A series of surfactant free aliphatic PUD's, prepared with no organic solvent, were used as the first stage (seed) in the preparation of acrylic hybrid latices. The acrylic component consisted of various comonomers of methyl methacrylate, n-butyl acrylate and styrene. By using a combination of film formation, DSC, TEM, and SEM measurements, the composite latex morphologies were characterized for a wide variety of experimental conditions. Essentially all latex reactions resulted in non-equilibrium morphologies with a great deal of mixed polymers in the particles, but all reactions yielded colloidally stable latices at 20% total solids. Hydrogen bonding between the amine units in the PU and the carbonyl groups on the acrylic polymer chains was responsible for the lack of polymer phase separation in the particles. Removing the carbonyl groups in the second stage monomer and/or thermally annealing the finished latex or dried films above 130 degrees C, allowed nearly complete phase separation to occur. In addition it was found that all of the PU based latex particles contained surprisingly large amounts of water. (C) 2018 Elsevier Ltd. All rights reserved.