Abstract:
The present invention relates to the polymerization and copolymerization of monomers in the presence of fluorinated propylene solvents. More particularly, the present invention relates to the use of polymerization mediums suitable to polymerize one or more monomers to form polymers and/or copolymers, with a tetrafluoropolypropylene being used as a solvent or diluent for the one or more monomers.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/724,293, filed on Nov. 8, 2012, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the polymerization and copolymerization of monomers in the presence of fluorinated propylene solvents. More particularly, the present invention relates to the use of polymerization mediums suitable to polymerize one or more monomers to form polymers and/or copolymers, with a tetrafluoropolypropylene being used as a solvent or diluent for the one or more monomers. 
     DESCRIPTION OF RELATED ART 
     Methyl chloride is commonly used as a solvent or diluent in the process of producing polyalpha-olefins such as polyisobutylene. For example, slurry polymerization processes in methyl chloride are used in the production of high molecular weight polyisobutylene and isobutylene-isoprene butyl rubber polymers. Likewise, polymerizations of isobutylene and para-methylstyrene are also conducted using methyl chloride. Similarly, star-branched butyl rubber is also produced using methyl chloride. 
     Typically, such polymerization processes use methyl chloride at low temperatures, generally at about −90° C., as the diluent for the reaction mixture. Methyl chloride is employed for a variety of reasons, including that it dissolves the monomers and the catalyst, e.g., aluminum chloride, but not the polymer product. 
     However, there are a number of problems associated with the polymerization in methyl chloride, for example, the tendency of the polymer particles in the reactor to agglomerate with each other and to collect on the reactor wall, heat transfer surfaces, impeller(s), and the agitator(s)/pump(s). The rate of agglomeration increases rapidly as reaction temperature rises. Agglomerated particles tend to adhere to and grow and plate-out on all surfaces they contact, such as reactor discharge lines, as well as any heat transfer equipment being used to remove the exothermic heat of polymerization, which is critical since low temperature reaction conditions must be maintained. 
     SUMMARY OF THE INVENTION 
     The present invention relates to polymerization mediums suitable to polymerize one or more monomers to form polymers and copolymers thereof, a fluorinated polypropylene being used as a solvent or diluent for the one or more monomers. The polymerization mediums are especially suitable for slurry polymerization processes. 
     In one aspect, a polymerization medium is provided that includes, consists essentially of, or consists of, one or more catalysts, a tetrafluoropropylene, and one or more monomers including at least one alpha-olefin. 
     In another aspect, a polymerization process is provided which uses such a polymerization medium in a reactor to produce polymers and/or copolymers. 
     In yet another aspect, a polymerization medium and process is provided which uses trans-1-chloro-3,3,3-trifluoropropene in place of a tetrafluoropropene as set forth above. 
    
