Process for preparing an acrylonitrile polymer

Abstract: An acrylonitrile polymer having an intrinsic viscosity in the range of 0.5 to 1.4 and a sulfonic acid end group content of about 0.20 to 0.35 weight percent is obtained by polymerizing acrylonitrile and one or more monomers free of acid dyesite groups in the presence of a redox system containing an oxidizing agent, a reducing agent, and a copper activator, the reducing agent being a mix­ ture of a bisulfite and a mercapto compound in propor­ tions which give the desired end group content whereby intrinsic viscosity can be varied independently.

Description: POLYMERIZATION PROCESS AND PRODUCT This invention relates to an acrylonitrile polymer having a limited range of intrinsic viscosity and a consistent level of sulfonic acid end groups throughout said intrinsic viscosity range and to a process for obtaining same. More particularly, this invention relates to such a polymer useful in the spinning of acrylonitrile polymer fiber having a consistent level of dyesites furnished by sulfonic acid end groups derived from a bisulfite com- pound used as a redox catalyst component during polymerization, the dyesite level being the same at the various levels of intrinsic viscosity contemplated. In the spinning of acrylonitrile polymer fiber, it is desirable to employ as the fiber-forming polymer an acrylonitrile polymer having dyesites incorporated in the polymer structure. A particlularly desirable procedure for introducing such dyesites in the polymer structure is to conduct polymerization by means of a redox catalyst system in which a bisulfite compound is used as reducing component. In this manner, chain ends of the polymer will contain sulfonic acid groups derived from the bisulfite com- pound employed in the redox system. However, in this polymerization procedure, molecular weight as indicated by intrinsic viscosity, is also controlled by the redox system employed. Lower molecular weight polymers are obtained from increased use of redox system with the result that more sulfonic acid groups are introduced as end group components in the lower molecular weight polymers. When these sulfonic acid end groups are used as the dyesites in fiber prepared from the acrylonitrile poly mer only a certain number are required to provide the desired range of dyeability for textile applications. This range is about 0.2 to 0.35 weight percent of sulfonic acid end groups based on the weight of the polymer. Lower contents of sulfonic acid end groups do not provide an adequate range of dyeability for textile uses. Higher contents of sulfonic acid end groups are not necessary for the full range of dyeability desired for textile purposes and can cause very rapid uptake of dye from-the dyebath with the result that level dyeings are not achieved. In U.S. Patent 2,974,123, issued March 7, 1961 to Ketterer (duPont), it is disclosed that color-stable acrylonitrile polymers of intrinsic viscosity in the range of 1.30 to 2.20 can be obtained by polymerizing the monomer content in aqueous medium in proportions as follows: Percent total monomers 18.5 to 35 P.p.m. ionic iron 0.2 to 5 Percentl beta-mercaptoethanol O.05 to 0.3 Percent1 activator as sodium metabisulfite2 0.2 to 3.8 Percent1 catalvst as potassium persulfate 0.2 to 0.7 Temperature (OC.) 45 to 60 Residence Time (min.) 30 to 110 Water to balance acidified with sulfuric acid to pH of -1.8 to 3.75 Based on monomers. 2 Stoichiometric equivalent amounts of S02 may be substituted for sodium meta-bisulfite. If SO is used, no acid is necessary for lowering pH. The reference teaches use of monomers containing sulfonic acid groups and both high and low levels of activator to catalyst. There is no teaching that the content of sulfonic acid end group derived from the bisulfite activator can be maintained constant while varying the intrinsic viscosity of the polymer. Accordingly, there exists the need for a process for polymerizing an acrylonitrile polymer free of comonomers containing acid dyesite groups in the presence of a redox catalyst system employing a bisulfite as the reducinc agent whereby the content of end groups derived from the bisulfite is controlled while the intrinsic viscosity of the polymer can be caried independently. The provisibn for such a process and polymer would fulfill a long-felt need and constitute a significant advance. In accordance with the product aspect of the present invention, there is provided an acrylonitrile polymer comprising at least about 85 weight percent acrylonitrile, the balance being one or more ethylenically unsaturated monomers copolymerizable with acrylonitrile and being free of acid dyesite groups, said polymer having an intrinsic viscosity in the range of about 0.5 to about 1.4 and a sulfonic acid end group content in the range of about 0.2 to about 0.35 weight percent. In accordance with the process aspect of the present invention, there is provided a process for preparing an acrylonitrile polymer which comprises forming at a temperature in the range of about 400C. to about 800C., a suspension comprising a monomer content of at least 85 weight percent acrylonitrile, the balance being one or more methyl enically unsaturated monomers free of acid dyesite groups, said monomer content forming from about 25 to about 40 percent based on the weight of said suspension, initiating polymerization by adding to said suspension effective amounts of a redox system comprising