Phase separation in segmented polyurethanes

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Abstract
Phase separation in a segmented polyurethane has been studied by differential scanning calorimetry. The glass transition temperature of the soft phase decreases logarithmically with time to a limiting value at each annealing temperature. The magnitude of the decrease is larger at low annealing temperatures, but the normalized rate of logarithmic decrease is smaller. At high annealing temperatures, long sequences of hard segments are excluded from the soft phase in which short segments are still soluble. At low temperatures, even short hard segments separate from the soft phase. The exclusion of the hard segments from the soft phase is a relatively fast process, but the development of order in hard domains takes longer time to reach steady state.