Variable temperature dynamic mechanical analysis (DMA) and Fourier transform infrared spectroscopy (FTIR) have been combined and applied to rheooptical (DMA-FTIR) studies of thin films of a poly(ester urethane). In this study, dynamic infrared linear dichroism (DIRLD) measurements have been carried out at 25, -5, and -30 degreesC with the step-scan FTIR modulation/demodulation technique. The changes in both the in-phase and quadrature spectra as a function of temperature reveal different responses for the various functional groups as a function of temperature. In particular, as the temperature is lowered, the dynamic responses of structurally different carbonyl groups (hydrogen-bonded, free, urethane, ester) are clearly differentiated. The changes in dynamic response are related to changes in the hydrogen-bonding interactions in this polymer as well as to distinction between different molecular-level microenvironments.