Ceskoslovenska Akademie Ved

Renata Urbanova

Artur Stoy

Vladimir Stoy

Josef Kucera

Jaroslav Prokop

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. The lyogel thus obtained is then kept within the same temperature range until the desired swelling capacity in water is reached, and nitric acid is removed by washing the casting in water or in aqueous liquids.

Method of preparing cross-linked hydrogels

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 the 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. The lyogel thus obtained is then kept within the same temperature range until the desired swelling capacity in water is reached, and the nitric acid is removed by washing the casting in water or in aqueous liquids.

Method of preparing shaped articles from cross-linked hydrogels

Solutions of polymers or copolymers containing up to 100% of acrylonitrile units and from 0 to 50 mol percent of units of one or more comonomers copolymerizable with acrylonitrile into nitric acid-soluble polymers is wet spun in a coagulating bath containing a constant surplus of neutralizing agents in an amount ranging from about 0.05 to about 5% by weight which neutralizing agents are sufficient to convert the nitric acid into nitrates and to make the filaments leaving the coagulating bath free of nitric acid. The coagulating bath is maintained at a temperature at least about 5.degree. C above the temperature at which the solution of the same concentration is saturated with respect to its nitrate content. The concentration of the coagulating bath is kept constant during the wet spinning by withdrawing a part of the bath equimolar to the amount of nitric acid introduced therein by the wet spinning, adding a neutralizing agent to the bath at a rate at which the nitric acid is introduced into the bath and replacing the water lost from the bath during the withdrawing of the portion thereof. The filament fibers are concommitantly formed by washing, stretching, heat stabilizing and drying the material as it leaves the bath, together with the formation of nitrates by treating the withdrawn portion of the bath in conventional manner to recover in solid form the nitrates found in the withdrawn bath.

Method of simultaneously manufacturing acrylic fibers and nitrates

There is disclosed a method of preparing hydrophilic copolymers of acrylonitrile by initially polymerizing acrylonitrile with about 0.01 to about 30% by weight of a monomer selected from the group consisting of acrylamide; methacrylamide; monomers of the formula CH.sub.2 =CRCONHR.sup.1 wherein R is hydrogen or methyl and R.sup.1 is hydrogen, methyl or ethyl; N,N-dialkylacrylamides and methacrylamides and N-alkylol amides, thereafter subjecting said copolymer to hydrolysis by an aqueous acidic solvent for the monomers or swelling agent for the polymer comprising at least one compound selected from the group consisting of nitric acid, sulfuric acid, phosphoric acid, formic acid, zinc chloride and zinc chloride/HCl mixtures and subsequent isolating the product thus formed by removal of the acidic hydrolytic agent therefrom. The products thereof possess such properties as high tensile strength and high swelling capacity and they are accordingly suitable for the production of fibers, membranes, tubing and the like.

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Prague, Czechia

Renata Urbanova