Abstract: The invention relates to filaments and fibers of acrylonitrile polymers, which contain 10 to 30% by weight of carboxyl groups, their use and processes for their production. The filaments and fibers exhibit, in the dry state, tensile strengths of more than 10 cN/tex and knot strengths of more than 6 cN/tex and can be processed on customary machinery and are suitable for the production of shaped structures of high water retention. The polymeric raw materials required for the spinning are produced by hydrolysis of acrylonitrile polymers using aqueous dilute acids in a heterogeneous phase system.

Abstract: An acrylonitrile polymer film is disclosed which film comprising a polymer containing higher than 80% by weight of acrylonitrile units, having higher than 300,000 of weight average molecular weight, and having molar fraction Ne for the segment of polymerization initiator bonded to the terminal of the polymer satisfying the following equation:Mw.times.Ne.ltoreq.

Abstract: The present invention provides crosslinked ampholytic copolymers that are highly absorbent to aqueous electrolyte solutions.

Abstract: A method of preventing polymer scale deposition in a polymerization vessel during polymerization of a monomer having an ethylenically double bond, wherein said polymerization is carried out in a polymerization of which the inner wall has been previously coated with a coating solution comprising:(A) an aromatic amine-based condensate,(B) at least one member selected from the group consisting of alkali metal salts and ammonium salts of a sulfonation product prepared by sulfonation of an aromatic amine-based condensate, and(C) at least one member selected from the group consisting of metal compounds, inorganic colloids, dyes and pigments; a scale preventive agent comprising the components (A), (B) and (C); and a polymerization vessel having a coating comprising the scale preventive agent. According the method, polymer scale deposition on the inner wall, etc. of the polymerization vessel can be effectively prevented.

Abstract: Vinyl polymers, e.g., the homo- and copolyvinyl chlorides, are prepared in one or more stages, to a degree of conversion of at least 50%, by suspended emulsion polymerizing at least one vinyl monomer, e.g., vinyl chloride, said at least one monomer having dispersed therein finely divided droplets of an aqueous solution of at least one component of a polymerization initiating system, and wherein the amount of water in said aqueous solution constitutes at least 19%, and preferably at least 20% by weight of the at least one monomer.

Abstract: A diagnostic test composition for detecting and measuring an analyte possessing biologic activity, the composition comprising(a) A redox catalyst system capable of converting a monomer to a polymer, the monomer capable of undergoing addition polymerization, the redox catalyst system comprising one or more chemical moieties with1) the analyte comprising at least one such moiety or2) in the case that the analyte lacks a redox catalyst property, the analyte is linked by a specific ligand to at least one such moiety or is linked by the specific ligand to a generator of at least one such moiety, and(b) at least one monomer capable of undergoing addition polymerization.

Abstract: A diagnostic test composition for detecting and measuring an analyte possessing biologic activity comprising(a) a photocatalyst system capable of converting a monomer to a polymer upon exposure to light, the monomer capable of undergoing addition polymerization, the photocatalyst system comprising one or more chemical moieties, with(1) the analyte comprising at least one such moiety or generating at least one such moiety or(2) in the case that the analyte lacks a photocatalyst property, the analyte is linked by a specific ligand to at least one such moiety or is linked by the specific ligand to a generator of at least one such moiety and(b) at least one monomer capable of undergoing addition polymerization.

Abstract: Group Transfer Polymerization (GTP) process for preparing a "living" polymer, the process comprising contacting under polymerizing conditions in a polymerization medium, at least one acrylic or maleimide monomer with an initiator which is a tetracoordinate organosilicon, organotin or organogermanium compound having at least one GTP initiating site and a catalyst which is or is a source of an anion selected from the group consisting of bifluoride, fluoride, cyanide, azide or a selected oxyanion, or a selected Lewis acid or Lewis base, the process further characterized in that the initiator or the anion or Lewis acid catalyst is chemically attached (grafted) to a solid support that is insoluble in the polymerization medium.

Abstract: Acrylic fibers with high physical properties particularly suitable as material for cement reinforcement are provided by spinning a spinning solution of an acrylonitrile polymer at a particular linear velocity ratio of extrusion, thereby forming gel fibers; regulating the internal water content of the gel fibers, subjecting the fibers to dry-heat treatment under tension or dry-heat stretching under a particular temperature condition; and cooling the fibers under tension.

