Analysis of cross-polarization dynamics between 1H and 19F in Viton fluoroelastomer using solid-state 19F magic angle spinning and 1H → 19F cross-polarization magic angle spinning NMR

✍ Scribed by Shinji Ando; Robin K. Harris; Gustavo A. Monti; Stefan A. Reinsberg

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 210 KB
• Volume: 37
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199910)37:10<709::aid-mrc524>3.0.co;2-g

✦ Synopsis

The cross-polarization dynamics between 1 H and 19 F in a Viton-type fluoroelastomer were studied using 19 F magic angle spinning (MAS) and 1 H ! 19 F 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 1 H and 19 F 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 T HF , T H 1 and T F 1 for five separate peaks in the 19 F spectra. The values of T H 1 and T F 1 obtained are consistent with those independently measured by spin-locking experiments. The true values of T HF 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 T F 1 and T F 1 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.