Component relaxation processes within elastomeric polypropylene

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.