Abstract: Group Transfer Polymerization (GTP) process for preparing a "living" polymer, the process comprising contacting under polymerizing conditions in a polymerization medium, at least one acrylic or maleimide monomer with an initiator which is a tetracoordinate organosilicon, organotin or organogermanium compound having at least one GTP initiating site and a catalyst which is or is a source of an anion selected from the group consisting of bifluoride, fluoride, cyanide, azide or a selected oxyanion, or a selected Lewis acid or Lewis base, the process further characterized in that the initiator or the anion or Lewis acid catalyst is chemically attached (grafted) to a solid support that is insoluble in the polymerization medium.

Abstract: Acrylic fibers of extremely short length suitable as a matting agent for paint, etc. The fibers are produced from a polymer containing more than 50 weight % acrylonitrile, the fiber diameter is less than 100.mu. and the fiber length is less than 3 mm.

Abstract: A process for preparing carbon fibers of high strength which includes the steps of homopolymerizing acrylonitrile or copolymerizing acrylonitrile with other vinyl monomers in a concentrated zinc chloride aqeuous solution containing 0.01-5% by weight of hydrogen chloride to form a polymeric solution which is spinned to form precursor filaments which are carbonized to provide carbon fibers.

Abstract: A highly shrinkable acrylic filament yarn which exhibits a degree of shrinking of at least 20% in boiling water, a maximum heat shrinking stress of at least 0.15 g/d in a dry heating atmosphere, and a Young's modulus of at least 280 Kg/mm.sup.2 after free shrinking treatment in boiling water.

Abstract: High tenacity acrylonitrile fibers are provided.The high tenacity acrylonitrile fibers comprise acrylonitrile polymers composed mainly of acrylonitrile having an intrinsic viscosity of at least 2.5 to 3.5 and having a degree of crystalline orientation measured by wide-angle X-ray diffraction within a range of 93-97%, a tensile strength of at least 10 g/d, an initial modulus of at least 180 g/d, a knot strength of 2.2 g/d and a surface smoothness.A process for production of the high tenacity acrylonitrile fiber which comprises once extruding an acrylonitrile polymer solution having an intrinsic viscosity of 2.5 to 3.5 in air or in an inert gas through a spinning nozzle, then introducing into a coagulating bath, subjecting the resulting coagulated filaments to washing with water, drawing and drying, and then drawing the filaments under a drawing tension of about 1.0 to 2.5 g/d with dry heating at about 160.degree. to about 250.degree. C.

Abstract: The present invention relates to a process and an apparatus for the continuous production of polymers and copolymers of water-soluble monomers particularly arcylic acid and/or methacrylic acid, optionally with additional comonomers, by the polymerization of an aqueous monomer solution that is introduced into the trough that is formed by an endless conveyor belt. The trough-like shape of the conveyor belt changes continuously into an extended flat profile during the polymerization process; starting from the side edges and working towards the center of the trough formed by the conveyor belt, the resulting polymer gel strand is released continuously during the transition of the curved trough-like shape of the conveyor belt into the extended, flat form.

Abstract: A mixture of an isomer of 2,2'-azobis(2,4-dimethylvaleronitrile) having a low melting point in an amount of about 70% by weight or more and an isomer of 2,2'-azobis(2,4-dimethylvaleronitrile) having a high melting point in an amount of about 30% by weight or less shows excellent solvent solubility, which is higher than that of the isomer having a low melting point. The mixture is useful as a polymerization initiator, and also as a blowing agent.

Abstract: A polymerization process which comprises contacting at least one polar acrylic type or maleimide monomer under polymerization conditions with (i) a tetracoordinate organosilicon, organotin or organogermanium initiator having at least one initiating site, (ii) a co-catalyst which is a source of fluoride, bifluoride, cyanide or azide ions or a Lewis acid, and (iii) from 0.1 to 10% by weight, based on the weight of monomer, of acetonitrile.

Abstract: An insoluble infusible electroconductive polymer is provided, which is derived from an organic compound having 3 to 6 carbon atoms and having a cyano group and an ethylenically or acetylenically unsaturated bond by mutually reacting this compound at an elevated temperature.

Abstract: Water-in-oil emulsions of monomers which form water-soluble polymers are polymerized in the presence of a biphase initiator system containing both an oil-soluble initiator and a water-soluble initiator or activator or alternatively a water-soluble initiator and an oil-soluble activator which results in polymers having improved performance characteristics. In addition, the system permits the satisfactory polymerization of monomers which could not have been reproducibly polymerized.

