Abstract:
Disclosed is a novel process for the hydrohalogenation of polybutadiene and butadiene-containing copolymers in the presence of aqueous hydrogen halides. The process permits the hydrohalogenation of from about 1 to about 50% of the carbon-carbon double bonds of the polybutadiene chain and includes the steps of dissolving the polymer in a suitable organic solvent containing a catalytic amount of a quaternary ammonium salt, adding an aqueous hydrogen halide, mixing the reactants and thereafter extracting the hydrohalogenated product.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the hydrohalogenation of polybutadiene and butadiene-containing copolymers via aqueous hydrogen halides. The addition of hydrogen halide gases to unsaturated polymers is generally known wherein hydrogen is added to one carbon of an olefinic group and the halogen is added to the other. 
     DESCRIPTION OF THE PRIOR ART 
     One U.S. patent of which we are aware, U.S. Pat. No. 2,596,878, discloses the hydrohalogenation of stabilized aqueous dispersions of natural rubber utilizing hydrogen halide gas. The stabilizers are employed to prevent coagulation of the latex upon addition of the hydrogen halide and include cationic soaps, cation active compounds and nonionic emulsifying agents. The patentee notes an advantage of his process over known prior art in that his does not require the use of rubber solvents which are not only themselves costly but also time-consuming to remove. Considering the structure of the natural rubber molecular, comprising the isoprene group, ##STR1## the reaction has long been understood to proceed by the addition of the halogen to the tertiary olefinic carbon with the hydrogen bonding to its mate as follows: ##STR2## 
     A British Pat. No. 922,373, exists which does disclose a process for the hydrochlorination of butadiene-containing polymers to produce products having chlorine contents of up to 28-30% by weight. The preferred reaction is conducted with dry hydrogen chlorine gas, acting upon the polymer composition in a suitable rubber solvent under a pressure of from 0-35 atmospheres and in the presence of from 0-100% of a Friedel-Crafts catalyst, e.g., SnCl 4 , TiCl 4 ,AlCl 3 , and the like. The patent reports the known, unsuccessful attempts to hydrochlorinate polybutadiene with hydrogen chlorine gas without a rubber solvent and with liquid hydrogen chlorine under any conditions. 
     Thus, a process for the direct hydrohalogenation of polybutadiene or butadiene-containing polymers with aqueous hydrogen halides is not known to us. Such a process would be useful inasmuch as the aqueous hydrogen halides are generally more conveniently employed than the gaseous form. Usefulness of the resulting halogenated polymers is presently well-known and need not be repeated herein. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a process for the hydrohalogenation of polybutadiene and butadiene-containing polymers to produce useful halogenated polymers. 
     It is another object of the present invention to provide a process for the hydrohalogenation of butadiene-containing polymers by the use of aqueous hydrogen halides. 
     It is yet another object of the present invention to provide a process for the hydrohalogenation of butadiene-containing polymers containing controlled amounts of halogen atoms in the chain, e.g., hydrohalogenation of up to 50% of the olefinic bonds. 
     It is still another object of the present invention to provide a process for the hydrohalogenation of butadiene-containing polymers utilizing the catalytic effect of quaternary ammonium compounds. 
     These and other objects of the present invention shall become apparent from the specification and claims which follows. 
     In general, a process for the hydrohalogenation of butadiene-containing polymers, hereinafter used to designate polybutadiene and butadiene copolymers, includes the steps of dissolving the butadiene-containing polymer in a suitable organic solvent in the presence of a catalytic amount of a quaternary ammonium salt, adding an aqueous hydrogen halide HX, wherein the X can be fluorine, chlorine, bromine or iodine and, mixing the reactants to form the hydrohalogenated product. After the reaction has been completed the desired product is extracted via conventional methods. