A novel method of preparing an aqueous dispersion of non-uniform
polyurethane particles which comprises (a) preparing at least two
isocyanate-terminated polyurethane prepolymers having different
hydrophilicities; (b) preparing a uniform mixture of said prepolymers;
and (c) dispersing the mixed prepolymers in an aqueous medium. The
resulting dispersion of the prepolymers may optionally be chain extended.
This method enables the preparation of core-shell particles as well as
particles of other morphologies, including "raspberry", interpenetrating
network, "salt-and-pepper", "ice-cream cone" and particles of gradient
composition. Similarly, an aqueous dispersion of two different
polyurethane polymers may be obtained by first preparing at least two
different isocyanate-terminated polyurethane prepolymers, preparing a
uniform mixture of such prepolymers and thereafter dispersing the mixture
in an aqueous medium.