ESR observations on stretching-induced molecular mobility and partitioning among sites in polyethylene films

We report on an ESR study of spin-probe-doped semicrystalline low-density polyethylene films subjected to stretching in a unique direction. Typical ESR spectra, obtained from a variety of stable nitroxides located in the amorphous region of the polymer, classify into three categories associated respectively with dopants trapped between parallel chains with high orientational order, radicals dissolved in chain environments of random spatial distribution, and spin clusters. Our results inform on stretching-induced translational mobility and, thereby, redistribution of a formerly homogeneous spin population among the above-mentioned sites, with the absolute and relative solubilities determined by the nature of the probe molecule. Implications on the mechanisms of cold-drawing and on intermolecular solute-polymer interactions are inferred, and comparison with previous studies of this system is presented.