US2579451A - Polymeric materials - Google Patents

Description

Patented Dec. 18, 1951 UNITED STATES PATENT OFFICE POLYMERIC MATERIALS Allen E. Poison, Tallmadge, Ohio, assignor to E. E. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application December 31, 1948, Serial No. 68,761

Polyacrylonitrile possesses a number of prop erties which makes it valuable for many applications, such as, for example, for the formation f of fibers and films and other shaped articles. More specifically, fibers of polyacrylonitrile have good tensile strength but in other properties they are not entirely satisfactory. One deficiency of these fibers is their low receptivity to certain types of dyes. Because of this poor dye receptivity polyacrylonitrile fibers cannot be used for the preparation of fabrics having certain desired colors. This is a serious defect from a commercial standpoint.

This invention has as an object a new and useful composition of matter comprising a modified polyacrylonitrile. A further object is the production of solutions which upon extrusion into a coagulating bath yield improved shaped articles comprising a modified polyacrylonitrile. A further object is a shaped article, such as a film, filament or the like which comprises a modified polyacrylonitrile and which has excellent dye receptivity. Further objects reside in methods for obtaining these shaped articles.

I have found that the above objects can be accomplished and that the above-mentioned disadvantages of the prior practice can be overcome by means of a partially hydrolyzed polyacrylonitrile. The partially hydrolyzed poly-,- acrylonitriles of this invention can be obtained of the nitrile groups may be hydrolyzed further to carboxyl groups, but under preferred conditions the hydrolysis to carboxyl groups is insufilcient to impart to the product solubility in dilute alkali.

In a preferred manner of carrying out this invention, finely divided polyacrylonitrile is added to sulfuric, nitric or phosphoric acid of a concentration sufiicient to dissolve the polymer- The particular concentration of acid employed depends on the particular acid and par- "ticular temperature being used. Sulfuric acid by dissolving polyacrylonitrile in one of .thewellj' known -ic acids of nitrogen, phosphorus and sulfur, namely, nitric acid, phosphoric acid and sulfuric acid. The products obtained in' accordance with the practice of this invention consist of modified, coagulated polyacryloni The most desirable products are those trile, obtained by continuing the hydrolysis until at of 75% to 85% strength, i. e., 75% to 85% H2804 and 25% to 15% water, is preferred for dissolving polyacrylonitrile at temperatures between 10' and 25 C. Nitric acid of to strength is suitable for dissolving polyacrylonitrile at temperatures between 0 and 35 C. Phosphoric acid of approximately100% concentration dissolves polyacrylonitrile at temperatures of 0 to 35 C. The mixture of polyacrylonitrile and the inorganic oxy acid is stirred until a uniform solution is obtained. The nitrile groups in the polyacrylonitrile in solution are gradually hydrolyzed and converted to amide groups by the oxy acid, the rate of hydrolysis or} conversion depending primarily on such factors as the kind and concentration of the oxy acid and the temperature of hydrolysis. The resulting solution is held within the above-mentioned temperature ranges until the desired degree of conversion is obtained. When sulfuric acid of to, 30% strength is used, 2% to 75% conversion of nitrile groups to amide groups is obtainedinfito hours at 0 to 5 C. When .70 %,-nitric acidis employed, similar conversions areobtain'fedinfi to 100 hours'at '25 0. With .100,%1".lpliosphoric acid at 25 0. the rate of conversion approximately the same as with least 2% and not more than 75% of the nitrile groups originally present have been hydrolyzed,

nitric acidat-the same temperature. I from vthe standpoint'of c'oncentrationof solids at spinning viscosity, solutions .of polyacrylonitrile in nitric acid are especially suitable because nitric, acid and thereby converted primarily into amide groups.

