SPINNING AND CHARACTERIZATION OF FIBERS FROM POLY(2,6-DICHLORO-P-PHENYLENETEREPHTHALAMIDE) - A STUDY OF CONSTITUTIONAL ISOMERISM AND SOLID-STATE ARRANGEMENTS BY COMPARISON BETWEEN SIMULATION AND EXPERIMENT

Fibers of three constitutionally isomeric rigid-rod polymers, produced by polycondensation of 2,6-dichloro-p-phenylenediamine and terephthal oyl dichloride, were spun from nematic solutions and characterized by wide-angle X-ray diffraction (WAXD) measurements and mechanical tests. A post-spin heat treatment was employed to improve the low degrees of orientation and crystallinity that the untreated fibers showed. The d ominating crystal structure of constitutionally ordered head-to-head/t ail-to-tail fibers seems to be very similar to ''Modification II'' of the fibers from poly(p-phenyleneterephthalamide) (PPTA), but the fiber s do not suffer a comparable structural transformation upon heat treat ment. Influences of the constitutional regularity in the chains on the crystal structure, structural order and mechanical properties of the fibers could be observed. Both the observed crystal structure and the experimentally determined mechanical properties agree well with the re sults of detailed atomistic modeling predictions.