    
     DETAILED DESCRIPTION 
     There is concern for the environment in terms of global warming and ozone depletion. Use of tetrafluoropropylenes in the present invention addresses such issues. For example, trans-1,3,3,3-tetrafluoroprop-1-ene (or “trans-HFO-1234ze”) has zero ozone depletion potential (ODP), and a global warming potential (GWP) of 6, which is quite low. 
     The toxicity and flammability of hydrofluorocarbons and hydrofluoro-olefins is also of potential concern. Hydrofluoro-olefins, in particular, are often toxic and flammable; however, tetrafluoropropylenes of the present invention also address this issue as well. For example, trans-HFO-1234ze is bath non-toxic and is not highly flammable. Additionally, trans-HFO-1234ze, can reduce the flammability of some monomers (e.g., isobutylene) when used in combination with those monomers. 
     Monomers which may be used in accordance with the present invention include monomers which can be polymerized using a Lewis acid dispersed in a diluent. Alpha-olefins, such as isopropylene, are especially preferred; however, any monomer which may be cationically polymerized (e.g., olefins, benzenes, styrenes, vinyl ethers, etc.) may also be used in accordance with the present invention. 
     Particularly preferred tetrafluoropropylenes include: trans-1,3,3,3-tetrafluoroprop-1-ene; cis-1,3,3,3-tetrafluoroprop-1-ene; 2,3,3,3-tetrafluoropropene; and mixtures thereof. In the alternative, trans-1-chloro-3,3,3-trifluoropropene may be used instead of tetrafluoropropylene, and achieve many of the same benefits as tetrafluoropropylenes. 
     Some tetrafluoropropylenes in accordance with the present invention can also be useful in that they can form compositions which are azeotropic or azeotrope-like. As used herein, the term “azeotropic or azeotrope-like” is intended in its broad sense to include both compositions that are strictly azeotropic and compositions that behave like azeotropic mixtures. From fundamental principles, the thermodynamic state of a fluid is defined by pressure, temperature, liquid composition, and vapor composition. An azeotropic mixture is a system of two or more components in which the liquid composition and vapor composition are equal at the stated pressure and temperature. In practice, this means that the components of an azeotropic mixture are constant-boiling and cannot be separated during a phase change. 
     Azeotropic compositions are constant boiling compositions, and azeotrope-like compositions are constant boiling or essentially constant boiling. In other words, for azeotropic and azeotrope-like compositions, the composition of the vapor formed during boiling or evaporation is identical, or substantially identical, to the original liquid composition. Thus, with boiling or evaporation, the liquid composition changes, if at all, only to a minimal or negligible extent. This is to be contrasted with non-azeotrope-like compositions in which, during boiling or evaporation, the liquid composition changes to a substantial degree. All azeotropic or azeotrope-like compositions of the present invention within the indicated ranges, as well as, certain compositions outside these ranges, are azeotrope-like. 
     Azeotropic or azeotrope-like compositions in accordance with the invention may include additional components that do not form new azeotrope-like systems, or additional components that are not in the first distillation cut. The first distillation cut is the first cut taken after the distillation column displays steady state operation under total reflux conditions. One way to determine whether the addition of a component forms a new azeotrope-like system so as to be outside of this invention is to distill a sample of the composition with the component under conditions that would be expected to separate a non-azeotropic mixture into its separate components. If the mixture containing the additional component is non-azeotrope-like, the additional component will fractionate from the azeotrope-like components. If the mixture is azeotrope-like, some finite amount of a first distillation cut will be obtained that contains all of the mixture components that is constant boiling or behaves as a single substance. 
     It follows from this that another characteristic of azeotropic or azeotrope-like compositions is that there is a range of compositions containing the same components in varying proportions that are azeotrope-like or constant boiling. All such compositions are intended to be covered by the terms “azeotropic or azeotrope-like” and “constant boiling.” As an example, it is well known that at differing pressures, the composition of a given azeotrope will vary at least slightly, as does the boiling point of the composition. Thus, an azeotrope of A and B represents a unique type of relationship, but with a variable composition depending on temperature and/or pressure. It follows that, for azeotrope-like compositions, there is a range of compositions containing the same components in varying proportions that are azeotrope-like. All such compositions are intended to be covered by the term azeotrope-like as used herein. 
     It is well-recognized in the art that it is not possible to predict the formation of azeotropes, as indicated, for example, in (U.S. Pat. No. 5,648,017 (column 3, lines 64-65) and U.S. Pat. No. 5,182,040 (column 3, lines 62-63), both of which are incorporated herein by reference. Applicants have discovered unexpectedly that HFO-1234ze and isobutylene form azeotropic and azeotrope-like compositions. 
     According to certain preferred embodiments, the azeotropic or azeotrope-like compositions of the present invention comprise, and consist essentially of, or consist of, effective amounts of trans-HFO-1234ze and isobutylene. The term “effective amounts” as used herein refers to the amount of each component which, upon combination with the other component, results in the formation of an azeotropic or azeotrope-like composition. Any of a wide variety of methods known in the art for combining the components to form a composition can be adapted for use in the present methods to produce an azeotropic or azeotrope-like composition. For example, trans-HFO-1234ze and isobutylene can be mixed, blended, or otherwise contacted by hand and/or by machine, as part of a batch or continuous reaction and/or process, or via combinations of two or more such steps. In light of the disclosure herein, those of skill in the art will be readily able to prepare azeotropic or azeotrope-like compositions according to the present invention without undue experimentation. 
     In examples where azeotropic or azeotrope-like compositions of the present invention comprise, consist essentially of, or consist of, isobutylene and HFO-1234ze, the HFO-1234ze can be present in an amount from about 82% by weight of the composition to about 96% by weight of the composition, and more preferably, between about 85% by weight of the composition to about 91% by weight of the composition. As illustrated more fully in Example 1 below, the azeotrope has been found to occur when the trans-HFO-1234ze is present in an amount between about 85% by weight of the composition to about 91% by weight of the composition, i.e., at about a concentration of 88% by weight. The boiling point of the azeotrope was experimentally measured to be at about −20.23° C. at a pressure of about 1 atmosphere. 
     As used herein, the term “about” refers to an approximate amount that falls within an acceptable range of experimental error. For example, with respect to temperature, the term “about” can mean the stated temperature plus or minus 0.05° C. 
     An azeotropic or azeotrope-like composition of the present invention can be used in polymerization mediums suitable to polymerize one or more monomers to form a polymer, or alternatively, some polymerization mediums in accordance with the present invention which are not azeotropic or azeotrope-like can be transformed into an azeotropic or azeotrope-like composition of the present invention through the simple addition of fluorinated propylene or monomer already present in the composition. For example, a polymerization medium in accordance with the present invention can comprise at least one catalyst, isobutylene and trans-HFO-1234ze. Preferably, the at least one catalyst comprises a Lewis acid, including but not limited to Lewis acids comprising aluminum, boron, gallium, or indium. For example, alkyl aluminum halides, boron halides, and organo-boron halides can be suitable catalysts. Some additional non-limiting examples of suitable Lewis acids are provided in U.S. Patent Application Publication No. 2005/0101751, the disclosure of which is hereby incorporated by reference. 
     Azeotropic or azeotrope-like compositions of isobutylene and trans-HFO-1234ze can be used in polymerization processes to produce polymers of one or more monomers. Such a polymerization process can include, for example, providing isobutylene by itself or in combination with other monomers, and contacting the isobutylene or the monomer mixture in a reactor with at least one catalyst in the presence of HFO-1234ze in an amount which forms an azeotropic or azeotrope-like composition of the present invention. 
     The compositions in accordance with the present invention improve the performance of the polymerization process, as well as the quality of a polymer product made therewith. As an initial matter, the compositions may be beneficially used to remove monomer from the reaction mixture. For example, at the end of a polymerization process, if an azeotropic or azeotrope-like composition is present, or is subsequently formed, the evaporation of solvent (e.g., trans-HFO-1234ze) facilitates the evaporation of monomer (e.g., isobutylene) from the mixture. 
     In addition, de compositions in accordance with the present invention may be used to address the problem with product agglomeration present in existing polymerization processes which use methyl chloride as a solvent. See, e.g., U.S. Pat. No. 7,423,100, column 42, paragraph 25. The compositions in accordance with the present invention could be used to improve product agglomeration properties during polymerization, i.e., by reducing, or possibly completely eliminating, the agglomeration of product. 
     Example 1 
     An ebulliometer composed of a vacuum jacketed tube with a condenser on top of which was further equipped with a quartz thermometer. 16.36 grams of HFO-1234ze was charged into the ebulliometer and the boiling point was observed. Isobutylene was then added in small increments, and the boiling point of each of the compositions was observed as the weight percentage of isobutylene was increased. A temperature depression was observed at about −20.23° C., indicating a binary minimum boiling azeotrope. The results are shown in Table 1. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Wt % trans-HFO-1234ze 
                 Wt % isobutylene 
                 T (° C.) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 100.00 
                 0.00 
                 −19.46 
               
