| abstract |
A water-diluted, ungelled, non-sedimenting polyurethane and a process for preparing such a polyurethane in an aqueous medium is disclosed. High molecular weight thermoplastic products are obtained by chain extending in aqueous medium an NCO polymer having a salt group equivalent weight of 6000 or less and substantially free of reactive hydrogen. The average functionality and equivalent ratio of the polyisocyanate and active hydrogen-containing materials used in making the NCO polymer, as well as the functionality of the chain extender, are carefully controlled so as to get high molecular weight ungelled products. Thermosetting compositions can be made by adding curing agent to the chain extended material. Curing agents can also be incorporated into the polymer molecule either in the making of the partially reacted NCO-containing prepolymer or by further reaction with the partially reacted NCO-containing prepolymer. The water-dispersed polyurethanes of the present invention are excellent film formers, capable of making coatings with a wide spectrum of desirable properties. In addition, they can be added to other water-compatible compositions to improve flexibility, hardness, drying and other coating properties. |