Abstract: Monofils and bristles which comprise at least 90% by weight of acrylonitrile units and have a linear density of more than 2.5 tex possess a relative solution viscosity of 1.7 to 6.0, a tear strength of at least 20 cN/tex and an initial modulus of more than 700 cN/tex.The manufacturing process is distinguished by a wet stretch of the spun filaments by at least 1:4, drying under tension and a subsequent hot stretch of at least 1:2, the overall stretch being at least 1:8, preferably 1:10 to 1:20.The monofils and bristles according to the invention are suitable in particular for producing filament-reinforced composite materials.

Abstract: Free radical polymerization processes employing cobalt(II) chelates of vicinal iminohydroxyimino compounds, dihydroxyimino compounds, diazadihydroxyiminodialkyldecadienes and diazadihydroxyiminodialkylundecadienes as catalytic chain transfer agents for controlling the molecular weight of the homopolymers and copolymers produced.

Abstract: An acrylonitrile polymer film comprising at least 85 wt. % of acrylonitrile, wherein the difference in the value of the second moment of the broad-line NMR spectrum at 20.degree. C. between the film and the starting polymer powder thereof, or the polymer powder formed by dissolving the film and then precipitating the polymer from the solution, is at least 0.3 Gauss.sup.2 and the infrared dichroic ratio of the nitrile groups satisfies the requirements that 0.4<Ax/Az<0.8, 0.4<Ay/Az<0.8, and 0.8<Ax/Ay<1.25, where Ax and Ay are the absorption intensities of polarized infrared rays oscillating in respective directions parallel to the surface of the film and perpendicular to each other, and Az is the absorption intensity of polarized infrared rays oscillating in the direction perpendicular to the film surface.

Abstract: The invention relates to homopolymers and copolymers of acrylonitrile with very low Fikentscher K values of 34-15 and a total content of sulfonate and sulfate end groups, which do not originate from correspondingly substituted comonomers, of 250 to 1,000 milliequivalents per kilogram of polymer, 180 to 900 milliequivalents per kilogram being in the form of sulfonate end groups, and to suitable semi-continuous or continuous precipitation polymerization processes for their preparation by means of a redox system in an aqueous medium.The resulting polymers can be extruded to shaped articles. In particular, after hydrolysis, they can be used as emulsifiers and deep bore auxiliaries.

Abstract: An insoluble infusible electroconductive polymer is provided, which is derived from an organic compound having 3 to 6 carbon atoms and having a cyano group and an ethylenically or acetylenically unsaturated bond by mutually reacting this compound at an elevated temperature.

Abstract: The invention provides a polyacrylonitrile fiber having a tensile strength above 13 g/d and a modulus of elasticity above 2.4.times.10.sup.11 dyne/cm.sup.2, which is useful for tire cords, fiber-reinforced composite materials, precursors for producing carbon fiber, etc. The fiber is produced by integrally combining technical means which comprise using a polymer composed mainly of acrylonitrile whose weight average molecular weight is more than 400,000 and Mw/Mn ratio is less than 7.0; preparing a spinning solution from the polymer; spinning the solution into filaments; subjecting the resulting filaments to multistage stretching; and drying the filaments, all these steps being conducted under particular conditions.

Abstract: Novel acrylonitrile butadiene and carboxylated acrylonitrile butadiene elastomeric admixtures compounded with various amounts of mineral fillers such as silicates, silicas, etc., carbon blacks, and plasticizers such as esters, epoxidized polyesters, etc., are useful as continuous temperature-sensitive solids when applied to metallic conductors as coatings whereby one leg acts as a conductor and the other is used as the sensing leg. These electrical properties of these admixtures such as volume resistivity, impedance, and reactance are uniquely sensitive to temperature changes from room temperature to at least 90.degree. C. and thus offer new and important circuit design opportunities for monitoring and detecting temperature changes. These admixtures which are essentially thermosetting may be combined with other resins such as polyvinyl chloride and used thermoplastically. In these cases, the elastomer becomes the plasticizer.

Abstract: An improved process for preparing a sticky water-soluble polymer, e.g. acrylamide polymers and acrylic acid polymers, which comprises polymerizing an aqueous solution of a monomer in a polymerization vessel of which the surface contacting the aqueous monomer solution is covered with a tetrafluoroethylene-ethylene copolymer film, whereby the stickiness of the produced polymer to the vessel is remarkably decreased, namely the peelability of the polymer from the vessel is remarkably improved, and moreover the polymerization conversion is remarkably improved. Also, the use of a metal deposited tetrafluoroethylene-ethylene copolymer film as a covering material improves the efficiency of a photopolymerization and enables to use a polymerization vessel made of an inexpensive material.