' More specifically, the practice of this invention involves dissolving polyacrylonitrile in an acid of the above-mentioned kind and extruding the solution into a liquid coagulating bath which is a non-solvent for the dissolved polymer but a solvent for the acid, some water being present either in the acid solution of polyacrylonitrile or in the coagulating bath. Although the nitrile groups originally present are converted primarily into amide groups, a small number is-capab le of dissolving considerably'higher concentrationsof polyacrylonitrile than sulfuric or phosphoric acids. Phosphoric acid is the least desirablefof the three from this standpoint. The partially hydrolyzed polyacrylonitrile is isolated by extruding the oxy acid solution in the desired shape,e. g., in the form of films or fibers, into an aqueous coagulating bath at.

0'-60 C. Informing fibers,- those polymers in which from 25% to 65% of the nitrile groups are converted to amide groups are especially preferred since the resulting fibers have good receptivity to direct, vat, acetate, and acid type dyes. The coagulated films and fibers are then washed free of the salts and acid present, and dried. The resulting films or fibers can be sub- Jected to conventional aftertrea'tments such as drawing, or stretching, to develop optimum physical properties.

The polyacrylonitrile used in the practice of this invention can be prepared by any of the conventional methods for polymerizing acrylonitrile. Preferably the polymer is prepared by the to further drawing treatment in hot oil or hot air prior to evaluation. In one case the sized yarn is passed through mineral oil at 205 C. and drawn to 9 times its original length. Another sample of the sized yarn is passed through air at 215 C. and drawn to 12 times its original length. In a third sample the yarn is drawn to 12 times its original length-in air at 215 C., after which it is relaxed 17.5%. The properties of 10 these yarns are summarized in the following table:

Hot-drawn yarns of Example I Yarn Properties Tenacity/E1011 tion g. p. d./ Work Re- Method of Drawing l Shrinkage D e Race in Boiling ,33, ui m m Water, Elam: a acid and Dry Loop wet Per Cent (Per cent) direct dyes l3 2. 0/2 2. 6/23 52 8i Good.

Hot All 8.1/4. 6 4.1/23 82 Hot Air and Relaxed 3. 4/44 2. 8136 8. 2145 30 87 ammonium persulfate catalyzed polymerization 25 of acrylonitrile dissolved or emulsified in water. It can also be prepared by other polymerization reactions such as, for example, by the emulsion type polymerization reaction described in U. S. 2,160,054 to Bauer et al.

The invention is illustrated in further detail by the following examples in which the proportions of ingredients are expressed in parts by weight unless otherwise specified.

EXAMPLE I One hundred and ten parts of powdered polyacrylonitrile having a relative viscosity of 1.338 measured in 0.1% concentration (0.1 g. per 100 ml.) in dimethylformamide at 25 C. is stirred into 2,640 parts of 75% sulfuric acid maintained at -6 C. by means of an ice bath and stirring is continued until a uniform solution is obtained (about 18 hours). This solution is then stored at 2-3 C. and maintained under a pressure of hydrolysis of the mmle groups in the Dalila? -20 mm. of mercury to remove air bubbles. After the solution has aged for 48 hours from the time the polyacrylonitrile was first added to the sulfuric acid a portion amounting to 830 parts is extruded from a stainless steel bomb through a spinneret having 60 holes, each 0.003" in diameter, into a saturated aqueous solution of sodium acid sulfate at C. The pH of the coagulating bath is maintained between 2 and 4 by the periodic addition of sodium hydroxide solution during the spinning of the yarn. The polyacrylonitrile coagulates in the form of yarn in the sodium bisulfate bath. The yarn is then passed under tension through a boiling aqueous 20% solution of sodium sulfate to reduce gel swelling and to draw it. The yarn is drawn, or stretched, to 1.52 times its original length during passage through this hot sodium sulfate solution. The stretched yarn is wound on bobbins, washed in running water and dried at 20-30 C. The resulting yarn is colorless and glossy. Analysis of samples of the yarn for carbon, hydrogen, and nitrogen gives the following data: Found, N. 23.43%; C. 61.70%; H, 6.25%. The per cent hydrolysis of the nitrile groups to amide groups in the polymer calculated from nitrogen analysis is 37.5%.

