Waterborne polyurethanes containing ionic groups in soft segments

Polyurethane ionomer dispersions were prepared with ionic groups in soft segments (called ionic soft segments) as well as in hard segments (ionic hard segments). Ionic soft segments gave significantly lower solution viscosity, smaller particle size and greater dispersion viscosity, larger contact angle with water and greater water compared with ionic hard segments. These properties were interpreted in terms of delocalization of hydrophilic groups among soft segments and hard segments leading to increased soft segment-hard segment phase mixing, evidenced from IR, thermal and dynamic mechanical measurements which proved a higher glass-transition temperature, T-g, and greater phase mixing with ionic soft segments. The increase in the hard segment length as well as the cross-linking density also gave a higher T-g, modulus, and yield strength for the ionic soft segments.