SIDE-CHAIN MOTION AND STRUCTURE OF RACEMIC POLY(GAMMA-BENZYL GLUTAMATE) AS STUDIED BY SOLID-STATE HIGH-RESOLUTION C-13 NUCLEAR-MAGNETIC-RESONANCE

The side chain motion and structure of the racemic mixture of poly(gamma-benzyl glutamate) (PBDLG) in the solid state were studied by means of the cross polarization/magic angle spinning (CP/MAS) C-13 NMR. C(beta) and C(gamma) regions of NMR spectra for PBDLG in the stacked state of phenyl rings exhibit a remarkable difference from those for poly(gamma-benzyl L-glutamate) (PBLG) with no side chain stacking. Use of gamma-d2 PBDLG, deuterated at C(gamma), showed that the upfield shift occurs in a part of gamma-carbons. It was suggested that this new peak arises from the regular side chain conformation with phenyl ring stacking. The measurements of C-13 T1rho, spin-lattice relaxation time in the rotating frame, indicated that both the side chain and main chain motions are restricted in the stacked state. However, it is noticeable that such effect of stacking is especially remarkable for C(gamma) rather than phenyl ring. This means that phenyl rings have a rather high mobility even in the staked state.