Nuclear magnetic relaxation study of solid sulfolan

Sulfolan has been studied by pulsed NMR measurements of laboratory frame spin–lattice relaxation T1 and rotating frame spin–lattice relaxation times T1ρ in the temperature range from 186 to 339 K. The previously reported phase transition at 288 K has been observed, but the data also show the presence of two additional, as yet unreported, phase transitions. The two crystalline phases are characterized by twofold rotations of the sulfolan molecules while the two plastic phases are both characterized by isotropic rotation and translational diffusion. It is suggested that the lower temperature plastic phase involves monovacancy diffusion while the higher temperature one involves relaxed vacancy diffusion. The relaxation times at most temperatures in the solid phases are dependent on the previous thermal history of the sample, with the transitions being sluggish and displaying hysteresis effects.