The behavior of specific components of elastomeric polypropylene was direct
ly observed in situ using a dynamic, infrared polarimetry technique. The el
astomeric nature of ePP is presumed to arise from a multiblock structure of
isotactic (iPP) and atactic (aPP) polypropylene blocks. Elastomeric polypr
opylene is a heterogeneous material in terms of tacticity that can be separ
ated into fractions differing in tacticity. A series of samples were prepar
ed in which one fraction was labeled with deuterium. Infrared dichroism mea
surements made at the C-H-2 stretching vibration were used to follow the re
laxation behavior of fractions of various tacticity. The samples were subje
cted to a series of step shear strain experiments at a variety of temperatu
res from the melt and into the crystalline region. By simultaneously measur
ing birefringence (which measures the bulk sample's local orientation) and
IR dichroism (which measures the orientation dynamics of the deuterated fra
ction), it is possible to isolate the behavior of specific populations of c
hains. It was revealed that chains with the highest level of tacticity crys
tallize first, as is expected, and strongly influence the subsequent crysta
llization of the remaining chains. In addition, evidence of cocrystallizati
on between the solvent fractions was observed.