Abstract:
Disclosed are crystalline polyphosphonates and a method to induce crystallization. These crystalline polyphosphonates exhibit a unique and advantageous combination of properties, allowing for solid state post polymerization reactions and solid state dry mixing with other polymers. Also disclosed are polymer compositions that comprise these polyphosphonates and at least one other polymer, wherein the resulting polymer compositions exhibit flame retardant properties. Further disclosed are articles of manufacture produced from these crystalline polyphosphonates and polymer compositions, such as fibers, films, coated substrates, moldings, foams, fiber-reinforced articles, or any combination thereof.

Description:
RELATED APPLICATION 
     This application claims priority to of U.S. Provisional Application Ser. No. 60/558,882 filed Apr. 2, 2004 titled “Crystalline Polyphosphonates and Methods Related Thereto”, the contents of which are incorporated herein by referenced. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to crystalline polyphosphonates that exhibit a novel combination of properties and a method for inducing crystallization. It also relates to polymer compositions comprising these branched polyphosphonates, and flame retardant coatings and articles produced therefrom. 
     BACKGROUND 
     Polyphosphonates are known to exhibit excellent fire resistance (see e.g., U.S. Pat. Nos. 2,682,522 and 4,331,614). It is known (see e.g., U.S. Pat. No. 2,682,522) that linear polyphosphonates can be produced by melt condensing a phosphonic acid diaryl ester and a bisphenol using a metal catalyst (e.g., sodium phenolate) at high temperature. This approach produced low molecular weight polyphosphonates that exhibited poor toughness. 
     Consequently, to improve toughness a synthetic approach to produce branched polyphosphonates by the transesterification process was developed (see e.g., U.S. Pat. No. 4,331,614). This approach involved the transesterification reaction of a phosphonic acid diaryl ester, a bisphenol, a branching agent (tri or tetra phenol or phosphonic acid ester), and a preferred catalyst (e.g., sodium phenolate) carried out in the melt, usually in an autoclave. Several patents have addressed the use of branching agents in polyphosphonates (see e.g., U.S. Pat. Nos. 2,716,101; 3,326,852; 4,328,174; 4,331,614; 4,374,971; 4,415,719; 5,216,113; 5,334,692; and 4,374,971). These approaches have met with some degree of success, however, the combination of properties exhibited by these polyphosphonates are still not sufficient for general acceptance in the marketplace. For example in branched polyphosphonates, the number average molecular weights as high as 200,000 g/mole are claimed with a minimum requirement of 11,000 g/mole (see e.g., U.S. Pat. No. 4,331,614) with polymer dispersities less than 2.5. Consequently these polyphosphonates exhibited high melt viscosities. This approach was successful in producing high molecular weight polyphosphonates that exhibited improved toughness, but processability was sacrificed. 
     Both linear and branched polyphosphonates produced by the transesterification process exhibited excellent flame resistance, however they generally lack hydrolytic stability and can be degraded by moisture. All polyphosphonates prepared to date are amorphous thermoplastic materials that are not known to crystallize (e.g., form ordered morphological structures). Crystallinity in organic polymers is known to impart some advantageous properties including higher heat distortation temperatures, higher thermal stability and improved solvent and moisture resistance. The ability to crystallize a polymer or prepolymer into a powder form offers several additional advantages. These include enabling additional reactions or operations that can be performed in the solid state such as subsequent reactions to increase the molecular weight or dry mixing with other polymer powders. Performing these steps in the solid state avoids the difficulty of handling high viscosity melt polymerization or melt mixing operations that require specialized equipment, are difficult and expensive. 
     SUMMARY OF THE INVENTION 
     In view of the above, there is a need for crystalline polyphosphonates and a method to induce crystallization. Therefore an object of this invention is to provide crystalline polyphosphonates. 
     Another object of this invention is to provide a method for the crystallizing polyphosphonates. This method enables the preparation of crystalline polyphosphonate powders that in turn enables solid state operations to produce polyphosphonates and polyphosphonate blends with other polymers with an unprecedented combination of properties. For example, the crystalline polyphosphonate powders can be further polymerized in a post reaction that is conducted in the solid state to produce higher molecular weight polyphosphonates with an excellent combination of fire resistance, transparency, processability and toughness. In another example, the crystalline polyphosphonate powders can be efficiently and intimately mixed with other polymer powders in the solid state. Both of these operations avoid the use of solvents and avoid having to manipulate high viscosity melts or solutions. Based on prior art, it was unexpected that polyphosphonates could be made to crystallize, since crystalline polyphosphonates are not known. 
