Process for the production of polyurethanes

摘要

Elastic polyurethanes are prepared by forming a prepolymer by reacting a molar excess an organic diisocyanate with a dihydroxyl compound of formula wherein R1 is a divalent aliphatic, cycloaliphatic or araliphatic radical, R2 is a divalent aliphatic radical, R3 is a monovalent saturated or unsaturated aliphatic, cycloaliphatic or araliphatic radical and x is a number larger than 3, and the resulting prepolymer is reacted in solution in a polar organic solvent with a chain extender. The chain extender may be a glycol, diamine, aminoalcohol or hydrazide and the solvent may be dimethyl formamide, dimethyl acetamide, N-methyl pyrrolidone, dimethyl sulphoxide, methyl ethyl ketone, dioxan, tetrahydrofuran or chlorobenzene. The dihydroxy compound can be produced by reacting 1 mol. of the bischloroformic acid ester of a polyether of formula H-(OR1)x-OH with 2 mols. of an amino alcohol HO-R2-NHR3 in aqueous organic medium. In Example (1) the bischloroformic acid ester of polytetrahydrofuran was reacted with N-methyl ethanolamine and the product reacted with tolylene diisocyanate followed by diphenylmethane diisocyanate in chlorobenzene, and the prepolymer obtained thereby reacted with carbodihydrazide in dimethylformamide. The solution was pigmented with TiO2 and hexane 1,6-diisocyanate added.