The yarn from the above example is given a twist of 2 or 3 turns per inch, treated with a'conventional rayon viscose size, and then subjected All yarns previously drawn 1.52 times their original length in 20% aqueous sodium sulfate solution at The tenacity and work recovery properties of the yams described in this specification are determined by standard testing procedures for yarn. Shrinkage is determined by measuring a segment of the yarn before and after a 3-minute immersionin boiling water. Dye receptivity is determined qualitatively by immersing a sample of the yarn held taut on a wire form in a hot dye bath for one hour, followed by washing the sample in hot soap solution for 30 minutes. The

dye receptivity is judged by the amount of color retained by the yarn in comparison with, control samples of unhydrolyzed polyacrylonitrile yarn.

EXAMPLE II Another 830-part portion of the 75% sulfuric acid solution of polyacrylonitrile described in Example I is aged for 72 hours at 2-3 C. and spun into yarn by the procedure of that example.

. Analysis of this yarn gives the following results:

N, 21.75%; C, 58.12%; H, 6.60%. The per cent lonitrile calculated from nitrogen content is 63%. Yarn stretched 1.52% in the hot sodium sulfate bath, twisted and sized as in Example I, and then drawn to 9 times its original length in mineral oil at 205 C. exhibits the following properties:

Dry tenacity 2.3 g./denier at 3% elongation, loop tenacity 2.1 g./den.ier at 2% elongation, wet tenacity 2.0 g./denier at 36% elongation, 72% work recovery at elongation, shrinkage of 68% on immersion in boiling water, and good dye receptivity to both acid and direct dyes. EXAMPLE III Another 830-part portion of the sulfuric acid 50 solution of polyacrylonitrile of Example I is aged at 2-3 C. for a total of 96 hours and then spun into yarn in the same way as in the preceding two examples. Analysis of this yarn shows it to contain 21.15% nitrogen, 56.26% carbon, and

6.60% hydrogen. The degree of conversion of nitrile groups to amide groups calculated from nitrogen content is 73%. Yarn treated and drawn in exactly the same way as that of Example II has the following properties: Dry tenacity 3.0 g./denier at 13% elongation. loop tenacity 75 direct C1288.

EXAMPLE IV Fifty parts of polyacrylonitrile having a relative viscosity of 1.218 measured in 0.1% concentration (0.10 g. per 100 ml.) in dimethylformamide at 25 C. is dissolved in 950 parts of 76% sulfuric acid at 3-6 C. in the manner described in Example I. The resulting smooth solution is aged for a total of 24 hours at 3-6 C. and then spun into a saturated aqueous solution of sodium bisulfate at 20 C. by the procedure described in Example I with the exception that the yarn is drawn to 3.1 times its original length during passage through the hot sodium sulfate solution. Two washed, twisted, and sized samples of this yarn are subjected to a further drawing to 4 times and 6.4 times, respectively, the original length of the yarn in oil at 200 C. The physical properties of these yarns are summarized in the following table. Analysis of the yarn: Found C, 64.01%; H, 6.07%; N, 24.46%; 8. 0.045%. Calculated for one nitrile group out of five hydrolyzed to an amide group CH17N5OZ C, 63.6%; H, 6.00%; N, 24.7%.

Hot-drawn yams of Example IV Yarn Properties Work Recovery (From 34% Elongation), Per Cent Hot Oil Draw Tenacity/Elongation, g. p. d./

Ratio 1 Per Cent 1 All yarns previously drawn to 3.1 times their original length in boiling aqueous sodium sulfate during spinning.

