Broadline n.m.r. studies of ultra-high modulus polyethylenes

Abstract

Broadline nuclear magnetic resonance (n.m.r.) measurements have been made for a range of isotropic and drawn high density polyethylene materials with different molecular weight distributions and three well defined thermal treatments during preparation. For the drawn materials the dependence of the n.m.r. spectra on the orientation of the static magnetic field with respect to the draw direction has been studied with respect to both line shape and second moment variation. The spectra in general show three component lines with distinctly different line widths. The broad component shows a high degree of molecular orientation in the drawn samples and can be satisfactorily assigned to the crystalline regions of the polymer. It is proposed that the intermediate component corresponds to high molecular weight molecules which interconnect the crystalline regions and are sufficiently constrained to allow motion about the chain axis only. This component shows an increasing degree of molecular orientation and decreases in intensity with increasing draw ratio. Finally, there is an isotropic narrow component, which is attributed to the mobile fraction. From its intensity in samples of different molecular weight this fraction can be associated with low molecular weight material and the ends of molecules which are rejected from the crystalline regions or the rigid fraction in a drawn sample.