Orientational alignment in solids from bidimensional isotropic-anisotropic nuclear magnetic resonance spectroscopy: applications to the analysis of aramide fibers.
The use of two-dimensional isotropic-anisotropic correlation spectroscopy for the analysis of orientational alignment in solids is presented. The theoretical background and advantages of this natural-abundance 13C NMR method of measurement are discussed, and demonstrated with a series of powder and single-crystal variable-angle correlation spectroscopy (VACSY) experiments on model systems. The technique is subsequently employed to analyze the orientational distributions of three polymer fibers: Kevlar 29, Kevlar 49 and Kevlar 149. Using complementary two-dimensional NMR data recorded on synthetic samples of poly(p-phenyleneterephthalamide), the precursor of Kevlar, it was found that these commercial fibers possess molecules distributed over a very narrow orientational range with respect to the macroscopic director. The widths measured for these director distribution arrangements were (12 +/- 1.5) degrees for Kevlar 29, (15 +/- 1.5) degrees for Kevlar 49, and (8 +/- 1.5) degrees for Kevlar 149. These figures compare well with previous results obtained for non-commercial fiber samples derived from the same polymer.
Sachleben
J R
JR
Department of Chemistry (M/C III), University of Illinois at Chicago 60607-7061, USA.
Frydman
L
L
D016880:Anisotropy; D009682:Magnetic Resonance Spectroscopy; D011108:Polymers / Q000737:chemistry
D011108:Polymers