NMR spectra of systems with restricted motion: Cross-linked polymer gels

Abstract

Swollen cross-linked polystyrene, and a parallel solution of linear polystyrene in CCl 4, were studied by 1H NMR, both conventional and with magic angle rotation (MAR-NMR), and by 13C NMR lineshape, T 1 and NOEF. The 1H MAR-NMR spectra of the cross-linked polymer were found to be almost identical to conventional 1H NMR spectra of the linear polymer in a broad temperature range. Also, the 13C T 1 and NOE parameters were equal for the cross-linked and linear polymer indicating little difference in the dynamics of rapid internal motions. The characteristic “super-Lorentzian” lineshape of conventional 1H NMR spectra of the cross-linked polymer gel is analyzed in terms of a convolution of a residual dipolar broadening function G( ν − ν 0) with a narrow lineshape function S( ν − ν 0)defined by rapid internal motions.