Such a precipitation is catalytically unfavorable for several reasons. The NMR study4 indicates that under such conditions thiophene acts in a bifunctional capacity as each thiophene molecule added was found to prevent two AlZ7 nuclei from contributing to the Co-A1 complex resonance. Thus, precipitation not only removes Co-A1 complex from solution, but it also involves consumption of the remaining functional capacity of 11, thereby causing it to be deactivated as a diene polymerization catalyst. With regard to the foregoing discussion of the formation of 11, it should also be noted that the NMR study4 of the interaction of I with thiophene was limited to those conditions under which precipitation occurs owing to the time required to scan a spectrum. Thus, it is reasonable that no effects reflecting an unfavorable equilibrium involved in the formation of I1 were observed in that study since this reaction would be driven to completion by a subsequent consumption of I1 to yield an insoluble product.

Although no attempts were made to determine the structure of this insoluble and catalytically inactive product, there are some observations and considerations which suggest it to have the structure shown (VII). Spectroscopic investigation4 indicated both I and thiophene to be acting in bifunctional capacities and that, except for the chloride transfer from A1 to Co, the identity of the inorganic complex remains intact throughout the course of reaction of I with thiophene. That this reaction involves a


pn:

polymerization is suggested by its physical resemblance to a typical condensation polymerization in that when the reaction is carried out with the oily phase of a concentrated solution of the reactants this phase becomes progressively more viscous until a thermoplastic resin results. The reasons for proposing the polymer structure indicated are that, as discussed earlier, further reaction of the thiophene component of I1 can be expected to involve the 5-position in a reaction such as this, and the second site of reaction of the I component of I1 can be expected to reside at the thiophene-free-end of I1 despite the destabilization of the A1-C1 bond adjacent to the first Al-thiophene bond to form, since adjacent displacement would result in a product having two large and similarly polarized groups attached to the same A1 atom, and steric hindrance aggravated by electrostatic repulsion would tend to be pronounced.

As indicated earlier, catalytic oils prepared in the presence of a trace of aluminum powder can catalyze a cis polymerization of butadiene in the absence of thiophene. However, thiophene is still required in the cis polymerization of isoprene and in any case if aluminum powder is not used in the catalyst preparation. There are several reasons for believing that the functions of aluminum powder and thiophene are related to the proton concentration in these systems. Since similar oils derived from aluminum halides and aromatic solvents appear to involve 1 : l complexes of these components,21~22 it is reasonable to believe that our oils also involve 1 : 1 adducts of the complex I and aromatic solvent with the latter component serving the same function in cis polymerizations as thiophene in its adduct 11. If effective cis polymerization is to occur the opportunity for cationic polymerization to compete has to be minimized, and as protons can initiate a cationic polymerization the prevailing conditions would have to be such that their concentration or activity is minimized. When thiophene reacts with the complex I to form adduct I1 the system is provided with a built-in proton deactivator as the stability of the thiophenium ion that results tends to delay the departure of a proton8 until appreciable cis polymerization has occurred, whereas in an adduct of I with an aromatic solvent the cationic charge on the aromatic component of this adduct would not be stabilized to that extent and the adduct would tend to stabilize itself


