Segmental orientation and chain relaxation of polymers by Fourier transform infrared dichroism

Fourier transform infrared dichroism has been used to investigate molecular orientation in polymeric materials. It is first applied to characterize ne twork behavior in some elastomeric systems such as model networks of poly(d imethylsiloxane). The strain dependence of segmental orientation is analyze d through networks of known degree of cross-linking and experimental result s are compared with calculation predictions based on the rotational isomeri c state formalism. Infrared dichroism spectroscopy has also been used to an alyze orientational relaxation in binary blends of long and short polystyre ne chains. The effect of short deuterated chains (M-W = 3000 to 72000) on t he orientational relaxation of long entangled chains (Mw = 2 000 000) is ex amined in the bidisperse melts uniaxially deformed above the glass transiti on 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 in agreement with the classical relaxation t heories.