Abstract: Disclosed is a method of making a conductive polymer from a non-aromatic ethylenically unsaturated gaseous monomer comprising bombarding an inert substrate with the monomer at a velocity greater than Mach 1. This can be accomplished in a vacuum using a molecular beam. Ethylene or other suitable monomer can be mixed with an inert carrier gas such as nitrogen, helium, or argon for use in the process.

Abstract: In the suspension polymerization of acrylonitrile in an aqueous medium, the polymerization is conducted in the presence of a water-soluble polymer and an oil soluble radical initiator while maintaining the acrylonitrile concentration higher than 9 weight percent in the polymerization system, whereby the polymerization of acrylonitrile in the water phase is suppressed and a high molecular weight polymer (weight average molecular weight not less than 400,000) having uniform particle diameters is produced.

Abstract: An acrylonitrile polymer comprising acrylonitrile, at least one of vinyl chloride and vinylidene chloride, a sulfo group-containing vinyl monomer having a higher reactivity ratio than acrylonitrile and a methallyl sulfonic acid monomer, which is prepared by conducting a polymerization in a manner such that at least half amount of the methallyl sulfonic acid monomer to be used is added to the polymerization system in a substantial period of adding the sulfo group-containing vinyl monomer having a higher reactivity ratio than acrylonitrile to the system. The acrylonitrile polymer is suitable for the preparation of a modacrylic synthetic fiber, and the modacrylic fiber prepared therefrom has excellent flame resistance, devitrification preventing property and dyeing affinity.

Abstract: A method for stopping and restarting the free-radical polymerization of vinyl monomers (e.g. acrylic monomers) without forming low molecular weight polymer is provided. These polymerizations utilize a Redox catalyst system comprising multivalent metal ions (e.g. iron ions) as promoter. The polymerizations are stopped by chelation of the iron present. Additional monomer is added to the polymerization to avoid formation of low molecular weight polymer. Upon restart metal ions are added to the polymerization mixture.

Abstract: High-strength filaments of dry-spun polyacrylonitrile are obtained by a process in which tension-reduced spun filaments are continuously stretched hydrothermally in one or more stages: where it involves several stages, stretching is carried out at a temperature of the stretching medium gradually increasing from stage to stage up to .theta.=.theta..sub.n and, in the final (n-th) stage, to a degree of at least 50% of the maximum degree of stretching; where it is carried out in a single stage, stretching is carried out at the optimal stretching temperature .theta..sub.n, after which the material is further treated in the conventional way, optionally with fixing of the stretched material to a pre-determined extent.

Abstract: Acrylonitrile is a monomer that is widely used in the production of a vast variety of polymers. Undesirable quantities of residual unpolymerized acrylonitrile are often present in polymers. The residual or free acrylonitrile in polymers can be reacted with certain thiols in order to reduce their content in the polymer. In the reaction between these thiols and acrylonitrile products are formed which exhibit antioxidant ability.

Abstract: Acrylonitrile polymers and copolymers with good affinity for basic dyes without sulfonic acid groups containing comonomers are obtained by polymerizing at a temperature of from 0.degree. to 60.degree. C. in an aliphatic hydrocarbon having a boiling point of from -10.degree. to 80.degree. C. or in a mixture of aliphatic hydrocarbons having boiling points in the range from -10.degree. to 80.degree. C. using an initiator system comprising from 0.1 to 8.0 mole percent of sulfur dioxide, from 0.1 to 2.0 mole percent of a hydroperoxide which is soluble in the reaction medium and from 0.01 to 1.0 mole percent of an acid which is soluble in the reaction system in that polymerization is carried out continuously and in that an average residence time of from 10 minutes to 2 hours is maintained.

Abstract: The invention relates to a homopolymer or copolymer of acrylonitrile which comprises from 0 to 30% by weight, incorporated by polymerization, of comonomer units which are free from ionic groups, said polymers having a K-value of from 50 to 100, a dye absorption capacity for cationic dyes of at least 0.5% by weight, a conductivity, measured in dimethylformamide solution, of at least 10.mu. Siemens, and from 0.2 to 1.5% by weight of sulphur fixed to said polymer as well as to a process for the production thereof.