by releasing a proton. This release of protons becomes observable at reflux temperatures when these protons are evolved in the form of hydrogen halide. When aluminum powder is added, the lowering of the proton concentration which may occur by heterogeneous reduction of H + by aluminum appears to be sufficient to prevent cationic polymerization from competing effectively in the case of butadiene, but not when isoprene is the monomer. These results reflect the greater susceptibility of isoprene to cationic polymerization as indicated by the faster cationic polymerization3 of isoprene compared to that of butadiene. The proton concentration in the absence of thiophene and aluminum powder is probably controlled by the equilibria involved in the interaction of catalyst with solvent, e.g., I + ArH * I&+ (H) + I-& + H+, and this would account for the observation that under these conditions a cationic polymerization always occurs, regardless of extent of hydrogen halide contamination of the catalyst components before they were added to solvent. With regard to other possible functions of aluminum powder in the preparation of catalyst, it does not seem reasonable that aluminum powder causes cis polymerization by facilitating arylation of catalytic species such as I by removing hydrogen halide from this reaction. If such a reaction occurs, it must be exceedingly slow, for even after many hours of refluxing the aluminum consumpt.ion was still too small to be detectable, and secondly, even though in the absence of aluminum powder the hydrogen halide evolution was very small compared to the total amount of halide present, the addition of aluminum powder merely reduced but did not completely suppress this evolution. Since oils, formed within a few minutes of bringing the reactants together, were effective for cis polymerization the amount of arylation facilitated by the presence of aluminum, if it does occur, could hardly have been significant enough within this time interval for it to be responsible for cis polymerization. Similarly, since heterogeneous reduction of H -I- by aluminum metal is also likely to be a very slow reaction, it would seem more probable that a lowering of the proton concentration is caused by a physical, and perhaps chemical, adsorption of protons on the aluminum oxide surface of aluminum powder. Thiophene is an effective proton deactivator because the addition of Hf is a homogeneous reaction in this case.

The EPR evidence4 indicates a radical-cation of butadiene to form as a result of a Lewis acid-diene charge transfer type of reaction. However, the formation of such a radical-cation can not be considered to be a unique feature of stereoregular polymerization since a conventional type of nonstereospecific catalyst, such as SbCls, was also found4 to produce this radical-cation of butadiene. It is conceivable that this ion arises as a by- product of the main reaction of butadiene with a Lewis acid, since similar interactions of Lewis acids with other conjugated systems, such as aromatic hydrocarbons, have been reportedI4 to yield radical-cations of the latter to varying extents in addition to covalently bonded adducts, de-


pending on a combination of factors such as the basicity and oxidation potential of the hydrocarbon involved.

Monoolefins, such as 1-butene and 1-hexene, when contacted with a solution of catalyst complex, were found to give rise to a typical cationic type of polymerization which could be retarded by the presence of thiophene. The products appeared indistinguishable from those which can he obtained with similar solutions of aluminum chloride.

The catalytic activity of combinations of aluminum halides with other metal halides23 is still under investigation. Preliminary indications are that for other combinations which are effective a similar catalyst structure and polymerization mechanism are involved. However, it is not to be im- plied that details of the interactions and mechanism described here for the CoCl2 complex, such as the coordination symmetry of C O + ~ before and after chloride transfer, apply to all catalytic combinations. Some of the differences in activity of these complexes can be understood in terms of the modifying effects which the application of ligand field and molecular orbit theories would predict to occur.

The authors are indebted to their colleagues a t the B. F. Goodrich and Gulf Research Centers for their suggestions and helpful discussions, and to A. K. Kuder and Miss M. J. Ferguson of the B. F. Goodrich Research Center for their assistance in obtaining. analytical and infrared data.

References 1. Gaylord, N. G., and H. F. Mark, Linear and Stereoregular Addition Polymers:

Polymerization with Controlled Propagation, Interscience, New York, 1959, (a) pp. 168-186,500-506; (b) pp. 90-106,162-168.

2. Ferington, T. E., and A. V. Tobolsky, J. Polymer Sci., 31,25 (1958). 3. Richardson, W. S., Rubber Chem. Technol., 27,961 (1951). 4. O’Reilly, D. E., C. P. Poole, Jr., R. F. Belt, and H. Scott, J. Polymer Sci., A2, 3257

5. Belt, R. F., and H. Scott, forthcoming publication. 6. Harrison, S. A., and E. R. Meincke, Anal. Chem., 20.47 (1948). 7. Silas, R., J. Yates, and V. Thornton, Anal. Chem., 31,529 (1959). 8. Overberger, C. G., and G. F. Endres, J. Polymer Sci. 16,283 (1955). 9. Shell Oil Co.: Belg. Pat. 579,689 (June 15, 1959); Austral. Pat. 49,765 (June 12,

10. Kikets, V. A., Mem. Instit. Chem. Ukrain. Akad. Sci., 3, 489 (1936); Chem.

11. Wickbold, R., Angew. Chem., 69,530 (1957). 12. Isbekoff, B. A., and W. Plotnikoff, 2. Anorg. Chem., 71, 332 (1911); J . Russ.

