Spin lattice relaxation in linear polyethylene

Abstract

The 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.