Magic Angle Spinning 13C NMR Studies of Filled Vulcanizates

Magic angle spinning (MAS) 13C NMR is investigated as an alternative method to IR spectroscopy of solution state NMR for the characterization of the elastomeric conmponents of filled vulcanizates. Good high resolution spectra can be obtained from standard. Bloch decays (i.e., without cross polarization) using magic angle spinning and high power decoupling. Although the peak resolution is not as good as in 13C spectra of comparable solubilized or pyrolyzed materials, the MAS spectra are of sufficient quality for polymer identification in simple filled vulcanizates in most cases. The MAS spectra are usable for direct quantitative analysis of the polymeric components without priot sample workup. A known series of filled cis-BR/SBR vulcanizates ranging from 0 to 100% SBR was examined. Direct analysis yielded results with an average absolute deviation of 1.2% from the expected values. A known series of NR cis-BR-SBR compounds which had been characterized previously by IR was also studied. The direct NMR analysts gave results comparable to those of the IR method. Use of a cis-BR/SBR standard curve derived from the previous cis-BR/SBR analysis improved the results for the triblend analyses. The MAS 13C NMR method has the advantage that a potentially suspect solubilization or pyrolysis step is eliminated. In many cases, results can be obtained in several hours. Also, results should not depend on degree of cure. The NR cis-BR/SBR results show that low levels of NR (∼3 to 5%) are detectable.