Spin lattice relaxation in linear polyethylene

Abstract

AbstractThe proton spin‐lattice relaxation times (T1) of linear polyethylenes (PE) of varying morphology were measured as a function of temperature. The T1 of oriented bulkcrystallized and solution‐crystallized material was isotropic, in disagreement with calculations based on a sample dipole pair model. Motion in the non‐crystalline regions of the samples is shown to be responsible for the T1 minimum occurring around −20°C. The dependence of T1 at the minimum on the long period reinforces the model of an amorphous fraction composed of disordered lamellar surface layers. The temperature of the T1 minimum and the dependence of T1 on the long period imply that the mobility of these amorphous regions is reduced in cold‐drawn and solution‐crystallized samples. This mobility irreversibly increases with annealing. In highly relaxed samples the motion of a small portion of the disordered regions is almost liquidlike, as indicated by the presence of a second shorter T1.