Chemically (phase-resolved) measurements were performed on a Bruker Avance III (Germany) spectrometer with a magnetic field strength of 9.4 T which corresponds to a resonance frequency of 400 MHz. A 1 mm thick rubber ring (3 mm outer diameter and 2 mm inner diameter) was packed at the center of a 4 mm zirconia rotor with a Vespel ® rotor cap. The sample was held in position by polytetrafluoroethylene spacers on either side. A Bruker BVT 3000 temperature controller was used for measurements at 80±0.1 °C. The 90° pulse corresponded to a length of 2.5 µs at a pulse power of 54 W.