Side Chain Motion and Structure of Racemic Poly(γ-benzyl glutamate) as Studied by Solid State High-Resolution 13C Nuclear Magnetic Resonance

Abstract

The side chain motion and structure of the racemic mixture of poly(γ-benzyl glutamate) (PBDLG) in the solid state were studied by means of the cross polarization/magic angle spinning (CP/MAS) 13C NMR. Cβ and Cγ regions of NMR spectra for PBDLG in the stacked state of phenyl rings exhibit a remarkable difference from those for poly(γ-benzyl L-glutamate) (PBLG) with no side chain stacking. Use of γ-d2 PBDLG, deuterated at Cγ, showed that the upfield shift occurs in a part of γ-carbons. It was suggested that this new peak arises from the regular side chain conformation with phenyl ring stacking. The measurements of 13C T1ρ, 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 Cγ rather than phenyl ring. This means that phenyl rings have a rather high mobility even in the staked state.