Potassium ion‐based polyurethane anionomers: effects of emulsification on structure and physical properties

Abstract

AbstractA polyurethane was prepared using poly(oxytetramethylene) as soft segments, 4,4′‐methylenedi(phenyl isocyanate) as diisocyanate and 2,2‐bis(hydroxymethyl)propionic acid as chain extender, and then ionized with potassium hydroxide to yield the potassium ion‐based PU anionomer. The resulting PU anionomer solution in ethyl methyl ketone was emulsified by continuous addition of water. In the unionized film, soft segment crystallites are not present. Ionization creates soft segment crystallites and produces increased cohesion in the hard domains, which leads to an increase in both tensile strength and elongation at break. Emulsification of the PU ionomer solution leads to slightly increased phase separation. During the emulsification, conductivity and viscosity variations show that water is first adsorbed on the surface of the hard‐segment microionic lattices and then enters into the disordered hard domains. The morphology of the unionized film shows that the hard domains are dispersed in the soft domains and tha the size of hard domains increases greatly after the ionization. After dispersion, the hard segments originally distributed in the dispersed phase undergo phase inversion and adopt a morphology of interwoven soft and hard domains. Compared with other PU anionomers, the present system is branched rather than linear, as reflected in the good mechanical properties of the present system.