SIDE-CHAIN DYNAMICS IN POLY(GAMMA-BENZYL L-GLUTAMATE) AS STUDIED BY HIGH-RESOLUTION SOLID-STATE C-13 NUCLEAR MAGNETIC-RELAXATION IN ROTATING FRAME

The rotating frame C-13 spin-lattice relaxation time for poly(gamma-benzyl L-glutamate) (PBLG) in the solid state was measured by the cross polarization/magic angle spinning (CP/MAS) NMR. From the C-13 spin-lock frequency dependence of 'observed' relaxation time T1rho*, it was revealed that the spin-lattice process with a relaxation time T1rho is dominant rather than the spin-spin process. Thus, T1rho measurement gives the information about the dynamical behaviors in PBLG. The temperature dependence of T1rho was investigated above room temperature. The T1rho approximately 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 T1rho minimum is very close to that for previously reported beta-process corresponding to motion of whole side chain. Further, T1rho results showed that the motion of benzyl group at the end of side chain contributes dominantly to the beta-process. The effect of MAS rate on T1rho is briefly discussed.