Phase transformation on heating of undercooled melt of poly(ethylene oxide)-urea molecular complex

X-ray and calorimetric investigations of the structure and transformations on heating of quenched (undercooled) samples of poly(ethylene oxide)-urea molecular complexes are discussed. It was established that at room temperature the undercooled melt of the molecular complex contains free urea in a tetragonal crystal modification and a high-temperature poly(ethylene oxide)-urea molecular complex whose crystal modification does not coincide with the known hexagonal crystal structure of the molecular complex obtained from solution or by slow cooling from the melt. It was shown that on heating this molecular complex to a temperature between 87,5 and 90°C, the hexagonal crystal modification, stable at room temperature, is obtained.