Evidence for a mechanically active high temperature relaxation process in syndiotactic polypropylene

Frequency- and temperature-dependent dynamic mechanical tests on syndiotactic-polypropylene (s-PP) show the existence of a relaxation process at the high temperature or low frequency-side of the dynamic glass process. Its frequency is about 10−1 Hz at 100 °C and varies with temperature in an unusual manner, non-Arrhenius like, with an upward curvature with increasing temperature. The blocky substructure found for the crystalline lamellae of s-PP and the strain control of the deformation behavior, which needs more degrees of freedom than offered by stacks of internally stiff crystal lamellae, favors the assignment of the new process to intralamellar block slips. The assignment finds support in the observed retardation of the process accompanying a crystal thickening and the isotropy of the associated mechanical relaxation strength in an oriented sample.