     It is another object of the present invention to formulate polymer compositions comprising these polyphosphonates and commodity or engineering plastics. A polymer composition comprises at least one polyphosphonate of the present invention with at least one other polymer, which may be a commodity or engineering plastic, such as polycarbonate, polyacrylate, polyacrylonitrile, polyester, polyamide, polystyrene, polyurethane, polyepoxy, poly(acrylonitrile butadiene styrene), polyimide, polyarylate, poly(arylene ether), polyethylene, polypropylene, polyphenylene sulfide, poly(vinyl ester), polyvinyl chloride, bismaleimide polymer, polyanhydride, liquid crystalline polymer, cellulose polymer, or any combination thereof. The polymer composition may be produced from a crystalline polyphosphonate powder and another polymer by blending, mixing, or compounding the constituent polymers. Due to the crystalline polyphosphonates of the present invention, the resulting polymer compositions can be prepared in a dry, solid state mixing operation and avoid the problems and costs associated with handling, mixing and manipulation of high viscosity polymer melts. 
     It is yet another object of the present invention to produce articles of manufacture from these polyphosphonates or from polymer compositions comprising these polyphosphonates and other polymers. The polyphosphonates and the polymer compositions of the present invention can be used as coatings or they can be used to fabricate free-standing films, fibers, foams, molded articles, and fiber reinforced composites. 
     The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The detailed description, which follows, particularly exemplifies these embodiments. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken in connection with the accompanying drawings, in which: 
         FIG. 1  shows differential scanning calorimetry (DSC) analysis of a polyphosphonate of Example 2 before and after crystallization. 
         FIG. 2  shows DSC analysis of the polyphosphonate of Example 3 after crystallization. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention pertains to a method for preparing flame retardant, crystalline polyphosphonates having an advantageous combination of properties that allow for solid state polymerization and mixing. The terms “flame retardant”, “flame resistant”, “fire resistant” or “fire resistance”, as used herein, mean that the polymer exhibits a limiting oxygen index (LOI) of at least 27. 
     The method is conducted by exposing a polyphosphonate sample to a suitable organic solvent or solvent mixtures. The solvent or solvent mixtures can be in liquid or gaseous form. A preferred method is to dissolve the amorphous polyphosphonate in a suitable solvent and subsequently cause the polyphosphonate to precipitate by adding the polymer solution to a nonsolvent. Alternatively, the nonsolvent may be added to the polyphosphonate solution. Another preferred method to induce crystallization is to expose the polyphosphonate to the vapors of a suitable solvent until saturation occurs and subsequently remove the solvent. Another preferred method involves dissolving the amorphous polyphosphonate and then reducing the volume of solvent by thermal treatment. Alternatively, the solvent may be removed by flash evaporation by exposing the solution to high pressure and rapidly reducing the pressure. Other methods of solvent removal such as slow evaporation under vacuum or ambient pressure are also suitable. 
     The term “solvent” is used herein to describe a liquid or gaseous media that partially of fully dissolves the amorphous polyphosphonate. The term “nonsolvent” is used to describe a liquid or gaseous media that will not substantially dissolve an amorphous polyphosphonate. The term “solvent mixtures” is used to describe more than one solvent and the term “nonsolvent mixtures” is used to describe more than one nonsolvent. 
     Preferred solvents are organic solvents and can include aliphatic and aromatic hydrocarbons, glycols, amides, lactones, halogenated hydrocarbons but are not limited to these types. Most preferred solvents are those that will fully dissolve the amorphous polyphosphonate. Preferred nonsolvents include water and lower alcohols such as methanol and ethanol or ketones. Most preferred nonsolvents are those in which the crystalline polyphosphonate are completely insoluble. 
     EXAMPLES 
     Having generally described the invention, a more complete understanding thereof may be obtained by reference to the following examples that are provided for purposes of illustration only and do not limit the invention. 
     Example 1 
     Solvent Induced Crystallization of an Amorphous Polyphosphonate 
     A 50 mL round bottom flask equipped with a magnetic stirbar was placed a branched polyphosphonate (˜2 g). The polyphosphonate was prepared by the transesterification reaction of methyldiphenoxy-phosphine oxide, 4,4′-dihydroxydiphenylphenyl tetraphenylphosphonium phenolate and 1,1,1-tris(4-hydroxyphenyl) ethane according to the U.S. patent application Ser. No. 10/374,829, filed Feb. 24, 2003 and is incorporated by reference. The branched polyphosphonate exhibited a relative viscosity of 1.13 and a Tg of ˜137° C. and no melting transition by DSC. Methylene chloride (30 mL) was added to the flask and the polyphosphonate dissolved over about 2 hours with stirring. This solution was subsequently poured into a beaker containing methanol (˜150 mL). A precipitate formed immediately, additional methanol ˜(100 mL) was added and the mixture was allowed to stand for ˜1 hour. The off-white solid was isolated by filtration, washed repeatedly with methanol and allowed to air dry for ˜1 hour. The solid was further dried by heating to 70° C. in a forced air oven for ˜12 hours. The final solid was off-white with a slight yellow color. This solid was analyzed by DSC and it exhibited no Tg but a sharp crystalline melting transition from 164° C. 
