ANALYSIS OF ORIENTATIONAL RELAXATION IN BINARY BLENDS OF LONG AND SHORT POLYSTYRENE CHAINS BY FOURIER-TRANSFORM INFRARED DICHROISM AND SMALL-ANGLE NEUTRON-SCATTERING

Measurements of the local orientational order and average chain anisot ropy in non-uniform polystyrene are reported. Fourier-transform infrar ed dichroism spectroscopy has been used to determine the effects of sh ort deuterated chains (Mw = 500 to 188 000) on the orientational relax ation of long entangled chains (Mw = 2 000 000) in bidisperse melts un iaxially deformed above the glass transition temperature. While the lo ng-chain relaxation is found to be dependent on the short-chain concen tration, the local orientational order of the latter is molecular weig ht dependent consistent with the classical relaxation theories. The FT IR experiments are also combined with small-angle neutron scattering m easurements which probe the deuterated-chain anisotropy in the defomed melts. There is evidence, from the combination of the two techniques, that although the short chains possess a negligible local orientation al order, there exists an important anisotopy in the short chain distr ibution in space.