Nanostructured and hollow polyurethane dispersions

Abstract

Due to their superior properties, ease of use and ‘green’ nature, water-borne polyurethane dispersions (PUDs) are often materials of choice for a wide spectrum of applications. Common processes for making these dispersions do not offer easy ways of controlling particle morphology/architecture. This puts PUDs in a position inferior to structured acrylic emulsions. The latter are most readily produced by the sequential or staged addition of monomers with is widely used in the engineering of structured acrytic and vinyl emulsion polymers. Because PU oligomers do not diffuse through the aqueous phase, this route is closed for PUDs. How car this fundamental obstacle be overcome? In this paper, a new method is described that enables the preparation of nanostructured PU particles with a wide variety of morphologies. The method is comprised of the preparation of two prepolymers with different hydrophilicities, which are mixed together before the dispersion step Surprisingly, the mixture ‘remembers’ that it is made of two different prepolymers, and as soon as the prepolymer is dispersed in water, diffusion within the particles sets in. The origin of this unexpected memory is examined in detail. The interplay of diffusion, phase separation and chain extension determines the morphological outcome. Various previously inaccessible PU particle morphologies, including core-shell, ‘ice-cream cone’, lobed and hellow particles, have been prepared. This novel patent-pending technology opens up new horizons for PUD chemistry.