Nuclear magnetic relaxation in polypropylene

Abstract

Nuclear magnetic resonance T₁, T_1ρ, and T₂ relaxation results are reported for drawn polypropylene. The results indicate that three relaxation processes are operative: a low-temperature methyl relaxation process, a higher temperature β relaxation, and a high temperature α relaxation process. The data presented here are consistent with previous interpretations of the first two relaxations. Little anisotropy was observed in the relaxation times when recorded as a function of the applied magnetic field direction. A theoretical expression for the rotating-frame relaxation time, T_1ρ, is derived which is appropriate to a rotation of the methyl group about its threefold axis. The effects of a distribution of relaxation times which result from a random orientation of methyl groups in the polymer are included as also are the effects of spin diffusion. The agreement between theory and experiment is satisfactory.