Side chain dynamics in poly(γ-benzyl l-glutamate) as studied by high-resolution solid state 13c nuclear magnetic relaxation in rotating frame

Abstract

The rotating frame 13C spin-lattice relaxation time for poly(γ-benzyl L-glutamate) (PBLG) in the solid state was measured by the cross polarization/magic angle spinning (CP/MAS) NMR. From the 13C spin-lock frequency dependence of ‘observed’ relaxation time T1ρ*, it was revealed that the spin-lattice process with a relaxation time T1ρ is dominant rather than the spin-spin process. Thus, T1ρ measurement gives the information about the dynamical behaviors in PBLG. The temperature dependence of T1ρ was investigated above room temperature. The T1ρ∼temperature curves for side chain carbons showed a minimum, whose value is much larger than the expected one for the isotropic motion with a single distribution of the correlation time. It was suggested that side chain motion is highly anisotropic and/or the distribution of the correlation time is excessively broad. However, the temperature causing such a T1ρ minimum is very close to that for previously reported β-process corresponding to motion of whole side chain. Further, T1ρ results showed that the motion of benzyl group at the end of side chain contributes dominantly to the β-process. The effect of MAS rate on T1ρ is briefly discussed. © 1993, The Society of Polymer Science, Japan. All rights reserved.