Polyurethane ionomers: Order in 4,4′‐methylenedi(phenyl isocyanate)‐ and hexamethylene diisocyanate‐based poly(ether‐urethane) cationomers

Polyurethane cationomers from poly(oxytetramethylene) of molecular weight 2000 as soft segments, 2,2′‐methyliminodiethanol as chain extender, glycolic acid as quaternization agent, and 4,4′‐methylenedi(phenyl isocyanate) (MDI) and hexamethylene diisocyanate (HDI) as diisocyanates are synthesized and characterized by using wide‐angle X‐ray diffraction, dynamic mechanical analysis, differential scanning calorimetry and tensile‐elongation testing. It is found that, in the unionized and ionized cases, the hard segments exhibit a disorder and short‐ and long‐range order, but no crystallinity. The ordered hard segments in the hard domains aggregate so tightly as to act as crosslinks, such that crystallization of soft segments occurs during elongation. Such disorder and order are also found to exist in the solutions of ethyl methyl ketone as reflected in variations of conductivity and viscosity during addition of water at 20°C. Ionization by insertion of the acid can disrupt the order in MDI and HDI systems, but can increase the cohesion between the neighbouring hard segments, the latter being predominant over the former. Dispersion is apt to disrupt the long‐range order in HDI systems but has only an insignificant effect on the order in MDI systems.