A digital absorbance subtraction procedure for the isolation of absorption bands assocd. with certain cryst. modifications or rotational isomers of various semicryst. polymers, e.g. nylon 6 [25038-54-4], poly(alkylene terephthalate), were reported. A recently developed technique to characterize the deformation mechanism in polymers by dynamic Fourier transform IR dichroism studies with polarized radiation were discussed with ref. to exptl. results from polyethylene [9002-88-4] and polypropylene [9003-07-0].