AQUEOUS DISPERSIONS CROSS-LINKED IN AN ALKALINE MEDIUM,AND SHAPED ARTICLES PRODUCED THEREFROM

1,146,890. Aqueous dispersions of polyurethanes. FARBENFABRIKEN BAYER A.G. 5 June, 1967 [8 June, 1966], No. 25809/67. Heading C3R. Aqueous dispersions of polyurethanes are obtained from polyurethanes prepared from a compound containing reactive hydrogen atoms at least one of which is contained by a hydroxyl group and having a M.W. of 300 to 20,000, a polyisocyanate, and, if desired a chain extending agent and a compound having at least one group reactive with isocyanate groups and which contains at least one sulphuric acid semiester group of formula O-SO 3 M, where M is an alkali metal atom, ammonium or amino group, in a quantity such that the proportion by weight of the group O-SO 3 (-) amounts to 0À05 to 8% by weight of the polyurethane. The dispersion may be formed (a) by first forming an isocyanate terminated prepolymer which is reacted in an organic solvent with the compound containing the O-SO 3 M group followed by the addition of water and removal of the organic solvent or (b) by adding the prepolymer solution to an aqueous solution of the compound containing the O-SO 3 M group or vice versa. Cross-linked polyurethanes are obtained by first making the aqueous dispersions alkaline, partly drying them in a shaping process and then subjecting them to a heat treatment. During the heating under alkaline conditions the sulphate groups are split off and the polyurethanes cross-linked. Conventional, high molecular weight active hydrogen-containing polymers, polyisocyanates and chain extending agents may be used. The compound containing the O-SO 3 M grouping is suitably derived from such compounds as aminoethanolsulphuric acid, imino-bis-ethanolsulphuric acid, ethylene-bis-aminoethanol sulphuric acid, aminopropanol sulphuric acid, hexamethylene diamine-N,N1-diethanolsulphuric acid and hexamethylene-diaminemonoethanol sulphuric acid.