Thermoplastic polyurethanes with polycarbonate soft phase: Effect of thermal treatment on phase morphology

The thermal sensitivity of thermoplastic polyurethanes with polycarbonate soft phase (PCU) is considered. Thermal treatments were coupled with differential scanning calorimetry and infrared spectroscopy to investigate the effect of temperature on the phase morphology. PCU is characterized by a biphasic morphology: ordered hard polyurethane micro-domains are dispersed in a soft phase matrix, containing both hard and soft segments. Heating may completely destroy the short and long range order or simply change it. The infrared behaviour of the CO and NH stretching regions gives information on the organization of the segments. Thermal treatments above the processing temperature lead to an unstable monophasic morphology, that at room temperature is subjected to segregation of the hard segments, in order to recreate the biphasic morphology. Annealing treatments below the processing temperature cause reorganization in the hard micro-domains, inducing changes in their amount and dimensions. The result of the annealing depends on the temperature and on the exposure time. The thermal sensitivity also involves the chemical properties, given the thermal lability of the urethane bonds in the range of the processing temperature.