Preceding parts (S. 1983) discussed results of rheooptical Fourier-transform IR investigations at ambient and elevated temps. obtained from a series of model poly(ester urethanes) (I) with varying compn. in terms of phase sepn. and segmental orientation of I; the potential of this technique applied to NH-deuterated specimens of I was demonstrated with ref. to a more detailed insight into phase sepn. and orientation mechanism of the phase-sepd. hard segments during uniaxial elongation and recovery. The I were prepd. from 4,4'-diphenylmethane diisocyanate, a dihydroxy-terminated adipic acid-butanediol-ethylene glycol polyester (mol. wt. 2000), and butanediol chain extender at various ratios, and then deuterated. The most obvious spectral changes on deuteration directly reflected those absorption bands belonging to vibrations involving the NH groups. The stress-strain diagrams of deuterated samples measured at 300 K did not deviate significantly from corresponding mech. data of original undeuterated specimens. Orientation functions of hard and soft segments derived from the dichroism of n(NH) and n(CH2) absorption bands, resp., in polarization spectra monitored during loading-unloading cycles of deuterated I at 300K were shown. The n(NH) orientation function represented the orientation of inaccessible hard segment domains.