GB1226806A - - Google Patents

Abstract

1,226,806. Microporous sheets. FARBENFABRIKEN BAYER A.G. 6 Aug., 1968 [9 Aug., 1967], No. 37433/68. Headings C3C and C3R. Microporous sheets are prepared by coagulating a polyurethane or polyurethane urea which is dissolved in a highly polar organic solvent by using a non-solvent in the presence of 2 to 1500% by weight, based on the weight of the solid polyurethane or polyurethane urea, of an ionic compound which contains water of crystallization or a metal oxide which in aqueous solution is in equilibrium with the corresponding hydroxide, the ionic compound and the metal oxide having either (a) an enthalpy of hydration of less than 18 k. cal./mole and a solubility of less than 150 g./100 g. in dimethylformamide or dimethylacetamide, or (b) an enthalpy of hydration of more than 18 k. cal./ mole but a solubility of less than 15 g./100 g. in the above solvents, the enthalpy of hydration of the metal oxide being represented by the equilibrium constant for the metal oxide/metal hydroxide reaction and when a metal oxide is used, any additional polymers or copolymers present. must not contain any free carboxyl groups. The polyurethanes and polyurethane ureas may be prepared by conventional techniques and may be dissolved in dimethylformamide or dimethylacetamide or in a mixture of such solvents together with a less highly polar solvent such as tetrahydrofuran, dioxane, acetone or ethylene glycol monomethyl ether acetate. Numerous ionic compounds and metal oxides are listed, those specifically exemplified being aluminium sulphate octadecahydrate, ferrous sulphate heptahydrate, barium chloride dihydrate, ferric phosphate tetrahydrate, sodium dihydrogen phosphate dihydrate, potassium aluminium sulphate dodecahydrate, zinc oxide, copper sulphate pentahydrate, chromium-III- acetate hydrate, a cuprammonium sulphate solution and ferrous ammonium sulphate decahydrate. The ionic compound or metal oxide may be added in finely divided solid form, dispersed or in solution in e.g. dimethylformamide, dimethylacetamide, water, alcohols or acetonitrile. Suitable non-solvents are water, alcohols, ethers, mineral oil and oil of turpentine. A film cast from the polymer solution is washed with the non-solvent until the solvent is removed and then dried.