Abstract: Polyol compositions containing effectively dispersed particulate material featuring critical dispersion characteristics are used to stabilize foam reaction in high resilience polyurethane foam.

Abstract: The invention relates to an anionic polymerization process using an initiator based on an alkali metal amide in combination with an alkali metal salt, as well as to the polymers obtained by this process.The polymerization process according to the invention is characterized in that an initiator is used which results from the combination of an alkali metal amide selected from the group comprising sodium amide, potassium amide or lithium amide and an alkali metal salt of which the cation is selected from the group comprising potassium, lithium or sodium, the anion being selected from the group comprising the thiocyanate, nitrite, cyanide and cyanate anions.These initiators make it possible to carry out the anionic polymerization or vinyl, heterocyclic and diene monomers in order to obtain special polymers or widely used polymers, with great adaptability and under advantageous economic conditions.

Abstract: Novel improved polymer/polyisocyanate composition made by polymerizing acrylonitrile alone or with one or more ethylenically unsaturated monomers in situ in a polyisocyanate. The polyisocyanate comprises a diarylalkylene diisocyanate; a polymeric diarylalkylene polyisocyanate; a quasi-prepolymer of a diarylalkylene diisocyanate or a polymeric diarylalkylene diisocyanate with an active hydrogen organic compound having at least two active hydrogen atoms per molecule; a mixture of a diarylalkylene diisocyanate, its carbodiimide and its trifunctional trimeric cycloadduct; or a mixture of two or more such polyisocyanates, to form a highly stable dispersion of small polymer particles in said polyisocyante. The novel compositions are highly useful in the production of polyurethane products.

Abstract: Method of preparing films of acrylonitrile polymer exhibiting very high tensile strength, stiffness, optical clarity, and outstanding gas barrier properties. Method entails extruding a hot, concentrated solution of said polymer in a solvent therefor that is water-soluble, e.g., dimethyl sulfoxide, onto a film-supporting surface, e.g., a flat surface, or a drum, which, preferably, has a low energy surface such as provided by wetting the surface with aqueous dimethyl sulfoxide, or coated with polytetrafluoroethylene, or other suitable means to thereby form a film. The resulting film is then contacted with an aqueous medium, e.g., water to remove the solvent (e.g., dimethyl sulfoxide) and partially replace it with water, this treatment being effected under conditions that will prevent the film from curling or puckering. The resulting film is composed essentially of acrylonitrile polymer and water, and is ignition resistant.

Abstract: The invention relates to a process for the production of polyacrylonitrile or acrylonitrile copolymers, the polymerization being carried out at a temperature of from -40.degree. to +60.degree. C. optionally under pressure in an aliphatic chlorofluorine or fluorine substituted hydrocarbon containing up to 8 carbon atoms and having a boiling point of from -60.degree. to +50.degree. C. or in mixtures thereof having boiling ranges of from -60.degree. to +50.degree. C. and using a starter system comprising a hydroperoxide sulphur dioxide and an acid. The system may also contain aliphatic hydrocarbons in such quantities that a non-inflammable mixture is formed.

Abstract: Discrete, crosslinked vinylidene chloride polymer microgels, having a latex particle size of less than 1 micron and a gel content of about 1 to 99 percent, such microgels being obtained by emulsion polymerizing (a) about 50 to about 95 parts by weight of vinylidene chloride, (b) about 5 to about 50 parts by weight of a copolymerizable ethylenically unsaturated comonomer, and (c) about 0.1 to about 10 parts by weight of a copolymerizable crosslinking polyfunctional comonomer. Such microgels have been found to have wide applicability as additives for synthetic foams and fibers, and for the preparation of improved coatings, films, and redispersible latexes.

Abstract: The invention is a process for anionically polymerizing vinyl monomers comprising contacting a vinyl monomer with an electrolytically reduced graphite having formed therein a Graphite R.sub.4 N.sup.+ intercalation compound wherein Graphite is a graphite anion radical and each R is alkyl, preferably alkyl having not more than 8 carbon atoms, to form vinyl polymer. The reduced graphite for polymerizing the vinyl monomers is prepared by electrochemical reduction of a graphite cathode in a polar aprotic solvent containing a quaternary ammonium salt electrolyte to form a graphite anion associated with a quaternary ammonium cation intercalated in the graphite. When the electrolysis is completed the graphite cathode is removed from the electrolysis cell, rinsed and contacted with vinyl monomer either dissolved in a solvent or neat to cause the polymer formation.

