||||||||||||||| US005208298A United States Patent (19) 11 Patent Number: 5,208,298 Chung et al. (45) Date of Patent: May 4, 1993

(54) STABLE SOLUTION OF POLYBENZMIDAZOLE AND FOREIGN PATENT DOCUMENTS POLYSULFONS BLENDS 0240302 10/1987 European Pat. Off. . (75) Inventors: Tai-Shung Chung, Randolph; Arthur 91/04300 4/1991 PCT Int'l Appl. . G. Schlask, Roselle Park; Dieter Primary Examiner-Paul R. Michl Kurschus, Bayville, all of N.J. Assistant Examiner-Tae H. Yoon (73) Assignee: Hoechst Celanese Corp., Somerville, Attorney, Agent, or Firm-J. M. Hunter, Jr. N.J. (57) ABSTRACT (21) Appl. No.: 865,386 A stable solution of polybenzinidazole resin containing 22) Filed: Apr. 8, 1992 from approximately 10 to approximately 35 weight 51 Int. Cl...... C08L 77/06; C08L 81/06; percent of resins and from approximately 65 to approxi CO8L 79/04 mately 90 weight percent of a suitable solvent, the resins (52) U.S. C...... 525/435; 524/606; consist of from approximately 70 to approximately 95 524/609, 524/612; 525/540; 525/906 weight percent of polybenzimidazole and from approxi (58) Field of Search ...... 524/606, 609, 612, 720; mately 5 to approximately 30 weight percent of polysul 525/435, 540,906 fone, wherein the solution is substantially free of or ganic salt. The solution is useful for the production of (56) References Cited films, and molded articles exhibiting enhanced U.S. PATENT DOCUMENTS mechanical properties. 3,441,640 4/1969 Santangelo ...... 524/422 4,340,697 7/1982 Aya et al...... 525/906 20 Claims, 4 Drawing Sheets U.S. Patent May 4, 1993 Sheet 1 of 4 5,208,298

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5,208,298 1. 2 the Solution, wherein the solution is substantially free of STABLE SOLUTION OF POLYBENZMIDAZOLE organic salt. AND POLYSULFONS BLENDS Another embodiment of the invention is directed to a prepared from a stable solution of polyben FIELD OF THE INVENTION Zinidazole resin solution consisting of from approxi The present invention relates to a stable solution of mately 10 to approximately 35 weight percent of the aromatic polybenzimidazole and polysulfone resins resin and from approximately 65 to approximately 90 which is substantially free of organic salts. The solution weight percent of a suitable solvent, based on the total is useful for the production of films, fibers and molded weight of the solution, the resin component consisting articles. O essentially of from approximately 70 to approximately 95 weight percent of polybenzimidazole resin and from BACKGROUND ART approximately 5 to approximately 30 weight percent of Aromatic polybenzimidazoles are a unique class of polysulfone resin, based on the total weight of the res intractable, i.e., not melt processable, organic polymers ins, wherein the resins solution is substantially free of which are high temperature resistant, as well as chemi 15 organic salts, by the process of: cal and oxidative resistant. Because these polymers are (a) preparing a stable solution of polybenzimidazole not melt processable, it is difficult to form them into resin consisting of from approximately 10 to approxi film, fibers and molded articles. To enhance the melt mately 35 weight percent of resin and from approxi processability, reduce the cost of products made there mately 65 to approximately 90 weight percent of a suit from, and moisture takeup of the finished product, poly able solvent, based on the total weight of the solution, is often blended with a tractable poly the resin consisting of from approximately 70 to approx mer. One useful tractable polymers useful for blending imately 95 weight percent of polybenzimidazole and with polybenzimidazole is aromatic polysulfones. How from approximately 5 to approximately 30 weight per ever, desirable mechanical and thermal properties are significantly reduced by the addition of these melt pro 25 cent of polysulfone, based on the total weight of the cessable polymers; the degree of reduction is usually resins present in the solution, wherein the solution is proportional to the weight percent of the melt process substantially free of organic salts; able polymer addition. Blends of polybenzimidazole (b) fabricating a fiber from the solution under sub and polysulfone are generally prepared by a process stantially moisture-free conditions; known as solution blending. Solution blending involves 30 (c) evaporating the solvent from the