NMR Absorption in Teflon Fibers

Nuclear magnetic resonance absorption in oriented polytetrafluoroethylene fibers has been investigated in the temperature range 170°–380°K. The sample, in the form of a parallel bundle of fibers, showed a marked dependence of line shape on the direction of the applied magnetic field over the temperature range studied, although the observed anisotropy was much greater above 285°K than below. Changes occurring in the linewidth and second moment at around 285°K indicate a rotational disorder transition in the crystalline regions of the polymer, and serve to illustrate the advantages of using oriented fibers in the NMR investigation of semicrystalline polymers.