EXAIVIPLE V A 5% solution of polyacrylonitrile in 76% sulfuric acid is prepared by stirring 40 parts of polyacrylonitrile having a relative viscosity of 1.218 measured in 0.10% solution (0.10 g. per 100 ml.) in dimethylformamide at C. into a mixture of 152 parts of water and 608 parts of. 95% sulfuric acid maintained at 345 C. by means of an ice bath. A clear, amber-colored solution is obtained in about 8 hours stirring. After storing at 3-5 C. for 12 hours more, the solution is spread on a glass plate which is then immersed in water at'room temperature. A good, tough film of partially hydrolyzed polyacrylonitrile, which can be handled without tearing, is formed.

EXAMPLE VI An aqueous solution of 1400 parts of 84% sulfuric acid is cooled with stirring in an ice-salt bath until the temperature of the resulting thick slurry of crystalline sulfuric acid monohydrate drops to 6 C. Simultaneously, a slurry of 96 parts of finely powdered polyacrylonitrile having a relative viscosity of 1.338 in 0.10% solution (0.10 g. per 100/ml.) in dimethylformamide at 25 C. in 904 parts of cold (-2 C.) 61% aqueous sulfuric acid is prepared. The polyacrylonitrile slurry is added rapidly to the stirred crystalline sulfuric acid monohydrate slurry, the temperature of the mixture rising quickly to 6 C. then falling to 4 C. within 3 minutes. The icesalt bath is replaced by an ice-water bath and the mixture maintained under reduced pressure at 03 C. with continued, slow stirring for two hours. The resulting clear viscous solution, which is practically free from air bubbles, is stored at atmospheric pressure in an ice bath for an additional 66 hours, whereupon it is spun into 60-filament yarn in a coagulating bath consisting of 40% aqueous sulfuric acid at 45 C. by the general procedure described in Example I. The resulting yarn, stretched to 1.3 times its original length during passage through boiling water, and subjected to the usual finishing and twisting treatments, can be drawn on a hot pin at 170 C. up to ten times its original length. The yarn stretched to 1.3 times its original length has a shrinkage of 26-42% in hot water. The nitrogen content of this yarn, 24.58 (determined by Kjeldahl analysis), indicates the polyacrylonitrile to be 21.5% hydrolyzed.

EXAMPLE VII A solution of polyacrylonitrile innitric acid is prepared by thoroughly agitating a mixture of 6.8 parts of polyacrylonitrile and 68.5 parts of concentrated nitric acid (70% HNOa minimum) at room temperature (about 25 C.). After the polymer is completely in solution agitation is continued for one hour and the solution is allowed to stand at 25 C. for 15 hours. The solution is then slowly poured in a fine stream into hot water which i kept rotating in a container to prevent the freshly formed thread from sticking to itself while it is still sticky. On removal from the water, the thread of partially hydrolyzed polyacrylonitrile is observed to be clear, of good color, elastic, tough, and capable of being colddrawn. After drying under tension in the open air the filament is clear, of good color and fairly tough.