fiber; dissolving both polymers in a suitable solvent to form a (d) washing the fiber with a non-solvent; and polybenzimidazole-containing dope. The dope can be (e) drying the fiber at a low temperature utilized to form films or fibers by conventional tech The resins solution is stable for long periods of time, and niques, or the resins blend can be precipitated out of fibers produced from the solution exhibit enhanced solution utilizing a non-solvent. The precipitate can be 35 mechanical and thermal properties which make them dried to form a particulate blend which is useful for useful as flame retardant materials. forming molded articles and the like. BRIEF DESCRIPTION OF THE DRAWINGS When solution of polybenzimidazole and polysulfone in the range of from approximately 1 to approximately While the specification concludes with claims partic 99 weight percent of polybenzimidazole and approxi ularly pointing out and distinctly claiming the present mately 1 to approximately 99 weight percent of polysul invention, it is believed that the present invention will fone are dissolved in a suitable solvent, the polyben be better understood from the following description in zimidazole will separate out of the solution after a short conjunction with the accompanying drawings in which: period of time unless it is stabilized with an organic salt, FIG. 1 is a graph of the viscosities of various weight e.g., lithium chloride. While the addition of a stabilizer 45 ratios of stable solutions containing 21 weight percent has lengthened the time of solution stability, it has re of polybenzimidazole and polysulfone resins dissolved sulted in the adverse effecting the mechanical and ther in N,N'- solutions; mal properties of fibers spun from the dope. It has now FIG. 2 is a graph of the break elongation of dry-spun been discovered that solutions of polybenzimidazole fibers prepared from a stable solution containing 80 and polysulfone within the range of approximately 10 to 50 weight percent polybenzimidazole and 20 weight per approximately 35 weight percent of polysulfone and cent polysulfone; approximately 65 to approximately 90 weight percent FIG. 3 is a graph of the tensile modulus of dry-spun of polybenzimidazole which are substantially free of fibers prepared from a stable solution containing 80 organic salts are stable for long periods of time without weight percent polybenzimidazole and 20 weight per phase separation. Fibers produced from the solution 55 cent polysulfone; and exhibit enhanced mechanical and thermal properties. FIG. 4 is a graphical representation of the tensile strength of dry-spun fibers prepared from a stable solu SUMMARY OF THE INVENTION tion containing 80 weight percent polybenzimidazole The present invention is directed to a stable solution and 20 weight percent polysulfone. of polybenzimidazole resin consisting of from approxi mately 10 to approximately 35 weight percent of resin DETAILED DESCRIPTION OF THE and from approximately 65 to approximately 90 weight INVENTION percent of a suitable solvent, based on the total weight Generally, the aromatic polybenzimidazole useful in of the solution, the resin component consisting of from the present invention may be any polybenzimidazole approximately 70 to approximately 95 weight percent 65 resins known to those skilled in the art. Typical poly of polybenzimidazole (PBI) and from approximately 5 mers of this class and their preparation are more fully to approximately 30 weight percent of polysulfone described in U.S. Pat. No. 2,895,946; U.S. Pat. No. (PS), based on the total weight of the resins present in 26,065; and the Journal of Polymer Science, Vol. 50, 5,208,298 3 4. pages 511-539 (1961), which are herein incorporated by poly-2,2'-(m-phenylene)-5,5'-dicbenzimidazole) sul reference in their entirety. These polybenzinidazoles fone; consist essentially of recurring units of the Formulae I poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole) meth and II: ane; Formula I is: poly-2,2'-(m phenylene)-5',5'-di(benzimidazole) propane-2,2; and poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole) ethylene-1,2; where the double bonds of the ethylene groups are O intact in the final polymer. A preferred polybenzirpidazole for use in the present invention is poly-2,2'-(n-phenylene)-5,5'-biben wherein Ari represents a tetravalent aromatic moiety zimidazole, the recurring unit of which is: having the formula: 15

