Chapter 20: Development of Sulfur-33 Nuclear Magnetic Resonance for Structural Study of Crosslinked Rubber

In this chapter, toward understanding crosslinked structures in rubbers, development of the solid-state sulfur-33 (³³S) nuclear magnetic resonance (NMR) method for analysis of organosulfur compounds and ones forming covalent bonds, which conventional NMR techniques may not be able to cover, is presented. Three methods to deal with large quadrupolar interactions of ³³S nuclei are briefly discussed, including (1) zero-field solid-state ³³S NMR, i.e., nuclear quadrupolar resonance (NQR), (2) frequency-swept solid-state ³³S NMR at lower magnetic field and (3) field-swept solid-state ³³S NMR. Among them, field-swept solid-state NMR has tremendous potential to observe a ³³S NMR signal of sulfur atoms involved in crosslinked structures in rubbers. This is because it can readily combine with the following two ultra-high sensitivity techniques; optomechanical NMR, in which an NMR signal can be converted into a laser having high sensitivities via micro-electro mechanical systems (MEMS) equipped with thin-film capacitor, and high-temperature superconducting (HTS) coil, in which the high-quality factor of Q (Q-factor) of more than 16 000 for the coil is achieved at the present time.