an oxidizing agent, a reducing agent, and a copper activator, said reducing agent comprising a mixture of a bisulfite and a mercapto compound the relative proportions of said bisulfite and said mercapto compound being such as to provide a sulfonic acid end group content in the resulting polymer in the range of about 0.2 to about 0.35 weight percent, based on the weight of polymer, and to provide a polymer having an intrinsic viscosity in the range of about 0.5 to 1.4, termiating said reaction at a monomer conversion in the range of about 75% to about 90%, and recovering the polymer thus produced. The process of the present invention enables acrylonitrile polymers free of comonomers containing acid dyesite groups to be prepared withing the range of intrin sic viscosities specified at consistent levels of sulfonic acid end group content as desired. Any specific content of sulfonic acid end groups within the range specified can be obtained in the acrylonitrile polymer at any intrinsic viscosity value within the range stated. This enables these rather low molecular weight acrylonitrile polymers (as indicated by intrinsic viscosity) to be prepared at desirable levels of dyesites sulfonic acid end groups) instead of the excessive levels previously obtained. As a result, fiber prepared from the polymers of the invention have desirable dyeing characteristics without the rapid dye uptake-associated with high dyesite contents. 'An important feature of the present invention is that it enables intrinsic viscosity of the resulting polymer to be controlled independently of the content of sulonic acid end groups therein. The sole figure of drawing shows the relationship between sulfonic acid end groups and intrinsic viscosity of the polymer for polymers produced -in accordance with the present invention and those produced in accordance with those of the prior art. In preparing the polymer of the present invention, continuous suspension polymerization may be employed. As indicated, the content of acrylonitrile in the polymer will be at least about 85 weight percent with any balance com- prising one or more monomers free of acid dyesite groups. Comonomers suitable for use in the present invention include, for example, methyl acrylate, ethyl acrylate, butyl acrylate, methoxymethy 1 acrylate, beta-chloroethyl acrylate, and the corresponding esters of methacrylic acid and chloroacrylic acid, vinyl chloride, vinyl fluoride, vinyl bromide, yinylidene chloride, vinylidene bromide, allyl chloride, l-chloro-l-bronioethylene, methacrylonitrile, methyl vinyl ketone, vinyl formate, vinyl acetate, vinyl propionate, vinyl stearate, vinyl benzoate, N-vinyl-carbazole, vinyl furan, alkyl vinyl ethers, dimethyl citraconate, diethylmesaconate, styrene, dibromostyrene, vinyl napthalene, 2-methyl -1 -vinylimidazole, 4-methyl -1-vinyl- imidazole, 5-methyl-1-vinylimidazole, acrylamide, methacrylamide, dimethyl-acrylamide, isopropyl acrylamide, allyl alcohol, 2--vinylpyrid:ne, 4-vinylpyridine, 2-methyl-vinylpyridine, vinylpyrrolidone, vinylpiperidone, 1,2-dihydroxypropyk methacrylate , hydroxyethyl methacrylate l-trimethyl ammonium-2 -hydroxypropy 1 methacrylate methosul fate, and the like. The monomer content should comprise about 25 to 40 weight percent of the aqueous reaction mixture. The reaction mixture is catalyzed with a suitable quantity of redox catalyst system to provide the desired molecular weight value and sulfonic acid end groups. Suitable oxidizing agents for the redox catalyst systam include, for example, potassium persufate, potassium chlorate, potassium perchlorate, potassium peroxide and the like as well as the corresponding sodium and ammonium salts and hydrogen peroxide. The reducing component of the useful redox system is a mixture of two components, a bisulfate and a mercapto compound such as mercaptoethanol. The bisulfite may be potassium, sodium, or ammonium bisulfite or the corresponding metabisulfite in an amount which is sufficient to provide from about 0.2 to about 0.35, preferable about 0.25 to 0.30 weight percent sulfonic acid end groups. A mercapto compound is employed in amounts necessary to complete the polymerization reaction and will be in the range of about 0.4 to 0.8 weight percent based on the weight of monomers. As metal activator, it is desirable to employ copper sulfate pentahydrate. This compound has advantage in that it does not discolor the polymer or fiber prepared therefrom to the same extent as does iron. The redox system is generally used in amounts of about 4 to about 20 parts of oxidizing component per 1000 parts of monomer content of the aqueous reaction mixture and the amount of reducing agent will be consistent with amount of oxidizing component employed. The reaction mixture is heated to a temperature of about 40 to 800C. and the reaction is initiated by addition of the redox system as described. The reaction is allowed to continue until a conversion in the range of about 75 to 90% is obtained. The degree of conversion is readily determined by analysis. The reaction is terminated by destroying the reducing agents by addition of a suitable shortstop agent to the reaction mixture. After the reaction is terminated as indicated, the polymer is recovered from the reaction mixture and unreacted monomer is distilled from the reaction medium. the invention is more fully illustrated in the examples which follow wherein all parts and percentages are by weight unless otherwise