N N A. W C C V / 20 N H h Processes for preparing the aromatic polyben IOOL 25 Zimidazoles of the invention are described in U.S. Pat. Nos. 3,441,640; 3,433,772; 3,509,108; 3,549,603; wherein R1 is O, SO2, CH-CH, C(CF3)2 or (CH2) and 3,526,693; 3,552,389; 3,619,453; 3,671,491; 3,969,430; wherein x is an integer of from 1 to 4; and Ar2 represents and 4,020,142 all of which are herein incorporated by a divalent aromatic moiety having the formula: reference in their entirety. 3O The addition of a minor amount of polysulfone to polybenzinidazole can decrease moisture takeup, re duce the process temperature, increase the tractability, and reduce the cost of polybenzimidazole products. TO TO O. Generally, the polysulfones of the present invention 35 and their method of preparation are well known in the art; see, for example, U.S. Pat. Nos. 3,709,841 and 4,273,903 both of which are herein incorporated by reference in their entirety. The preparation of a poly TOIO ner in which part of the aromatic rings are substituted 40 with hydroxysulfonyl radicals (SO3H), known as sul wherein R2 is O, SO2, CH=CH, C(CF3)2 or (CH2) and fonic groups); other references are U.S. Pat. No. wherein x is an integer of from 1 to 4. 4,273,903 and United Kingdom Pat. No. 1,350,342. Formula II is: The polysulfone contains recurring units of the for mula: 45 N Z N N / t-O-Ar-SO2-Ar-et-O-Ars-R3-Aré-o- wherein Ar, Art, Ars, and Ar6 are aromatic moieties H 50 having from approximately 6 to approximately 18 car wherein Z is an aromatic nucleus having the nitrogen bon atoms, or aromatic moieties having the following atoms forming the benzimidazole ring paired upon adja formula: cent, carbon atoms of the aromatic nucleus. Examples of typical polybenzimidazoles which may 55 be used in the present invention are as follows: poly-2,2'-(n-phenylene)-5,5'-bibenzimidazole; poly-2,2'-(pyridylene-3',5')-5,5'-bibenzimidazole; poly-2,2'-(furylene 2',5')-5,5'-bibenzimidazole; poly-2,2'-(naphthalene 1",6")-5,5'-bibenzimidazole; 60 wherein R represents C(CH3), SO2, S, O, or mixtures poly-2,2'-(biphenylene-4",4")-5,5'-bibenzimidazole; thereof; R represents a divalent aliphatic moiety con poly-2,2'-amylene-5,5'-bibenzimidazole; taining up to 6 carbon atoms, or mixtures thereof, and a poly-2,2'-octamethylene-5,5'-bibenzinidazole; has the value greater than approximately 0.5 to approxi poly-2,6'-(m-phenylene)-diimidazobenzene; mately 1.0, b has the value of 0 or less than approxi poly-2,2'-cyclohexeneyl-5,5'-bibenzimidazole; 65 mately 0.5, and the sum of a and b is equal to 1.0. In the poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole) ether; preferred polysulfones, the number of sulfone linking poly 2,2'-(m-phenylene)-5,5'-di(benzimidazole) sul groups relative to all others is typically 1 out of 3. These fide; relative inexpensive polymers exhibit good physical 5,208,298 5 6 properties, e.g., thermal resistance, impact strength, pressure of from approximately 2 to approximately 7 etc., and are readily blendable with polybenzimidazole. atmospheres for approximately 2 hours at a temperature The polysulfones from Amoco Corporation, known of from approximately 25 to approximately 125 C. by the registered names of Udel (RP1700, Radel The resulting solution is preferably filtered to remove (RA400, and Victrex PES (R4100G from ICC are the any undissolved polymer prior to being processed. Op most preferred. Udel (RP1700 is believed to be prepared tionally, the two polymers may be individually dis from a nucleophilic substitution reaction between a solved in the solvent and subsequently mixed together sodium salt of a bispheol A and 4,4'-dichlorodiphenyl in the desired proportions. sulfone. These polysulfones are amorphous polymers; a The solution may be prepared into films, fibers and combination of polysulfones may be blended in the O molded articles by conventional techniques. Films may compositions of the invention. be readily prepared from the solution of the present The invention is directed to a stable solution contain invention by conventional casting processes known in ing from approximately 10 to approximately 35 weight the art. The solvent may be removed from the film by percent of resin, i.e., polymer solids, and from approxi washing in a nonsolvent such as water or a C to C4 mately 65 to approximately 90 weight perent of a suit 5 