The behavior of specific components of elastomeric polypropylene was directly observed in situ using a dynamic, infrared polarimetry technique. The elastomeric nature of ePP is presumed to arise from a multiblock structure of isotactic (iPP) and atactic (aPP) polypropylene blocks. Elastomeric polypropylene is a heterogeneous material in terms of tacticity that can be separated into fractions differing in tacticity. A series of samples were prepared in which one fraction was labeled with deuterium. Infrared dichroism measurements made at the C-H-2 stretching vibration were used to follow the relaxation behavior of fractions of various tacticity. The samples were subjected to a series of step shear strain experiments at a variety of temperatures from the melt and into the crystalline region. By simultaneously measuring birefringence (which measures the bulk sample＇s local orientation) and IR dichroism (which measures the orientation dynamics of the deuterated fraction), it is possible to isolate the behavior of specific populations of chains. It was revealed that chains with the highest level of tacticity crystallize first, as is expected, and strongly influence the subsequent crystallization of the remaining chains. In addition, evidence of cocrystallization between the solvent fractions was observed.