Two phenomena appear to operate when polyacrylonitrile is dissolved in nitric, phosphoric or sulfuric acid: (a) direct solution, and (b) partial hydrolysis. These phenomena are inseparable, but under some conditions one will predominate, while under different conditions the other will predominate. The kind and concentration of the acid and the operating temperature determine which of these phenomena will predominate at a given stage of the reaction, and, together with the time of treatment, will control the degree of hydrolysis of the nitrile groups. When sulfuric acid of to 100% strength, i. e., 75% to 100% H2804 and 25% to 0% water, is employed at temperatures of 10 to 50 C., the acid apparently acts first as a solvent for the unmodified polyacrylonitrile, and-then gradually hydrolyzes the nitrile groups in the dissolved polymer. Nitric acid of 55 to 70% strength used at temperatures of 0 to 25 C. and 100% phosphoric acid used at the same temperatures acts in a similar manner. On the other hand, when sulfuric acid of 50% to 75% strength is employed at elevated temperatures, e. g., 60 to C., the acid apparently first hydrolyzes the nitrile groups near the surface of the polymer and then dissolves the polymer, the partially hydrolyzed polymer being soluble in sulfuric acid of lower strength than required for unmodified polyacrylonitrile. Nitric acid of 50% strength and lower and phosphoric acid of 90% strength and lower act in a similar manner. Thus, the acids of lower concentrations. e. g., sulfuric acid of 50 to 75% concentration, nitric acid of 40 to 50% concentration and phosphoric acid of 75 to concentration, can be used to dissolve polyacrylonitrile which has previously been partially hydrolyzed. The rather drastic condiitons required to dissolve polyacrylonitrile in the oxy acids of lower concentrations mentioned above tend to cause hydrolysis of the nitrile groups beyond amide groups to imide groups and even to carboxyl groups as evidenced by the fact that polymers obtained in this manher are soluble in dilute aqueous alkali but are insoluble in water. When sulfuric acid solutions of polyacrylonitrile are to be held at low temperatures, e. g'., at to C., it is preferable to use sulfuric acid of 75% to 80% concentration as the solvent since sulfuric acid monohydrate, H2SO4.H2O, which has a melting point of 8.6" C., may tend to crystallize from acid of more than 80% strength at these temperatures. Sulfuric acid containing excess sulfur trioxide will dissolve polyacrylonitrile, but the use of such strong acid is undesirable since it causes some charring of the dissolved polymer.

when water is not present in the solvent acid or is present in only small amounts, it should be contained in the coagulating bath in amount sufficient to make the bath a non-solvent for the dissolved polymer. For instance the coagulating bath for sulfuric acid solutions of polyacrylonitrile should contain about 60% water or more.

In the practice of this invention on a commercial scale, it is preferable, for economic reasons, to use as solvent for the polyacrylonitrile an acid of the lowest concentration possible since in the formation of films or fibers the polyacrylonitrile/inorganic oxy acid solution is extruded into aqueous baths, and obviously the higher the concentration of the acid in the solution the greater will be the amount of acid to be recovered from the coagulating bath. Therefore, in order to reduce to the minimum the amount of acid necessary to recover, the unmodified polyacrylonitrile can be dissolved at high solids concentration in, for example, sulf-uric acid of concentrations of 75% or above and then, after hydrolysis has proceeded to a substantial extent, the solution diluted, for example, to a sulfuric acid content of as low as 60% in some instances, thus reducing the polymer solution viscosity sufliciently to' allow it to be extruded.

The coagulation of the sulfuric, nitric or phosphoric acid solutions of polyacrylonitrile of this invention can be carried out in a variety of ways. As indicated previously, coagulation is preferably carried out by extruding the acid solution into aqueous baths. Such baths include water alone; aqueous solutions of salts such as, for example, sodium sulfate, sodium acid sulfate, sodium nitrate, sodium dihydrogen phosphate, and ammonium sulfate, in concentration up to the saturation point of the salt in. water at the temperature at which the bath is being used; anddilute sulfuric, nitric and phosphoric acid, e. g., aqueous acid of 5%-40% concentration. Coagulating baths in which the pH is maintained between 2 and 4 by the addition of sodium hydroxide during coagulation of the oxy acid solution give good results. The use of alkaline baths is to be avoided because of the tendency of alkaline ma- 8 polyacrylonitriie solutions in aqueous oxy acids containing sufficient water to inhibit undesirable chemical reaction of the acid with the organic liquid. Preferably these organic non-solvent liq-- uid baths are used to coagulate poiyacrylonitrile solutions in sulfuric acid of 60% to 80% strength or lower, in those cases where a high proportion of the nitrile groups have been hydrolyzed to amide groups. 4