aliphatic alcohol, and drying at a low relative humidity able solvent, based on the total weight of the solution, and moderate temperature of less than approximately wherein the solution is substantially free of organic salt. 40 C. Typically, the solution contains approximately 20 to Fibers may be prepared from the polymeric solution approximately 30 percent by weight of resin and from of the invention by wet spinning methods known in the approximately 70 to approximately 80 weight percent art; see for instance, commonly assigned U.S. Pat. No. of solvent, and preferably, the solution contains approx 3,441,640 herein incorporated by reference in its en imately 28 weight percent of resin and approximately 72 tirety. Commonly assigned U.S. Pat. No. 3,851,025 weight percent of solvent, based on the total weight of herein incorporated by reference in its entirety, which the solution, wherein the solution is substantially free of described a process for preparing a hollow polyben organic salt. 25 zimidazole filaments may be utilized to prepare fila It has been discovered that if the dope is to be mis ments from the resin solution to the present invention. cibly stable without the addition of an organic salt The fibers are useful in the production of fire retardant stabilizer such as lithium chloride, the ratio of polyben fabrics. Preferably, the spinning solution will contain zimidazole to polysulfone must be maintained within from approximately 28 weight percent of polymer certain range limits. Generally, the resin solution con 30 solids, and exhibit a viscosity of from approximately tains from approximately 70 to approximately 95 weight 1,000 to approximately 3,000 poise measured at a ten percent of polybenzimidazole and from approximately 5 perature of 25 C. and a shear rate of approximately .0 to approximately 30 weight percent of polysulfone, rpm. based on the total weight of resins present in the Solu The filtered, stable resin solution at a temperature of tion. Typically, the solution contains from approxi 35 approximately 70 to approximately 150 C., is extruded mately 75 to approximately 85 weight percent of poly through a plurality of extrusion orifices, e.g., from 50 to benzimidazole and approximately 15 to approximately 300 orifices. These extursion orifices are generally in the 25 weight percent of polysulfone, based on the total form of a spinneret having from approximately 50 to weight of resins present, and preferably, the resin solu approximately 100 holes. Typically, the orifices utilized tion contains approximately 80 weight percent of poly 40 in the process of the present invention have a diameter benzimidazole and approximately 20 weight percent of of approximately 20 to approximately 200 microns, and polysulfone, based on the total weight of resins present preferably a diameter of from approximately 30 to ap in the solution; it has been discovered that these pre proximately 50 microns. The face of the spinneret is ferred weight percents are stable at ambient conditions heated from approximately 130 to approximately 150 for at least two month under stagnant conditions. 45 C. during extrusion. The solution is extruded vertically The polymeric solutions of the present invention are downward into a gaseous atmosphere to produce fibers prepared by dissolving an aromatic polybenzimidazole which are drawn, washed to remove residual solvent and a polysulfone in a suitable solvent. While any sub and collected. stance that will dissolve both polybenzinidazole and One embodiment of the invention is a process for polysulfone is suitable for forming the solution of the SO preparing a polybenzimidazole fiber from a stable solu invention, generally, known useful solvents may be tion of polybenzimidazole resin, the solution consisting selected from N,N'-dimethylacetmaide, N,N'-dimethyl of from approximately 10 to 35 weight percent of resin formamide, dimethylsulfoxide, and N-methyl-2-pyrroli and from approximately 65 to approximately 90 weight done, , acetic acid, , polyphos percent of a suitable solvent, based on the total weight phoric acid, and methanesulfonci acid. Particularly, the 55 of the solution, the resin component consisting of from preferred solvent is N,N'-dimethylacetamide (DMAc) approximately 70 to approximately 95 weight percent having a concentration of from approximatley 90 to of benzimidazole and from approximately 