STUDY OF MOLECULAR MOBILITY IN ULTRAORIENTED POLYPROPYLENE BY THE SPIN-PROBE TECHNIQUE

The rotational mobility of nitroxide radicals in polypropylene samples with draw ratios varying from 1 to 18 has been studied between 30 and 110 degree C by the ESR technique. The drop in the rotational frequency with increasing orientation correlates very well with the behavior of various other measures of molecular mobility such as organic vapor sorption, proton spin-spin relaxation times from NMR, and dynamic mechanical loss factor. This implies that each of these parameters is a good indicator of the amount of free volume in the amorphous regions. Annealing at high temperature relaxes the amorphous chain segments, thereby increasing the spin-probe rotational frequency in the drawn samples to values even higher than that in the quenched isotropic material.