Abstract: Novel polymers of excellent heat- and flame-resistance are obtained by reacting together an aqueous solution of an aminoplast precondensate such as a urea-formaldehyde syrup, an organic polyisocyanate comprising di(isocyanatophenyl)methane or a mixture of di(isocyanatophenyl)methane with poly(isocyanatophenyl)polymethylenes, and an isocyanate-reactive organic polyol in the presence of a tertiary amine as catalyst and a poly(haloalkyl)phosphate, especially tris-(2-chloroethyl)phosphate.Under normal circumstances, foamed materials are obtained, but non-foamed materials can be obtained by carrying out the reaction in the presence of a CO.sub.2 absorbent.