Ionomeric blends. V. FTIR studies of ionic interactions in polyurethane‐styrene blends

FTIR spectra of blends of lightly sulfonated polystyrene (PS‐SSA) with polyurethanes (PU) containing a tertiary nitrogen in the chain extender were recorded. These blends exhibit a two‐phase behavior, but the individual components are not phase separated. Earlier dynamic mechanical studies suggested the occurrence of proton transfer from the sulfonic acid to the tertiary nitrogen, which enhanced the miscibility via ionic interactions and resulted in the formation of a miscible blend between the PS‐SSA and the hard segment of the PU, the soft segment being excluded. FTIR studies of these blends now confirm the proton transfer mechanism. A new absorption band at 3428 cm⁻¹ corresponds to a stretching vibration of an N⁺−H bond. The 1012 cm⁻¹ band of the SO₃H group, which strongly depends on the degree of protonation, shifts to lower frequency. The symmetric stretching vibration of the SO 3− group, which occurred at 1043 cm⁻¹, shifts to lower frequency as well, suggesting a lower polarization of the SO dipole due to the removal of H⁺.