Dynamic IR linear polarized spectra of thermoplastic polyester-polyurethane and nylon-6 films are recorded under a varying sinusoidal strain. Dichroic spectra are calcd. from the dynamic 0 Deg and 90 Deg polarized spectra. The large bipolar bands in the dichroic in-phase spectra, caused by large-frequency shifts of the original monopolar absorption bands, are ascribed to hydrogen bonds. This shows that esp. the hydrogen bonds are affected by stretching of the material.