The orientation distribution in an industrial sample of poly(p‐phenylenetere‐phthalamide) determined by two‐ and three‐dimensional NMR techniques

Two new solid‐state NMR methods for measuring orientation distributions in partially ordered solids are applied to high tensile‐strength fibre polymers. Both methods use the anisotropy of the carbon‐13 chemical shift tensor as a probe for local molecular directions, but they differ in the manner in which the information is extracted and complement one other. The spectral resolution is higher in the ORDER (ORientation Distributions with Enhanced Resolution) experiment, which employs rotor‐synchronized three‐dimensional magic angle spinning (MAS) NMR, while the angular precision with which the orientation distribution can be determined is higher in the DECODER (Direction Exchange with Correlation of Orientation Distribution Evaluation and Reconstruction) experiment. The utility of the two techniques is demonstrated by their application to the study of industrially produced poly(p‐phenyleneterephthalamide) fibres. Both give the same result for the width (χ = 13°) and the order parameters ( =0.85, =0.57, =0.34, =0.14) of the orientation distribution.