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The butadiene-containing polymers which can be hydrohalogenated according to the process of the present invention include those which are generally copolymerizable therewith such as the monovinyl aromatics, e.g., styrene and acrylonitrile, as well as polybutadiene itself. Polymerization of the butadiene-containing polymer can be carried out in any convenient manner and does not form a part of the present invention. Similarly, number average molecular weight of the polymer, which can range from about 1,000 to 1,000,000, will be selected on the basis of the desired halogenated product. And, butadiene copolymers can have from 1 to about 99% by weight of polybutadiene. Generally, all that is necessary is that the polymer to be halogenated contain olefinic unsaturation. 
     After selection of the polymer has been made, it is then dissolved in a suitable solvent such as chlorobenzene. Alternatively, benzene, alkyl halides or alkylaromatic compounds could be employed. In order for the hydrohalogenation reaction to proceed, it is necessary to employ as a catalyst a quaternary ammonium compound. Compounds having the general formula (R 4  N)X, wherein the R is selected from the group consisting of alkyl groups having from 1 to about 20 carbon atoms, aryl groups having from 6 to about 12 carbon atoms and mixtures thereof, and X is a halogen selected from the group consisting of fluorine, chlorine, bromine and iodine, have been found to be satisfactory, with tetraethyl ammonium chloride being preferred. Other exemplary compounds which can be employed include tetramethyl ammonium bromide, tetraphenyl ammonium bromide, tetra-p-ethylphenyl ammonium bromide, phenyl trimethyl ammonium chloride and triphenyl ethyl ammonium bromide. It should be understood that selection of a particular catalyst can readily be made by those skilled in the art from the groups listed and that the disclosure provided herein is not to be construed as limiting. Amounts of the desired catalyst to be added are from about 2 to 70% by weight. 
     Hydrohalogenation is accomplished with a concentrated aqueous hydrogen halide HX wherein the X can be fluorine, chlorine, bromine or iodine. The concentrated acid is added to the reaction vessel containing dissolved polymer and catalyst and is thereafter mixed for a period of time of at least 48 hours. Temperature of the reaction vessel can be maintained between about 50° and 150° C. with 80° C. being preferred. Upon completion of the hydrohalogenation, the acid is neutralized with a suitable base and the product is recovered via suitable methods. 
     In the examples which follow, Duradene HX-510 (a copolymer of butadiene 77% by weight and styrene 23% by weight) and Diene-35 (polybutadiene) were hydrochlorinated according to the process of the present invention. (Duradene is a registered trademark of the Firestone Synthetic Rubber and Latex Co.) Examples 1-9 are presented in Table I, wherein Duradene HX-510 and Diene-35 were hydrochlorinated in the presence of different solvents and different catalysts. Reaction temperatures were maintained at 80° C. with the exception of example 7 (30° C). Reaction times were all 120 hours. Chlorine content, in terms of weight percent, dilute solution viscosity (DSV) determined in tetrahydrofuran (THF), percent gel, and color of the product for examples 1-9 are presented in Table II. Examples 10-16 are presented in Table III, wherein Duradene HX-510 and Diene-35 were hydrochlorinated in the presence of chlorobenzene and tetraethyl ammonium chloride (Et) 4  NCl. Here, the amounts of HCl and (Et) 4  NCl were varied as was the reaction time. Reaction temperature was maintained at 80° C. In Table IV, product characteristics for examples 10-16 are again reported and, in addition, the solubility in THF. It is to be understood that the examples are representative of the present invention and are intended to illustrate the results achieved in the practice of our invention. 
     Each of the examples 1-16 was run as follows unless otherwise noted in the Tables. In a reaction vessel containing 300 cc of the solvent and 3-6 gms of the quaternary ammonium salt approximately 9 gms of the butadiene polymer was dissolved. 100-300 cc of concentrated HCl was added as the aqueous hydrogen halide and the mixture was thereafer tumbled for 96-168 hours at 80° C. Extraction of the reaction product was begun first, by separation of the solvent layer, followed by its neutralization with ammonium hydroxide and lastly, its precipitation with methanol. 
     
