Self-, co-organisation behaviour and encapsulation efficiency of waterborne polyurethane pre-polymers

Abstract

Polyurethane-prepolymers are the precursor for waterborne polyurethane coating applications. The physical–chemical behavior of the pre-polymers are worth thorough investigation, since they will largely influence the final properties of coating products [1–3]. In this paper, we experimentally studied the self-, co-organization characteristics and encapsulation efficiency of a polyurethane pre-polymer in aqueous electrolyte environment, by means of light scattering and small angle X-ray scattering. Due to the amphiphilic nature, pre-polymers are expected to form micelles in water. Systematic studies were conducted on dispersions at different pre-polymer concentrations and salt concentrations. Our experiments show that the micelles have a radius of about 10 nm and are stable over a broad range of salt concentrations; only at high salt, 100 mM NaCl, we observe the onset of colloidal instability. Moreover, we find that the amphiphilic pre-polymers are able to encapsulate hydrophobic counterparts, forming particles with radii of about 130 nm. The threshold ratio of hydrophilic over hydrophobic pre-polymers to form stable dispersion is found to be 5:1.