The partially hydrolyzed polyacrylonitrile can be isolated or coagulated in any desired form, such as, for example, fibers, monofllaments, ribbons, films, sheets, etc. by conventional means for forming such shaped articles. Thus, as illustrated by the examples, fibers or yarns can be obtained by extruding the solution through spinnerets having the desired number and size of openings into the coagulating bath, and films or ribbons can be obtained by extruding the terials to cause color formation in the coagulated polymer. While aqueous baths are preferred, for economic reasons, for the coagulation of the partially hydrolyzed polyacrylonitrile other liquids which are miscible with aqueous sulfuric, nitric or phosphoric acids but which are non-solvents for the dissolved polymer can also be employed for this purpose. Examples of such non-aqueous liquids which are suitable include organic liquids of the following types: ethers, e. g., diethyl ether; lower aliphatic alcohols, e. g., methyl, ethyl and butyl alcohols; and ketones, e; g., acetone. These non-aqueous liquids are employed in coagulating sulfuric acid solution of the hydrolyzed p acrylonitrile onto a flat support followed by immersing the support and film in a suitable coagulating bath or by directly extruding the solu.-.

tion in sheet or in ribbon form into the coagulating bath. Furthermore, if a granular product is desired the oxy acid solution can be coagulated in the non-solvent bath with sufficient agitation to form particles of the desired size, and to keep the coagulated particles of the polymer from coalescing.

The shaped articles of this invention, i. e., films, filaments, etc, of partially hydrolyzed polyacrylonitrile may, if desired, contain modifying agents such as, for example, dyes, pigments, plasticizers, fillers, and the like. However, in such cases the modifying agents are present only in minor proportions.

The yarn, fibers or films of hydrolyzed polyacrylonitrile obtained by the coagulation of the oxy acid solutions of this invention can be subjected to conventional aftertreatments to improve the physical or other properties of such shaped articles. For example, the tensile strength of yarn is improved by drawing or stretching the wet spun yarn. Yarns of the partially hydrolyzed polyacrylonitriles of this in-' vention, can be drawn or stretched to about 9 times their original length in the coagulating bath or in hot aqueous solutions of salts such as sodium sulfate. They can also-be drawn up to 12 times their original length by stretching them while heated to a temperature of about 200-220 C. in air or in mineral oil at 200--21 0 C... or on a metallic pin heated to to 210 C. In general, optimum balance of properties is obtained by subjecting the yarn to a hot drawing treatment followed by a relaxing. treatment, e. g., a relaxation of 10-20% of the max;- imum drawn length.

These partially hydrolyzed polyacrylonitrile yarns have different degrees of water sensitivity depending on the degree of conversion of nitrile groups to amide groups, the greater the degree of conversion the greater bein the water sensitivity. While yarns of hydrolyzed polyacrylonitrile of 25-65% conversion are preferred because of their good dye receptivity, such yarns may be too sensitive to hot water for some applications. In such case the yarns can be subjected to an aftertreatment such as, for example,

with formaldehyde to improve their water resisttension, can be immersed in a solution of 2% formaldehyde, 10% sulfuric acid and 30% sodium sulfate for 24 hours at 25 C. and then heated for 1 hour at 70 C. in fixed lengths in the bath. After washing and drying, yarns treated in this manner generally shrink less than on immersion in boiling water for 3 minutes.

The partially hydrolyzed polyacrylonitriles of this invention isolated from the sulfuric, nitric or phosphoric acid solutions can, if desired, be redissolved in other solvents and formed into shaped objects. e. g., films and fibers, by conventional means. The properties of a film of partially hydrolyzed polyacrylonitrile (34% conversion of nitrile groups to amide groups in sulfuric acid solution) cast from dimethylformamide solution are summarized below. For purpose of comparison, the properties of a film of the original polyacrylonitrile of the same thickness (2-3 mils) and cast from the same solvent are also given.

