Nanostructured polymers: A molecular interpretation of nanoscale reinforcement in polyurethane/polyimide blends

A series of segmented poly(ether-urethane-urea)/polyimide blends were characterized using Small angle x-ray scattering (SAXS), tensile testing, dynamic mechanical analysis (DMA), and Fourier-Transform Infrared (FTIR) Spectroscopy. The SAXS revealed a dependence of the domain size, interdomain distance, and degree of phase mixing on polyimide concentration. The reduction in domain size was accompanied by an increase in interdomain distance and phase mixing. The FTIR studies showed that PI chains dispersed in the PU were stabilized by the formation of hydrogen bonding. In addition, free urea carbonyl absorption bands appeared as a function of PI concentration implying an interference with the formation of hard domains in the PU. The PU/PI blends showed large improvements in tensile properties at low concentrations (1-5 wt. % PI). The enhancement in mechanical properties is attributed to synergism between the molecularly dispersed nanosize rigid segments and the formation of hydrogen bonding.