Analysis of cross-polarization dynamics between1H and19F in Viton fluoroelastomer using solid-state19F magic angle spinning and1H →19F cross-polarization magic angle spinning NMR

Abstract

The cross-polarization dynamics between 1H and 19F in a Viton-type fluoroelastomer were studied using 19F magic angle spinning (MAS) and 1H → 19F cross-polarization (CP)/MAS NMR at 188.29 MHz. The phenomenological theory of spin thermodynamics based on the spin temperature hypothesis was employed to describe the polarization transfer between the 1H and 19F spin baths. Simultaneous fitting of the evolution of magnetization in the standard CP and a modified CP(TORQUE) experiment, using the exact solutions of the equations for the spin thermodynamics, gave unique sets of the parameters THF, and for five separate peaks in the 19F spectra. The values of and obtained are consistent with those independently measured by spin-locking experiments. The true values of THF are significantly larger (by a factor of ca. 4) than those derived from a simple two-parameter fit of the CP behaviour with variable contact time.The temperature dependences of and were measured between −49 and 86 °C. The relationship between the CP dynamics parameters and the local molecular motion in the polymer chains is discussed. Copyright © 1999 John Wiley & Sons, Ltd.