Polyurethane (PU) cationomers were synthesized from polytetramethylene adipate glycol (PTAd), isophorone diisocyanate (IPDI), and N-methyl diethanolamine (MDEA) according to a prepolymer mixing process. Basic structure-property behavior of the emulsion (obtained by adding water to the ionomer solution) and emulsion cast film was studied with regard to the molecular weight (M(n)) of PTAd, MDEA content, degree of neutralization, and extender functionality. Particle size decreased asymptotically with increasing M(n) of PTAd due to the increased chain flexibility, and with the degree of neutralization due to the increased hydrophilicity of the PU. Emulsion viscosity generally showed the opposite tendency with particle size dependence. The major transition temperature, corresponding to the glass transition (T(g)) of phase mixed PU or hard segment-rich phase of the PU monotonically increased with MDEA content, degree of neutralization, and with increasing extender functionality. However, with increasing M(n) of PTAd, T(g) first decreased (M(n) = 1000) and then increased (M(n) = 1500, 2000), due respectively to the increased hard fraction of phase mixed PU, and soft segment crystallization. Tensile strength increased and elongation at break decreased with MDEA content, degree of neutralization, and extender functionality.