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 anisotropy in non‐uniform polystyrene are reported. Fourier‐transform infrared dichroism spectroscopy has been used to determine the effects of short deuterated chains (Mw = 500 to 188 000) on the orientational relaxation of long entangled chains (Mw = 2 000 000) in bidisperse melts uniaxially deformed above the glass transition temperature. While the long‐chain relaxation is found to be dependent on the short‐chain concentration, the local orientational order of the latter is molecular weight dependent consistent with the classical relaxation theories. The FTIR experiments are also combined with small‐angle neutron scattering measurements 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 orientational order, there exists an important anisotopy in the short chain distribution in space.