PURPOSE: To prepare the title dispersion, economically, without washing with water after the neutralization process, by hydrolyzing a urethane bond-containing polyisocyanate with sulfuric acid and water, neutralizing the hydrolyzate with a basic compound such as calcium, etc., and finally emulsifying the product.

CONSTITUTION: A polyisocyanate having urethane bonds, pref. of formula (R is diol residue having a molecular weight of 500W15,000; R' is divalent hydrocarbon radical; n is 1W25) is hydrolyzed with sulfuric acid and water. The polyamine sulfate thus obtained is neutralized with a basic compound of Ca or Ba, e.g. Ca(OH)2, until pref. ≥55% of the polyamine salt is converted to the free polyamine. The neutralized product is emulsified with an emulsifier, etc. to obtain the objective aqueous solution of diamine.

USE: Waterproofing material, paint, adhesive, etc. by mixing with an epoxy resin, etc.