Reaction of organic diisocyanates with water

In a process for the preparation of an organic polyisocyanate which comprises reacting an aliphatic, alicyclic or araliphatic diisocyanate monomer with water, the improvement which comprises conducting the reaction

• (a) at a reaction temperature of at from about 70.degree. C. to about 200.degree. C.;
• (b) in the presence of a solvent mixture comprising a mixture of at least one ethylene glycol derivative of the formula (I):
• R.sub.1 O(CH.sub.2 CH.sub.2 O).sub.n R.sub.2 (I)
• wherein R.sub.1 and R.sub.2, which may be the same or different, each represents an alkyl group having 1 to 4 carbon atoms, which may be straight chain or branched chain, or an acetyl group and n is an integer of 1 to 2;
• and at least one phosphoric acid derivative of the formula (II):
• ##STR3## wherein R.sub.3, R.sub.4 and R.sub.5, which may be the same or different, each represents a methyl group or an ethyl group;
• (c) with the proportion of the solvent mixutre in the reaction mixture being 10 to 80 wt%;
• and
• (d) with the proportion of the ethylene glycol derivative (I) in the solvent mixture being 30 to 90 wt% and the proportion of the phosphoric acid derivative (II) in the solvent mixture being 10 to 70 wt%, wherein the molar ratio of the diisocyanate monomer to water ranges from about 5:1 to about 40:1, said solvent mixture providing the dual effects of substantially completely eliminating the formation of by-product polyurea and inhibiting the amounts of monomer present after long term storage of the reaction product.