Synthesis and Characterization of Segmented Polyurethanes Containing Trisaminocyclopropenium Carbocations.

Diol-functionalized trisaminocyclopropenium (TACP) carbocations were used as chain extenders in a two-step synthesis of a segmented polyurethane. Differential scanning calorimetry demonstrated significant differences in the crystallization behavior of the poly(tetramethylene oxide) soft segment when minor changes were made to the TACP structure and when compared to a control that was chain extended with butane diol. Fourier transform infrared spectroscopy was used to characterize the different level of hydrogen bonding in the polymers and showed that the bulky, charged TACP chain extender limited hydrogen bonding interactions when compared to the control. Dynamic mechanical analysis was used to probe the thermomechanical behavior of polymers that showed that the TACP-containing polymers were much more resistant to flow at high temperatures when compared to the control. Small-angle X-ray scattering showed a phase separated morphology for all the polymers tested. Tensile testing of the TACP polyurethanes demonstrated an elastic response over a wide range of strain, followed by a significant strain hardening. These results suggest a morphology of ionic aggregates rather than hard segment physical cross-links.