5 to approxi approximately 100 percent, and preferably approxi mately 30 weight percent of polysulfone, based on the mately 99 percent by weight. total weight of resins present in the solution, by the Methods of dissolving the polymers in a variety of 60 steps of: W solvents are known to those skilled in the art. One suit (a) preparing a stable solution of polybenzinidazole able method requires drying the starting polymers to a resin consisting of from approximately 10 to approxi moisture level of approximately 2 weight percent in a mately 35 weight percent of resin and from approxi vacuum oven at a temperature of approximately 100 C. mately 65 to approximately 90 weight percent of a suit to approximately 160° C. for approximately 10 to ap 65 able solvent, based on the total weight of the solution, proximately 16 hours. Preferred conditions for dis the resins consisting of from approximately 70 to ap solving the polymers comprise heating the mixture of proximately 95 weight percent of polybenzimidazole polymer and solvent in a stainless steel reactor at a and from approximately 5 to approximately 30 weight 5,208,298 7 8 percent of polysulfone, based on the total weight of tive fillers are selected from calcium silicate, silica, resins present in the solution, wherein the solution is clays, talc, mica, polytetrafluoroethylene, graphite, substantially free of organic salts; alumina trihydrate, sodium aluminum carbonate, bar (b) extruding a fiber from the solution under substan ium ferrite, etc. tially moisture-free conditions; 5 (c) evaporating the solvent from the fiber; Following are examples illustrative of preparing (d) washing the fiber with a non-solvent; and highly porous particles in accordance with the present (e) drying the fiber at a low temperature. invention. They are provided for purposes of exemplifi Typically, the spinning solution contains from ap cation only as should be appreciated from the foregoing proximately 20 to approximately 30 weight percent of 10 discussion. resin and approximately 70 to approximately 80 weight percent of a suitable solvent, based on the total weight EXAMPLE 1. of the solution, wherein the solution is substantially free Solution Preparation of organic salts. Preferably, the solution contains ap proximately 28 weight percent resin and approximately 15 Several batches of dope containing no lithium chlo 72 weight percent of a suitable solvent, based on the ride were prepared by dissolving PBI in DMAc at ap total weight of the solution, wherein the solution is proximately 90° C. overnight and blending therewith a substantially free of organic salts. solution of PS dissolved in DMA.c. Poly-2,2'-(m- Typically, the spinning solution contains from ap phylene)-5,5'-bibenzimidazole exhibiting an intrinsic proximately 75 to approximately 85 weight percent of 20 viscosity of 0.77 di/gm, a glass transition temperature of polybenzinidazole and approximately 15 to approxi approximately 435 C. manufactured by Hoechst Celan mately 25 weight percent of polysulfone, based on the ese Corporation, and a Udel (R) P1700 polysulfone (PS) total weight of resins present in the solution. Preferably, manufactured by Amoco Corporation were utilized to the solution contains approximately 80 weight percent prepare the solutions. Solutions containing 21 weight of polybenzinidazole and approximately 20 weight 25 percent of polysulfone, based on the total weight of percent of resin and 79 weight percent of a suitable resins present in the solution. solvent, i.e., DMAc, wherein the resin contained from During fabrication the spinning solution is extruded 70 to 95 weight percent of PBI and from 5 to 30 weight vertically downward into a gaseous atmosphere percent of PS were prepared for stability evaluation. through a plurality of extrusion orifices having a diame 30 The two Solutions mixed together well and appeared to ter of approximately 20 to approximately 200 microns be clear. The solution of 80 wt.% PBI and 20 wt.