Phase mixing and separation in polyester polyurethane studied by small-angle scattering: A polydisperse hard sphere model analysis

Small-angle scattering was employed to characterize the gradual phase mixing and separation of Estane 5703p, a type of polyester polyurethane, as a function of temperature (20–110 °C) and time (minutes to 80 days). The polymer structure was modelled by polydisperse hard spheres, and microstructure evolution of the material was inferred from the development of the fitting parameters. At temperatures higher than 40 °C, the scattering data indicated the mixing of hard domains (MDI-BDO) with soft matrix (PBA). The hard domain distance showed a sharp increase at 50–60 °C. Between 60 and 90 °C, a newly-observed ordering signalled the formation of a distinct mesophase with a repeat distance of 5.15 nm. Upon heating, the morphology evolution in Estane follows: domain intermixing – mesophase formation – final melting. After cooling, the domain structure partly recovered, but did not reach the original state during storage at room temperature for 80 days.