13. Longuet-Higgins, H. C., Trans. Faraday Soc., 45,173 (1949). 14. Aaldersburg, I. J., C. I. Hoijtink, E. L. Mackor, and W. P. Weijland, J . Chem.

15. Fukui, K., H. Kato, T. Yonezawa, K. Morokuma, A. Imamura and C. Nagata,

16. Cilento, G., Chem. Revs., 60,147 (1960). 17. Fajans, K., 2. Electrochem., 34,502 (1928). 18. Jetton, R. L., and M. M. Jones, Znorg. Chem., 1,309 (1962). 19. Weber, H., Angezu. Chem., 72,274 (1960).

(1964).

1959).

Abstr., 31,7765 (1937).

Phys. Chem., 43.20 (1911).

SOC., 1959,3055.

Bull. C h a . Soc., Japan, 35,38 (1962).


20. Aston, J. G., G. Szasz, H. Woolley, and F. G. Brickwedde, J . Chena. Phys. , 14.67

21. Brown, H. C., and W. J. Wallare, J . Am. Cheni. SOC., 75 , 6225 (1953); B. Elliot,

22. Dilke, M. H., 1). D. Eley, and M. J. Perry, frlpscarch (I,ondon), 2,538 (1949). 23. Goodrich Gulf Chemicals, Inc., South African Pat. 61/’283 (January 18, 1961).

(1946).

A. G. Evans, and E. Dowen, J . Chem. Soc., 1962,689.

Resum6 On d6crit la polymerisation du 1-3 butadiene par plusieurs compositions catalytiquea

COC~Z-AIC~. Des produits solides bleus de la reaction de CoClz avec AlCl3, dans lesquels le Co eat eoordin6 en Configuration octahgdrique, sont inefficacea comme catalyseurs st6r6osp6cifiques1 8. moim qu’ils ne soient trait& par un hydrocarbun aromatique qui conduit 8. une solution d’un melange de eomplexe catalytique vert Co(A1Cl4)2, dans lequel la Coordination du Co a une configuration planaire carrbe, e t AlC& qui est comparative- ment inerte dans les conditions de polymerisation. Ce melange se forme independemment du rapport molaire resultant (et fr6quemment variable) de 1’Al e t du Co en solution, e t independemment du fait que lea produits solides contiennent AIC13 qui n’est pas complex6 avec le Co. Des solutions similaires r6sultent de la reaction de CoCl2 avec AlCb dans un hydrocarbure aromatique. En absence d’un modificateur une solution benz6nique d’un complexe Co(AlC14)2 catalyse les polym6risations st6r6or6gulibres e t non-stMor6gulibres b peu prbs dans une mbme &endue. Cependant l’addition de thiophene favorise la polymerisation cis au depend de la polymerisation non-ster6or6gulibre; on a obtenu un rendement quantitatif de polybutadiene avec 9699% de son insatura- tion dam la configuration cis et une teneur en soufre correspondant b un groupe thiophene terminal par molecule de polymbre. La teneur en cis et la conversion atteint un maximum 8. une teneur en thiophene de 300 moles en yo bas6 sur AlCla. A faible teneur en thiophbne, la conversion, contrairement b la teneur en cis, passe par un minimum avant d’atteindre un maximum. Les polymbres avec une teneur similaire, Blev6e en cis, sont aussi obtenus en absence de thiophbne en prepparant des compositions catalytiquea huileuses dans le toluene ou le xylbne en presence de traces d’aluminium, de poudre, de magnesium ou de zinc qui devraient servir principalement comme capteur de protons. On discute un mecanisme possible en accord avec les rksultats de polymerisation. On suggere que la polymerisation stkr6or6gulibre implique la fixation du thiophbne et du butadiene 8. un atome d’aluminium du complex Co(A1Cl4)2 dans lequel le Co est coordin6 dans une configuration planaire carree, par d6placement dea ions chlorures de cet atome d’aluminium vers des positions de coordination vacantes de l’atome de cobalt; il en r6sulte donc une configuration octahbdrique de l’atome du cobalt, suivie d’une reaction de cyclo-alkylation entre le thiophhne coordine et le butadiene et insertion subsequente du butadiene dans la chaine polymerique par une sequence de reactions similaires de cyclo-alkylation.

