AbstractThe phase‐separation process in segmented copolymers is treated by first‐order kinetics which couples with the Fox equation to derive an expression for describing the change of soft segmentTgwith the annealing time. Kinetic data of five commercial polyurethanes have been analyzed. The studies conclude that the phase‐segregation mechanisms involve two elementary steps which can be characterized by two discrete relaxation times. It has been shown quantitatively that a polyether‐based polyurethane (ET) recovers its original domain structure faster than a polyester soft‐segment material. The average activation energy of the demixing process of an ET polyurethane is found to be about 23 kJ.mol−1and is not influenced by hydro
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