specified. In the examples, intrinsic viscosity is given. This value is measured in dimethyl forinamide at 400C. COMPARATIVE EXAMPLE A To a well-agitated suitable cylindrical vessel there were added a monomer content of 0.2% methyl methacrylate and 90.8% acrylonitrile with water and various additives to produce the composition shown in the following table which also gives the reaction conditions and other details. The additions were made continuously and overflow from the reactor had the properties indicated. Polymer was recovered from the overflow as a crumb and had the properties given in the table. Following the above procedure, an addition series of runs were made except that in individual runs the amount of redox catalyst system employed was increased to provide polymer of reduced intrinsic viscosity. Intrinsic viscosity and sulfonic acid end group content determined on the recovered polymer crumb form the basis for the plot in the accompanying drawing labelled "Prior Art Redox Systems". Examples 1 - 4 Following the procedure of Comparative Example A, additional polymers were prepared in accordance with- the present invention. All details, as regarding Comparative Example A, are also given in the table. EXAMPLE COMPARATIVE A 1 2 3 4 POLYMERIZATION CONDITIONS 30 35 35 35 35 MONOMER CONCERNTRATION (%) REDOX SYSTEM %NaClO3 0.32 0.70 - - 0.53 %K2S2O8 - - 1.4 1.4 %ss-Mercaptoethanol - 0.64 0.65 0.5 0.48 %CuSO4#5H2O - 0.003 0.0015 0.0015 0.0025 %NaNO3 2.27 0.35 - - 0.40 RESIDENCE TIME (MINUTES) 57 54 54 54 54 TEMPERATURE ( C) 50 55 60 60 60 REACTOR OVERFLOW (STEADY STATE) CONVERSION(%) 80.0 85.8 84.0 86.5 83.6 INTRINSIC VISCOSITY 1.5 1.01 0.98 1.10 1.2 pH 2.4 2.1 2.5 2.5 2.2 POLYMER CRUMB %METHYL METHACRYLATE 10.7 10.4 10.7 10.6 10.8 %ACRYLONITRILE 89.3 89.6 89.3 89.4 89.2 %-SO3H 0.30 0.25 0.27 0.27 0.25 From the data given in the tavle, it can be seen that in accordance with the present invention, the molecular weight of the polymer can be varied widely while maintaining the sulfonic acid end group content at an essentially constant level. Examples 5 & 6 The procedure of Example 1 is followed except that the methyl methacrylate is replaced by an equivalent amount of (5) methyl acrylate and (6) vinyl acetate, respectively. In each instance, similar results are achieved. In the sole figure of drawing, the sulfonic acid end group content is plotted against the intrinsic viscosity of the acrylonitrile polymers produced by prior art use of redox systems and that of the present invention. The figure shows that polymer of the instant invention has an essentially uniform sulfonic acid group content over a wide range of intrinsic viscosities while the prior art polymers have markedly increased sulfonic acid group content as the intrinsic viscosity weight is decreased.

Claims: WE CLAIM: 1. An acrylonitrile polymer containing repeating units comprising at least about 85 weight percent of acrylonitrile the balance being one or more ethylenically unsaturated monomers copolymerizable with acrylonitrile and being free from acid dyesite groups, said polymer having an intrinsic viscosity in the range of about 0.5 to about 1.4 and a sulfonic acid end group content in the rance of about 0.2 to about 0.35 weight percent. 2. The polymer of Claim 1 comprising repeating units of acrylonitrile and methyl methacrylate. 3. The polymer of Claim 1 comprising repeating units of acrylonitrile and methyl acrylate. 4. The polymer of Claim 1 comprising repeating units of acrylonitrile and vinyl acetate. 5. The polymer of Claim 1 wherein said sulfonic acid end group content is about 0.25 to about 0.30 weight percent. 6. A process for preparing an acrylonitrile polymer which comprises forming, at a temperature in the range of about 400C. to about 800C., a suspension of a monomer content comprising at least 85 weight percent acrylonitrile, the balance being one or more ethylenically unsaturated monomers free of acid dyesite groups, said monomer content forming from about 25 to about 40 weight percent, based on the weight of said suspension, initiating polymerization by adding to said suspension effective amounts of a redox system comprising an oxidizing agent, a reducing agent, and a copper activator, said reducing agent comprising a mixture of a bisulfite and a mercapto compound, the relative proportions of said bisulfite and said mercapto compound being such as to provide a sulfonic acid end group content in the resulting polymer in the range of about 0.20 to about 0.35 weight percent, based on the weight of the polymer, and to provide a polymer having an intrinsic viscosity in the range of about 0.5 to about 1.4, terminating said reaction at a monomer conversion in the range of about 75% to about 90%, and recovering the polymer thus produced. 7. The process of Claim 6 wherein said monomer content comprises acrylonitrile and methyl methacrylate. 8. The process of Claim 6 wherein said monomer content comprises acrylonitrile and methyl acrylate. 9. The process of Claim 6 wherein said monomer content comprises acrylonitrile and vinyl acetate. 10. The process of Claim 6 wherein the relative proportions of said bisulfite and said mercapto compound provide a sulfonic acid end group content of about 0.25 to about 0.30 weight percent.

Inventors: DAFTARY, SHASHIKUMAR H., KOURTZ, RAYMOND E.
Applicants: AMERICAN CYANAMID COMPANY
Application year: 1980
Main classification: C08F20
IPC codes: C08F4, D01F6, C08F20, C08F220