Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1996-06-24
1999-01-05
Cooney, Jr., John M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 95, 521133, 521149, C08J 902
Patent
active
058563709
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to cross-linked synthetic polymers based on acrylic acid and its derivatives, which have a high absorption capacity and an improved absorption rate for water, aqueous solutions and body fluids. The present invention further relates to a process for their preparation by means of radical polymerization under conditions that result in polymers having a porous structure and a particle density which depends on the swelling degree so that the polymer particles are floatable in water or aqueous liquids. The present invention further relates to the use of these polymers for the absorption and/or retention of water and for the release of water or aqueous solutions and/or an active substance solution to a surrounding medium.
Various patents describe different synthetic polymers having an absorbing capacity for water and body fluids, e.g., cross-linked polymers and copolymers based on acrylic or methacrylic acid (U.S. Pat. No. 4,018,951; U.S. Pat. No. 4,066,583; U.S. Pat. No. 4,062,817; U.S. Pat. No. 4,066,583; DE-OS 26 13 135; DE-OS 27 12 043; DE-OS 28 13 634) or acrylamidopropane sulfonic acid copolymers (DE-PS 31 24 008). These absorbents are virtually insoluble in water and absorb in equilibrium with aqueous liquids several times their own weight of water, urine, or other aqueous solutions. Some patents also describe other properties of the synthetic absorbents in addition to the high liquid absorption capacity, e.g., low residual monomer content, low portion of water-soluble moieties, and high gel strength of the swollen polymer particles.
U.S. Pat. No. 4,529,739 and U.S. Pat. No. 4,649,164 describe polymers which have a porous structure and are based on methacrylic acid. They are obtained from ethyl acrylate/methacrylic acid copolymer latices under addition of compounds capable of separating carbon dioxide, e.g., sodium hydrogencarbonate. Austrian patent AT 391 321 B describes cross-linked, porous acrylic polymers which are produced by adding a nitrogen-containing blowing agent to the monomer solution. According to this method an N-containing blowing agent decomposing to ammonia and carbon dioxide at 80.degree. to 250.degree. C. is added to acrylic acid, either before or after the polymerization. The acrylic acid is neutralized to the extent of 60-100% with NaOH, KOH or NH.sub.3, and the added quantity of N-containing blowing agent corresponds to an increase in the neutralization degree to 102 to 140%. Ammonium salts of inorganic or organic acids and urea are mentioned as blowing agents, ammonium carbonate being preferred. U.S. Pat. No. 5,118,719 also describes ammonium and alkali carbonates used as blowing agents which are added to the monomer solution prior to polymerization. Owing to the carbonate decomposition during polymerization, carbon dioxide is formed and causes the formation of a "microcellular structure" in the hydrogel. This may explain the improved absorption rate for liquids of the final product.
The use of alkali or ammonium carbonates prior to or during the polymerization of organic acids according to U.S. Pat. No. 4,529,739, U.S. Pat. No. 4,649,164, U.S. Pat. No. 5,118,719 results in the formation of carbon dioxide during the neutralization of the monomer solution. Since CO.sub.2 has a limited solubility in the monomer solution and in the polymer gel mass, only relatively small amounts of CO.sub.2 can be incorporated into the polymer during polymerization or drying. Also, the alternative according to AT 391 321 B, i.e., to add the blowing agent to the polymer gel prior to drying, does not result in the desired effect because of the superficial action of the aftertreatment. This method has the disadvantage that the added water amount must be removed during drying. Also, an excessive use of ammonia does not result in highly porous structures in swollen gel condition, since ammonia is readily soluble in water or aqueous liquids. Thus it is dissolved during swelling and the porosity of the hydrogel particles substantially disappears. Moreover, the addition of ammonia
REFERENCES:
patent: 4918110 (1990-04-01), Kuo et al.
patent: 5026738 (1991-06-01), Meinhard
patent: 5219969 (1993-06-01), Uhl et al.
Cooney Jr. John M.
Stockhausen GmbH & Co. KG
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