Models for molecular motions within polymer chains. Part 1. A solid-state NMR study of hexane-1,6-diyl bis(p-nitrobenzoate)

Solid-state NMR experiments on hexane-1,6-diyl bis(p-nitrobenzoate) and its 1,1,6,6- and 2,2,5,5-deuteriated derivatives present a coherent view of the molecular dynamics of the central alkyl chain. The techniques used include C-13 CP/MAS spectra, H-2 quadrupole echo spectra, associated with measurements of C-13 T-1 rho relaxation times, H-2 and C-13 T-1 relaxation times and quadrupole echo reduction factors. Molecular dynamics in the central chain are dominated by librational motions at the CH2 groups that can best be approximated by a six-site conical model. The activation energies for these librations are ca. 35 kJ mol(-1). gauche-trans flips in the chain can be ruled out as the origin of the effects observed.