Morphology, Dynamic Rheology, and Cohesive Properties of Epoxy-Modified Polyurethane-Acrylate Microemulsions Prepared by In Situ Surfactant-Free Polymerization

A series of organic, solvent-free, epoxy-modified polyurethane-acryalte (EPUA) adhesives were prepared through in situ surfactant-free polymerization. Stable EPUA microemulsions with average particle diameters of less than 100 nm and a unimodal distribution were obtained through control of the epoxy content. Transitions from irregular shapes with a heterogeneous size distribution to a regular spherical particle morphology with an apparent core-shell morphology were obtained for EPUA with an increasing epoxy content to 8 wt %. With epoxy addition, EPUA displayed pseudoplastic behavior instead of Newtonian behavior, and increases in the viscosity and pseudoplastic behavior were detected. In addition, the EPUA emulsion transferred from a viscous liquid to a solidlike liquid. The addition of epoxy was beneficial for phase mixing, interaction, and entanglements between polyurethane and polyacrylate, and the interactions between the EPUA colloidal particles were also enhanced. The thermal stability, mechanical properties, and water and solvent resistance were thereby improved, as was the cohesive properties. However, the corresponding properties were weakened with excessive epoxy, and this was ascribed to the greatly increased particle size, viscosity, and phase separation. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39886.