Evidence for Structural Transformations in Polymer Melts

Crystallizing and non-crystallizing polymers have been investigated by Brillouin spectroscopy in the liquid state. The temperature gradient of the sound velocity of crystallizing polymers shows a discontinuity at ∼60–110K above the melting transition. The non-crystallizing polymers investigated show no uniform behaviour. We interpret the phase between the melt temperature and the temperature of the additional transformation as a phase of locally nematic structure. This interpretation is also supported by a study of density, refractive index, viscosity and hypersonic attenuation.