Physical Properties of Nonionomeric and Ionomeric Segmented Polyurethanes: Effect of Sulfonate, Carboxylate, and Quaternary Ammonium Ions in the Hard Segment

Polyurethane ionomers are of practical interest because of structural properties which result from ion pair interactions. In some ionomers, the ions are located in the backbone of the polymer, while in others, they are present in pendant groups. These variations, combined with variations in ion type can provide materials with a broad range of structures. In this work, derivatization chemistry was used to vary the ion type in sulfonated polyurethanes by attaching different amino acids (lysine, aspartic acid, glycine, and arginine methyl ester) as pendant moieties to the sulfonate groups, via sulfonamide linkages. While the modified materials had similar amino acid concentrations and molecular weights, they each displayed unique mechanical properties. Differential scanning calorimetry was used to investigate the structure of these polyurethanes and showed that the supramolecular structural elements (microphase domains) are disassembled upon heating. It was also shown that ammonium type cations undergo a first-order endothermic thermal transition in these materials at elevated temperatures. The superposition of ionomer character on the microphase-separated structure of segmented polyurethanes appears to add significantly to their range of mechanical behavior and could provide materials with new end use applications.