Azo dyestuff- and urethane-containing polyadducts comprising (a) at least one organic polyisocyanate, (b) at least one diol of a heterocyclic azo dyestuff, and if desired (c) one or more compounds having at least two groups reactive to NCO, which have an average molecular weight M.sub.n of up to 500 g/mol, and/or (d) one or more polyhydroxy compounds having average molecular weights M.sub.n of from over 500 up to 5000 g/mol. These polyadducts are suitable for applications in nonlinear optics.

Water-emulsifiable polyisocyanates, containing a) aliphatic, cycloaliphatic or aromatic polyisocyanates and b) reaction products of the abovementioned polyisocyanates with compounds which contain at least one group ##STR1## in short called a sulfo group, and at least one isocyanate-reactive group.