               
                 99.76 
                 0.24 
                 −19.49 
               
               
                 98.85 
                 1.15 
                 −19.63 
               
               
                 95.62 
                 4.38 
                 −20.01 
               
               
                 90.99 
                 9.01 
                 −20.19 
               
               
                 87.82 
                 12.18 
                 −20.23 
               
               
                 84.72 
                 15.28 
                 −20.17 
               
               
                 82.05 
                 17.95 
                 −20.11 
               
               
                 78.05 
                 21.95 
                 −20.00 
               
               
                 74.57 
                 25.43 
                 −19.88 
               
               
                 70.12 
                 29.88 
                 −19.71 
               
               
                 65.84 
                 34.16 
                 −19.53 
               
               
                 61.53 
                 38.47 
                 −19.35 
               
               
                 58.85 
                 41.15 
                 −19.25 
               
               
                 56.67 
                 43.33 
                 −19.16 
               
               
                 54.26 
                 45.74 
                 −19.03 
               
               
                 52.07 
                 47.93 
                 −18.97 
               
               
                 49.25 
                 50.75 
                 −18.80 
               
               
                   
               
             
          
         
       
     
     Example 2 
     An ebulliometer composed of a vacuum jacketed tube with a condenser on top of which was further equipped with a quartz thermometer. 8.06 grams of isobutylene was charged into the ebulliometer and the boiling point was observed. HFO-1234ze was then added in small increments, and the boiling point of each of the compositions was observed as the weight percentage of HFO-1234ze was increased. No temperature depression was observed over the range of compositions tested. The results are shown in Table 2. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Wt % isobutylene 
                 Wt % trans-HFO-1234ze 
                 T (° C.) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 100.00 
                 0.00 
                 −7.40 
               
               
                 97.34 
                 2.66 
                 −8.71 
               
               
                 86.48 
                 13.52 
                 −13.61 
               
               
                 75.61 
                 24.39 
                 −16.84 
               
               
                 66.12 
                 33.88 
                 −17.84 
               
               
                 53.41 
                 46.59 
                 −18.63 
               
               
                 47.89 
                 52.11 
                 −18.91 
               
               
                 44.12 
                 55.88 
                 −19.12 
               
               
                   
               
             
          
         
       
     
     From the foregoing, it will be appreciated that although specific examples have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of this disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to particularly point out and distinctly claim the claimed subject matter.