Structural Changes near the Glass Transition–Neutron Diffraction on a Simple Polymer

Using neutron diffraction, the structural change of a backbone polymer, polybutadiene, is studied when heated from the glass to the melt. On a microscopic scale the temperature dependence of the linear thermal expansion shows a discontinuity below the calorimetric glass transition temperature T g , whereas the correlation length for monomer or chain ordering becomes independent of temperature near T g . These effects appear in the range where we recently have observed changes in the inelastic excitation spectrum of this sample.