ON THE THEORY OF NMR LINE-SHAPES IN AMORPHOUS REGIONS OF UNIAXIALLY ORIENTED POLYMERS

A theory of NMR of protons belonging to highly-stretched polymer chain s with fixed ends, e.g. tie molecules of amorphous regions of oriented semicrystalline polymers, is presented. Analysis is carried out in te rms of the model of freely-jointed chains. All contributions to the li ne shape from the intramolecular dipole-dipole interactions (DDI) are taken into account. Expressions are derived for the residual time inde pendent component of DDI and the second moments of the fluctuating DDI . The NMR spectra are described in terms of the Anderson-Weiss approxi mation. A number of spectra are calculated for polyethylene. It is sho wn that the linewidth of high temperature spectrum rapidly grows with stretching and approaches that of crystallite polymer. It is demonstra ted that the distribution function of tie molecules can, in principle, be obtained from the dependence of the spectra on the stretching rati o.