Abstract: A highly dispersed emulsion of an organosulfur compound is obtained by use of a coemulsification system of a surfactant, and an electrolyte, and a cosurfactant and optionally a hydrocarbon; such as a petroleum sulfonate with potassium chloride and hexyl alcohol. Conversion of organosulfur compounds into highly dispersed emulsions increases the reactivity of the organosulfur compound as a molecular weight modifier in an aqueous emulsion polymerization system and permits the efficient use of high molecular weight organosulfur compounds.

Abstract: In a process for producing an acrylonitrile polymer melt in a substantially melted state by polymerizing a monomer mixture containing acrylonitrile in the presence of water at elevated temperature under increased pressure, the polymerization is carried out continuously using a persulfate as the polymerization initiator and under a particular forced stirring as defined in the specification. This process effectively suppresses runaway polymerization reaction, facilitates the melting of the resulting polymer, and in addition produces in an industrially advantageous manner a melt of an acrylonitrile polymer having a moderate molecular weight.

Abstract: Compositions useful as multi-purpose lubricant and functional fluid additives and as thickeners and antisag additives for resins, paints and the like are prepared by free radical polymerization of at least one ethylenically unsaturated monomer in the presence of an oil-soluble dispersant. The carboxylic dispersants are preferred, especially esters of hydrocarbon-substituted succinic acids wherein the substituent contains at least about 30 carbon atoms and the reaction products of such acids or their derivatives with amines, usually polyalkylene polyamines.

Abstract: Substantially water-insoluble, water-swellable crosslinked hydrogels are prepared by polymerizing monomeric material consisting predominantly of acrylonitrile in aqueous salt solution containing zinc chloride as the main component, in absence of added crosslinking agents. The concentration of acrylonitrile is in the range of about 20 to about 40% by weight, related to the weight of the polymerization batch as a whole 100%. The process is carried out by partially hydrolyzing the primary gel thus obtained which consists of polyacrylonitrile plasticized with the aqueous salt solution, whereafter the zinc ions are removed from the gel by treating it with a dilute aqueous solution of at least one electrolyte forming an insoluble precipitate therewith. The partial hydrolysis may be carried out either by increasing the acidity of the solution or temperature or both.

Abstract: A 30-60% solution of acrylonitrile in dimethyl sulfoxide is polymerized using a redox catalyst system of water soluble bisulfite salt and a water soluble persulfate salt.

Abstract: The process enables the simultaneous production of hydroxytelechelic polymers and oligomers by the radical route. At least one ethylenically unsaturated monomer is polymerized in the presence of hydrogen peroxide under the effect of ultra-violet radiation. The polymerization is carried out in a diluent medium comprising essentially an alcohol. The process can be operated to produce polymers having average molecular weights between one hundred and one million and to produce selectively unimodal, bi-modal or multi-modal distributions of molecular weights.

Abstract: Polymer aggregates in the form of discrete particles of controlled particle size below 150 microns maximum dimension which are themselves aggregates of primary particles of a polymer or polymers derived from at least one ethylenically unsaturated monomer together with from 0 to about 400%, by weight on the weight of the monomer, of an organic thickener compatible with the monomer, said aggregate particle containing from 0 to about 95% by weight of pigment and/or extender are made by providing an aqueous dispersion of the monomer and thickener, a hydrophilic colloid being present in the aqueous phase of the dispersion and pigment and/or extender optionally being present in either the aqueous phase or the disperse phase, introducing a polymerization initiator into the aqueous phase of the dispersion, and maintaining the dispersion under conditions of high shear and continuing polymerization to substantial completion thereof. The aggregates are useful in coating comositions, e.g. to provide a matt finish.

Abstract: A method of preparing cross-linked hydrogels in the form of shaped articles, insoluble in any solvent but swellable in water and in aqueous liquids is provided. The method comprises polymerizing acrylonitrile alone or with a minor amount up to 15% by weight of monoethylenically unsaturated monomers copolymerizable with acrylonitrile under conditions of radical polymerization in concentrated, i.e. 50 to 72% nitric acid in absence of any added chain-transfer and cross-linking agents, said monomer or monomers being used in concentrations making possible cross-linking by chain transfer onto the monomer, i.e. in concentrations ranging from 15 to 50%, preferably from 25 to 40% by weight, at temperatures ranging from 0.degree. to 50.degree. C., preferably from 5.degree. to 20.degree. C. The polymerization is carried out in a mold.