MICROSCOPIC DYNAMICS AND MACROSCOPIC MECHANICAL DEFORMATION OF POLY(P-PHENYLENETEREPHTHALAMIDE) FIBERS

Deuterium NMR methods are used to characterize the dynamic structure o f PPTA [poly(p-phenyleneterephthalamide)] fiber as a function of tensi on. Spin-lattice relaxation results indicate that the high-frequency c omponent of the dynamic structure is not significantly altered by the fiber-spinning process or by the application of tensile stress to the fiber and as such does not differ from that of the as-polymerized poly mer. Quadrupolar-echo line shapes reflect the high degree of order as well as the motional heterogeneity of the fiber bundle. The applicatio n of a tensile stress equivalent to 55% of the breaking strength of th e fiber bundle alters the H-2 NMR line shape, thus reflecting the coup ling of macroscopic stress and microscopic dynamic structure through t he enhancement of the phenylene ring dynamics. Two-dimensional H-2 NMR methods are used to characterize the chain axis orientational distrib ution of a continuous fiber bundle. Simulations of the experimental sp ectra are consistent with a Gaussian distribution of orientations with a standard deviation of no larger than 5 degrees; this result is in g ood agreement with previous X-ray results and differs substantially fr om previous solid-state NMR approaches which utilized chopped fibers.