Zusammenfassung Die Polymerisation von 1,3-Butadien mit CoCl~-AlCl~-Katalysatoren verschiedener

Zusammensetzung wird beschrieben. Die blauen, festen Reaktionsprodukte von CoCL mit AlCL, in denen Co eine oktaedrisch koordinierte Konfiguration zeigt, sind als stereo- spezifische Katalysatoren wirkungslos, solange sie nicht mit einem aromatischen Kohlen- wasserstoff unter Bildung einer Losung der Mischung des grunen katalytischen Co- (A1C14)2 mit ebener, quadratischer Konfiguration der Co-Koordination und des bei Polymerisationsbedingungen relativ unwirksamem AlCla behandelt werden. Diese Mischung bildete sich ohne Rueksicht auf das resultierende (und oft variierende) Mol- verhiiltnis von Al zu Co in Losung und ohne Rucksicht darauf, ob die festen Produkte nicht mit Co komplexiertes AlC& enthalten. xhnliche Losungen bilden sich bei der Reaktion von CoC12 mit AlC1, in einem aromatischen Kohlenwasserstoff. In Abwesen-

STEREOREGULAR DIENE POLYMERIZATION. 1 3255

heit eines Modifikators katalysiert eine Losung dea Co(AlCl&-Komplexes in Beneol stereoregulare und nichtstereoregulare Polymerisation in ungefahr demselben Mass. Der Zusate von Thiophen jedoch begiinstigt (,"is-Polymerisation auf Kosten der nicht- stereoregularen Polymerisation; dabei wurde eine quantitative Ausbeute an Polybuta- dien mit Y4990/, seiner Ihppelbindungen in der ('is-Konfiguration und einem Schwefel- gehalt entsprechend einer Thiophenendgruppe pro Polymermolekiil auf diese Art erhalten. Cis-Gehalt und Umsatz erreichten bei einem Thiophengehalt von 300 Molyo bezogen auf AlCb ein Maximum. Bei niedrigerem Thiophengehalt geht der Umsatz im Gegensatz zum Cis-Gehalt durch ein Minimum, bevor er ein Maximum erreicht. Poly- mere mit einem ahnlich hohem Cis-gehalt wurden auch in Abwesenheit von Thiophen durch Darstellung einea olartigen Katalysatorgemisches in Toluol oder Xylol in Gegen- wart von Aluminium-, Magnesium- oder Zinkpulver erhalten, die hauptsachlich als Protonenfllnger zu dienen scheinen. Die Stereospeeifitat der katalytischen Losungen war im wesentlichen von dem Verhaltnis dea in Losung befindlichen Al und Co unab- hangig. Ein nioglicher Mechanismus zur Erklarung der Polymerisations-daten wird diskutiert. Es wird angenommen, dass die stereoregulare Polymerisation iiber die Bindung von Thiophen und Butadien an ein Aluminiumatom des Co(A1C14)t-Komplexes verlauft, in welchem Cobalt in einer quadratisch planaren Konfiguration koordiniert ist. Chloridionen werden von diesen Aluminiumatomen zu freien Koordinationstellen des Cobaltatoms verlagert, was zu einer oktaedrischen Konfiguration um das Cobalt fiihrt. Darauf folgt eine Zykloalkylisierungsreaktion ewischen dem koordinierten Thiophen und Butadien und eine Einschiebung von Butadien in die Polymerkette durch eine Folge ahnlicher Zykloalkylisierungsreaktionen.

Received May 27, 1963 Revised September 2, 1963

Documents

Stereoregular diene polymerization with inorganic catalysts. I. cis 1,4-Polymerization of 1,3-butadiene with a cobaltous chloride–aluminum chloride complex