                                           TABLE I__________________________________________________________________________      Example No.:Ingredients:      1   2   3   4   5   6   7   8   9__________________________________________________________________________Duradene (HX-150)gms.       9   9   9   9   9   9   9   9   --Diene - 35 gms.      --  --  --  --  --  --  --  --  9Conc. HCl cc.      300 300 300 300.sup.a                      300 300 300 300 300                  (1N)Chlorobenzene      300 300 300 300 300 300 300 --  300cc.Benzene, cc.      --  --  --  --  --  --  --  300 --CetyltrimethylNBr gms.   6   --  --  --  --  --  --  --  --(Et).sub.4 NBr gms.      --  6   --  --  --  --  --  --  --(Et).sub.4 NCl, gms.      --  --  6   6   12  30  6   6   6__________________________________________________________________________ .sup.a One Normal HCl used. 
    
     
                                           TABLE II__________________________________________________________________________      Example No.:      1   2   3   4   5   6   7   8   9__________________________________________________________________________Chlorine content% by wt.   4.26          4.11              5.13                  N.R.                      4.98                          4.34                              0.16                                  2.52                                      (b)                              (a)DSV (in THF)      1.73          1.38              1.73                  --  1.47                          1.75                              2.26                                  1.83                                      --Gel %      0.0 5.23              0.0 2.6 0.0 0.0 0.0 0.0 --Color of Product      Light          Dark              Brown                  --  Brown                          Brown                              Light                                  Light                                      Light      Brown                       Brown                                      Brown__________________________________________________________________________ (a) Reaction temperature 30° C. (b) Product obtained, accidentally destroyed prior to evaluation. 
    
     
                       TABLE III______________________________________     Example No.:Ingredients:       10     11     12   13   14   15   16______________________________________Duradene HX-510gms.        --     9      9    9    9    9    9Diene-35 gms.       9      --     --   --   --   --   --Chlorobenzenecc.         250    250    250  250  250  250  250Conc. HCl, cc.       200    200    200  200  100  100  100(Et).sub.4 NCl, gms.       3      3      3    6    3    3    6Reaction Time(hours)     96     96     168  96   96   168  168______________________________________ 
    
     
                                           TABLE IV__________________________________________________________________________     Example No.:     10  11  12  13  14  15  16__________________________________________________________________________Chlorine content% by wt.  1.60         3.64             4.40                 4.12                     2.00                         3.54                             2.80DSV (in THF)     1.61         1.78             1.85                 1.88                     1.49                         1.65                             1.57% gel(2 weeks old)     0.0 0.0 0.0 3.49                     1.05                         1.79                             2.13Color of Product     Light         Light             Light                 Light                     Brown                         Dark                             Light         Brown             Brown                 Brown   Brown                             BrownSolubility in THF     sol.         sol.             sol.Solubility in THFafter 2 months ofstorage   sl. sl. sol.     insol.         insol.__________________________________________________________________________ 
    
     From examples 1-3 in Table II, it can be seen that all three catalysts enabled the hydrochlorination reaction to proceed and, that reasonably high chlorine levels, for this process, were obtained. In example 4, the reaction did not take place because 1 normal HCl was utilized in lieu of the concentrated acid. Examples 5 and 6, indicated that increasing the amount of the tetraethyl ammonium chloride by factors of two and five did not effect the chlorine content. Example 7 had a very low chlorine content due to the lower reaction temperature of 30° C. Example 8 indicated that the solvent benzene worked, but yielded a lower chlorine content than chlorobenzene. Example 9 has not been reported because the product obtained was inadvertantly destroyed prior to evaluation. 
     From examples 10-12 in Table IV, it can be seen that lowering the amounts of HCl and tetraethyl ammonium chloride lowered the chlorine content of the resultant product, but did not otherwise effect the reaction. Chlorine content for example 10, the hydrochlorination of polybutadiene, was significantly lower than that found for the reactions of Duradene. In examples 13-16, the amounts of HCl were varied from 200 to 100 cc, the amount of catalyst was 3 to 6 gms. and the reaction time was increased from 4 days to 7. While hydrochlorination of all four products was obtained, gelling was also observed, after the work up to isolate and purify the product, making the products useless; for this reason solubilities were not attempted. 
     Addition of the hydrogen and chlorine, or other selected halogen, is made to the olefinic groups --C ═ C -- of the butadiene to yield the structure: ##STR3## Unlike the direct halogenation of these polymers, which would add a halogen atom to both sides of the double bond, or a process such as described in U.S. Pat. No. 2,596,878, which allows for the hydrohalogenation of substantially all of the double bonds, by employing the process set forth herein a milder, more controlled addition of halogen to the double bonds may be facilitated. Thus, the process is useful wherein up to about 50% of the available carbon-carbon double bonds of the polybutadiene chain are to be hydrohalogenated. 
     Thus, it can be seen that the disclosed invention carries out the objects of the invention set forth above. As will be apparent to those skilled in the art, the preceding examples can be varied by the selection of the various ingredients as well as the amounts thereof according to the foregoing specification, and it is believed that the preparation and use of these can be determined to achieve substantially the same results without departing from the spirit of the invention herein disclosed and described, the scope of the invention being limited solely by the scope of the attached claims.