Partially fllydriolgiglinal yre o y- Property Polyacryloniacrylonitrile trile Water absorption (immersion in water 24 hours at 25 C. -.per cent 14.05 1. 85 Tear resistance (modified Elmendori test):

25 0., 50% R. H 10. 9 4.85 25 0., wet ..g 339+ 10. 5 Flexibility (number of flexes in Pfund Flexor):

25 o R. H 3 1 25 0., wet 182 30 Tensile strength, 25 0., 50% R. H ]b./sq. in.. 11, 000 8,300 Stiffness (A. B. T. M. method D747-43T):

25 0., 50% R. H lb./sq. in" 465, 000 545, 000 25 0., wet ..lb./sq. in 77,800 365,

The sulfuric acid solutions of partially hydrolyzed poLvacrylonitrile described herein are particularly useful for the preparation of fibers and films. Furthermore, fibers of partially hydrolyzed polyacrylonitrile in which from 25-65% of the nitrile groups are converted to amide groups are especially suitable for the preparation of fabric to be dyed because of the good dye receptivity of these particular partially hydrolyzed polyacrylonitrile fibers.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Iclaim:

1. A composition of matter comprising polyacrylonitrile in which from 25% to 65% of the nitrile groups are converted to amide groups.

2. A shaped article in the form of a filament comprising poLvacrylonitrile in which from 25% to 65% of the nitrile groups are converted to amide groups.

3. A process for obtaining shaped articles which comprises the steps of dissolving at a temperature of -10 C. to 35 C. polyacrylonitrile in an oxy acid from the group consisting of nitric acid, phosphoric acid, and sulphuric acid, maintaining the solution at said temperature until from 2% to 75% of the nitrile groups in the polyacrylonitrile have been converted into amide groups, extruding the solution thus obtainedinto a liquid coagulating bath which is a nonsolvent for the dissolved polymer but which is a solvent for said acid, water being present in at least one of these two steps.

4. A process which comprises dissolving at a temperature of from 0' C. to 35 C., polyacrylonitrile in aqueous nitric acid containing from to 70% HNOa, maintaining the solution at said temperature until from 2% to 75% of the nitrile groups in the polyacrylonitrile have been converted into amide groups, and then extruding the solution thus obtained into a liquid coagulating bath which is a nonsolvent for the dissolved polymer but which is a solvent for nitric acid.

5. The process set forth in claim 4 in which said coagulating bath is an aqueous liquid coagulating bath.

6. The process set forth in claim 4 in which said solution is maintained at said temperature until from 25% to of said nitrile groups are converted into amide groups.

7. The process set forth in, claim 6 in which said coagulating bath is an aqueous liquid coagulating bath.

8. A composition of matter comprising a solution in nitric acid of polyacrylonitrile in which from 25% to 65% of the nitrile groups are c0nverted into amide groups.

9. A composition of matter comprising a solution in aqueous nitric acid containing from 55% to HNOa, of polyacrylonitrile in which from 25% to 65% of the nitrile groups are converted into amide groups.

' ALLEN E. POLSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Rubber Chemistry andlechnology, vol. 17.

00 April 1944, page 358. COPY in Division 50.

Claims (1)

1. 3. A PROCESS FOR OBTAINING SHAPED ARTICLES WHICH COMPRISES THE STEPS OF DISSOLVING AT A TEMPERATURE OF -10* C. TO 35* C. POLYACRYLONITRILE IN AN OXY ACID FROM THE GROUP CONSISTING OF NITRIC ACID, PHOSPHORIC ACID, AND SULPHURIC ACID, MAINTAINING THE SOLUTION AT SAID TEMPERATURE UNTIL FROM 2% TO 75% OF THE NITRILE GROUPS IN THE POLYACRYLONITRILE HAVE BEEN CONVERTED INTO AMIDE GROUPS, EDTRUDING THE SOLUTION THUS OBTAINED INTO A LIQUID COAGULATING BATH WHICH IS A NONOSOLVENT FOR THE DISSOLVED POLYMER BUT WHICH IS A SOLVENT FOR SAID ACID, WATER BEING PRESENT IN AT LEAST ONE OF THESE TWO STEPS.