Characterization of cross-linked natural rubbers by proton longitudinal and rotating-frame relaxometry

A series of rubbers has been investigated in the 1–100 kHz range by proton relaxometry (measurement of the nuclear relaxation rate as a function of the amplitude of the magnetic field along which nuclear magnetization is aligned: the static field B0 for the longitudinal rate R1, the radio-frequency field B1 for the rotating-frame rate R1ρ). Data can be interpreted according to Ri=ai+bi/ναi, where ν0,1=γB0,1/2π (γ being the gyromagnetic ratio), the index i characterizing the sample as well as the nature of the relaxation parameter (longitudinal or rotating-frame). ai and bi are related to residual dipolar couplings and thus afford the possibility of material discrimination.