% PS to form a plurality of fibers and simultaneously drawing appeared to be most stable after long periods of stagna the filaments, with an initial draw ratio of from approxi t1O. mately 2:1 to approximately 20:1. The fibers may be hot The viscosity of the solutions were evaluated. FIG. 1 drawn at a temperature in the range of from approxi 35 illustrates the viscosities of dilute resin solutions con mately 350 to approximately 500 C. and a ratio of from approximately 1.5:1 to approximately 10:1 to pro taining 21 weight percent of resin and 79 weight percent duce fibers having a denier per filament of approxi of DMAC, based on the total weight of the solution, mately 0.5 to approximately 25 and a tenacity of at least wherein the resin contains different weight percentages 2.5 grams per denier. After drying, the hot drawn fila 40 of PBI and PS at temperatures of 25,35, 45° and 55° C. ments may be subject to sulfonation. Sulfonation is The viscosity of a solution containing 80 weight percent designed to stabilize to fiber against shrinkage. Gener of PBI and 20 weight percent of PS, based on the total ally, sulfonation requires contacting the filament with a weight of the solution exhibited a viscosity of approxi solution of sulfuric acid, dring and heat treating at a mately 70 poise at a temperature of 25 C. and a shear temperature of from approximately 200 to approxi 45 rate of 1.0 rpm. The viscosities were measured accord mately 500 C. and drawing at a ratio of from approxi ing to ASTM No. D2857. mately 0.95:1 to approximately 1:1. There is also a sub stantial weight gain of the as-spun fiber upon sulfona EXAMPLE 2 tion. The fiber can gain an additional 20 percent weight Preparation of As-spun Fibers by sulfonation. This weight increase in sulfonation com 50 ponents rather than polybenzimidazole is economical, The stable spinning solution of 80 wt.% PBI and 20 and provides a fiber which has enhanced mechanical wt% PS (25.6 wt.% polymer solids) prepared in Exam properties. ple 1 was utilized in a dry-spinning process to produce Molded articles may be prepared from the solution of fibers. Generally, dry-spun fibers exhibited mechanical the invention by first precipitating or atomizing parti 55 properties Superior to that of wet-spun fibers. The solu cles using a non-solvent such as water or alcohol. The tion at a temperature of approximately 70° C. was fil particles may be consolidated into densified shaped articles at temperatures of up to approximately 800 C. tered and metered by a gear pump to a spinneret having and pressures of up to approximately 60 ksi. A solid 75 holes, and a takeup speed of approximately 200 me filler and/or reinforcement agent in the amount of ap ter/min. The Solution was extruded vertically down proximately 1 to approximately 40 weight percent may ward into a hot stream of circulating N, gas in a dry be added to the molded article if desirable. Representa column approximately 6.6 meters long at a temperature tive fibers which serve as reinforcement are selected of approximately 200 C. Fibers were formed when from glass fibers, , graphitic carbon fibers, most of the DMAC was vaporized, and residual DMAc amorphous carbon fibers, synthetic polymeric fibers, 65 in the as-spun fiber was removed by washing with wa aluminum fibers, aluminum silica fibers, aluminum ixude ter. The properties of as-spun fibers, analyzed in accor fibers, titanium fibers, magnesium fibers, rock wool dance with ASTM No. D3822, are presented below in fiber, wollastonite fibers, steel fibers, etc. Representa Table I for comparison. 5,208,298 9 10 TABLE I TABLE III-continued Fiber Properties of As-spun 8020 PBI/PS Fiber Tensile Properties of Hot Drawn and Stabilized Fibers Denier, Init. Mod. Tenacity, Elong., Init. Mod. Tenacity, Elong. Sample (dpf) (gm/d) (gm/d ) (%) 5 Sample LiC (g/d) (gpd) (%) PBAPS 4.46 43.5 4. 82.5 Stabilized Lic PBAPS 5.82 32.2 1.374 06.0 no LiC The elongation of a hot drawn fiber prepared from a g/d x 8.83 = cNtex solution substantially free of lithium chloride is in O proved over that of a fiber prepared from a solution As-spun fibers containing no lithium chloride exhibit containing lithium chloride. enhanced elongation without significant sacrifice of EXAMPLE 5 denier, modulus and tenacity. Sulfur Content of Stabilized Fibers EXAMPLE 3 15 The stabilized fibers of Example 4 were analyzed for Hot Drawn Fibers sulfur and SO3H content, and the change in denier. The To improve fiber properties, the as-spun fibers pre content of S and SO3H are presented below in Table 4 pared in Example 2 were hot-drawn by passing the for comparison. dried fibers through a muffle furnace at a temperature 20 TABLE IV of from approximately 380 to approximately 400 C. at - Sulfur and SO3H Content in Hot Drawn, Sulfonated Fibers a rate of approximately 1.5 meter/min. Skewed rolls Sul. S Cont" SO3H Cont Denier Change before and after the muffle furnace accurately main Sample fonated (%) (%) (%) tained the fibers at proper speeds. The spin-line tension PBAPS No 1.75 .. O. 25 80/20 caused the fibers to elongate, and the polymeric struc no LiC ture within the fibers was believed to be better oriented. PBAPS Yes 8.55 2.64 2.85 The tensile properties of hot drawn PBI/PS fibers, and 80/20 neat PBI fibers are presented below in Table II for no LiC comparison. PBAPS No 153 .O. 0. 