     Example 2 
     Solvent Induced Crystallization of an Amorphous Polyphosphonate 
     A 500 mL round bottom flask equipped with a magnetic stirbar was placed a branched polyphosphonate (5.2 g). The polyphosphonate was prepared by the transesterification reaction of methyldiphenoxy-phosphine oxide, 4,4′-dihydroxydiphenyl, tetraphenylphosphonium phenolate and 1,1,1-tris(4-hydroxyphenyl)ethane according to the U.S. patent application Ser. No. 10/374,829, filed Feb. 24, 2003 and is incorporated by reference. The branched polyphosphonate exhibited a relative viscosity of 1.13 and a Tg of ˜137° C. and no melting transition by DSC. Methylene chloride (100 mL) was added to the flask and the polyphosphonate dissolved over about 0.5 hours with stirring. This solution was subsequently placed on a rotary evaporator and the solvent was removed. Warm acetone (˜25 mL) was added to the remaining white solid to form a solution. The solution was scratched with a spatula and white crystals immediately formed. The white crystals were collected by filtration, washed with acetone and air dried. The solid was further dried by heating to 60° C. in a forced air oven for ˜12 hours. The final solid (4.52 g) was off-white in color. This solid was analyzed by differential scanning calorimetry (DSC) and it exhibited no Tg but a sharp crystalline melting transition from 164° C. 
     The changes in morphology due to the solvent treatment are readily apparent by differential scanning calorimetry (DSC) analysis depicted in  FIG. 1  below. Before applying the crystallization method (e.g., before crystallization), only a glass transition is evident with the midpoint occurring around 137° C. After applying the crystallization method (e.g., after crystallization), no glass transition is evident and a new crystalline melting transition appears around 164° C. 
     Example 3 
     Solvent Induced Crystallization of an Amorphous Polyphosphonate 
     A 500 mL round bottom flask equipped with a magnetic stirbar was placed a branched polyphosphonate (5.0 g). The polyphosphonate was prepared by the transesterification reaction of methyldiphenoxy phosphine oxide, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), tetraphenylphosphonium phenolate and 1,1,1-tris(4-hydroxyphenyl)ethane according to the U.S. patent application Ser. No. 10/374,829, filed Feb. 24, 2003 and is incorporated by reference. The branched polyphosphonate exhibited a relative viscosity of 1.12 and a Tg of 104° C. and no melting transition by DSC. Methylene chloride (200 mL) was added to the flask and the polyphosphonate dissolved over about 0.5 hours with stirring. The solution volume was reduced to ˜30 mL by evaporation and was subsequently poured into a crystallizing dish and heated to about 80° C. for several hours in an oven. The material was further heated to about 80° C. in a vacuum oven. The white solid was manually milled under mild pressure. This solid was analyzed by DSC and it exhibited no Tg but a sharp crystalline melting transition from 109° C. 
     The DSC curve of the polyphosphonate of Example 3 after crystallization is presented in  FIG. 2 . This material exhibits a sharp melting transition centered at 109° C. Prior to crystallization, this material was amorphous and exhibited a Tg near 104° C. In this case, the heat distortion temperature is slightly increased. 
     The results indicate that this is a novel approach to induce crystallinity into polyphosphonates. The heat distortion temperature is increased as evidenced by DSC. Further, it may be possible to effect this change in the solid state by exposing the polyphosphonate to solvent vapors. 
     Example 4 
     Preparation and Testing of a Crystalline Polyphosphonate/Polymer Composition 
     A composition comprising the crystalline polyphosphonate of Example 3 and a commercially available polycarbonate (Makrolon 3107, available from Bayer A.G.). The composition consisted of 80% by weight Makrolon 3107 and 20% by weight crystalline polyphosphonate of Example 3. Multiple samples (3.2 mm thick) from this composition were subjected to UL-94 test. The results were a flame time of 6 seconds for the first two burns and a total of 19 seconds for ten burns. These results correspond to a rating of V0. The Makrolon 3107 without the crystalline polyphosphonate additive exhibited a rating of V2 or higher. 
     As noted herein, the present invention is applicable to crystalline polyphosphonates, and methods and applications related thereto. The present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures, numerous solvents, solvent combinations and methods to introduce the solvent, to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the present specification.