TEREPHTHALAMIDE RING DYNAMICS OF POLY(P-PHENYLENETEREPHTHALAMIDE)

The dynamics of terephthalamide rings in poly(p-phenyleneterephthalami de) (PPTA) are examined with H-2 NMR spectroscopy, and a description o f motion at this site is developed in conjunction with crystallite siz e information from X-ray diffraction data, thermal expansion data, and H-2 NMR results for the amide and p-phenylenediamine ring sites. Spin -lattice relaxation results for the terephthalamide rings differentiat e those sites in proximity to non-hydrogen-bonded amide sites on cryst allite surfaces from those sites near hydrogen-bonded amides on both t he crystallite surfaces and interior. The evolution of the fraction of terephthalamide rings which execute a pi-flipping motion as a functio n of temperature reflects the dynamic heterogeneity at this site; this process is reflective of not only the proximity of mobile amide sites on the crystallite surface but also the extent of structural imperfec tion.