30 80/20 TABLE II LiCl PBAPS Yes 6.38 16.5 16.55 Tensile Properties of Hot Drawn Fibers 80/20 Denier, Draw Init. Mod. Tenacity. Elong. LiC Sample (dpf) Ratio (gm/d) (gm/d ) (%) S content was measured by an analytical method. SO3 content was calculated by assuming that all S becomes SOH. PBAPS 1.98 4.0 12. 3.6 7.3 35 Average denier change was calculated based on the change of fiber denier before (80/20) at 420 C. and after sulfonation. w LiCl PBAPS 1.00 4.5 134. 4.84 5.9 (80/20) at 420 C. FIG. 2 illustrates the break elongation of dry-spun no LiCl fibers prepared from a solution containing 80 weight PB i 2.0 910 4.0 31.9 40 percent of polybenzimidazole and 20 weight percent of Control at 440 C. polysulfone with and without lithium chloride and no LiCl drawn at 400 and 420 C. The draw ratio of fiber pre g/d x 8.83 se citex pared from a solution containing no lithium chloride show a significant improvement over fibers prepared EXAMPLE 4 45 from a Solution containing lithium chloride at the same break elongation. Fiber Stabilization FIG. 3 illustrates the tensile modulus of dry-spun The hot drawn fibers prepared similar to those of fibers prepared from a solution containing 80 weight Example 3, but with different draw ratios, were stabi percent of polybenzimidazole and 20 weight percent of lized utilizing the sulfonation process described herein 50 polysulfone with and without lithium chloride and before. The tensile properties of hot drawn and stabi drawn at 400' and 420 C. The fiber prepared from a lized fibers are presented below in Table III for compar Solution containing no lithium chloride exhibit greater tensile moduli at higher draw ratios. SO. FIG. 4 illustrates the tensile strength of dry-spun TABLE III 55 fibers prepared from a solution containing 80 weight Tensile Properties of Hot Drawn and Stabilized Fibers percent of polybenzimidazole and 20 weight percent of Init. Mod. Tenacity, Elong., polysulfone with and without lithium chloride and Sample iC (g/d) (gpd) (%) drawn at 400 and 420 C. The fibers prepared from a PBAPS 9.8 3.77 6. Solution containing no lithium chloride exhibit greater 80/20 60 tensile strength at higher draw ratios. PBAPS s 58.7 2.6 9. We claim: 80/20 stabilized 1. A stable solution of polybenzimidazole resin con PBAPS yes 108.6 2.96 3.63 sisting of from approximately 10 to approximately 35 80/20 weight percent of resin and from approximately 65 to PBAPS yes 75 2.24 5.9 6S 80/20 approximately 90 weight percent of a suitable solvent, stabilized based on the total weight of the solution, the resin con PB yes 45 2.7 30.0 sisting of from approximately 70 to approximately 95 Control weight percent of polybenzimidazole and from approxi 5,208,298 11 12 mately 5 to approximately 30 weight percent of polysul imately 70 to approximately 95 weight percent of fone, based on the total weight of the resins present in polybenzimidazole and from approximately 5 to the solution, wherein the solution is substantially free of approximately 30 weight percent of polysulfone, organic salts. based on the total weight of resins present in the 2. The solution according to claim 1 wherein the solution, wherein the solution is substantially free polybenzimidazole is poly 2,2'-(m-phenylene)-5,5'- of organic salts; bibenzinidazole. (b) extruding a fiber from the solution under substan 3. The solution according to claim 2 wherein the tially moisture-free conditions; polysulfone is of the formula: (c) evaporating the solvent from the fiber; O (d) washing the fiber with a non-solvent; and (e) drying the fiber at a low temperature --o-Ar-so-Ar-i-o-Ar-R-Ar-O- wherein the fiber exhibits enhanced elongation and sulfur weight gain. wherein Ar3, Ari, Ars, and Arare aromatic moieties having from approximately 6 to approximately 18 car 11. The fiber according to claim 10 wherein the poly 15 benzimidazole is poly-2,2'-(m-phenylene)-5,5'-biben bon atoms, or aromatic moieties having the following zimidazole. formula: 12. The fiber according to claim 11 wherein the poly sulfone is of the formula:

20 -to-Ar-SO-Ar-at-o-Ars-R3-Aré-o- wherein Art, Art, Ars, and Arare aromatic moieties wherein R4 represents C(CH3), SO2, S, O, or mixtures having from approximately 6 to approximately 18 car thereof; R3 represents a divalent aliphatic moiety con bon atoms, or aromatic moieties having the following taining up to 6 carbon atoms, or mixtures thereof; and a 25 formula: has the value greater than approximately 0.5 to approxi mately 1.0, b has the value of 0 or less than approxi mately 0.5, and the sum of a and b is equal to 1.0. 4. The solution according to claim 3 wherein the resins consist essentially of approximately 80 weight 30 percent of polybenzimidazole and approximately 20 weight percent of polysulfone. wherein R represents C(CH3), SO2, S, O, or mixtures 5. The solution according to claim 4 wherein the thereof; R represents a divalent aliphatic moiety con solution consist essentially of approximately 28 weight taining up to 6 carbon atoms, or mixtures thereof, and a percent of resin and approximately 72 weight percent of 35 has the value greater than approximately 0.5 to approxi solvent, based on the total weight of the solution. mately 1.0, b has the value of 0 or less than approxi 6. The solution according to claim 1 wherein the mately 0.5, and the sum of a and b is equal to 1.0. solvent is selected from the group consisting of N,N'- 13. The fiber according to claim 12 wherein the resins dimethilyacetamide, N,N'-dimethylformamide, dimeth consist essentially of approximately 80 weight percent ylsulfoxide, and N-methyl-2-pyrrolidone, formic acid, of polybenzimidazole and approximately 20 weight acetic acid, sulfuric acid, polyphosphoric acid, and percent of polysulfone. . 14. The fiber according to claim 13 wherein the solu 7. The solution according to claim 5 wherein the tion consist essentially of approximately 28 weight per solvent (1 N,N'-dimethylacetamide. cent of resin and approximately 72 weight percent of 8. The solution according to claim 5 having a viscos 45 solvent. ity of approximately 1,000 to approximately 3,000 poise 15. The fiber according to claim 14 wherein the sol at a temperature of approximately 25 C. and a shear vent is selected from the group consisting of N,N'- rate of approximately 1.0 rpm. dimethilyacetamide, N,N'-dimethylformamide, dimeth 9. The solution according to claim 7 useful for the ylsulfoxide, and N methyl-2-pyrrolidone, formic acid, production of films, fibers and molded articles. 50 acetic acid, sulfuric acid, polyphosphoric acid, and 10. A fiber prepared from a stable solution of poly methanesulfonic acid. benzimidazole resin consisting of from approximately 5 16. The fiber according to claim 15 which is con to approximately 30 weight percent of the resin and tacted with a sulfonating agent and heat treated at a from approximately 70 to approximately 95 weight temperature of approximately 200 to approximately percent of a suitable solvent, based on the total weight 55 500 C. of the solution, the resin component consisting essen 17. The fiber according to claim 10 wherein the non tially of from approximately 70 to approximately 95 solvent is selected from water and C1 to C4 aliphatic weight percent of polybenzimidazole resin and from alcohols. approximately 5 to approximately 30 weight percent of 18. The fiber according to claim 16 wherein the as polysulfone resin, based on the total weight of resins 60 spun fiber is draw after extrusion at a draw ratio of present in the solution, wherein the resins solution is approximately 2:1 to approximately 20:1. substantially free of organic salts, by the process of: 19. The fiber according to claim 18 exhibiting an (a) preparing a stable solution of polybenzimidazole elongation of at least approximately 85 percent. resin consisting of from approximately 10 to ap 20. The fiber according to claim 19 which is hot proximately 35 weight percent of resin and from 65 drawn at a draw ratio of approximately 1.5:1.0 to ap approximately 65 to approximately 90 weight per proximately 10:1 and at a temperature of from approxi cent of a suitable solvent, based on the total weight mately 350° to approximately 500 C. of the solution, the resin consisting of from approx k . . .