Comparison of the axial correlation lengths and paracrystalline distortion for Technora and Kevlar aromatic polyamide fibers

X-ray fiber diagrams of the aromatic copolyamide Technora, prepared from terephthaloyl chloride and equimolar proportions of p-phenylenediamine and 3,4'-diaminodiphenyl ether, contain a series of nonperiodic layer lines that point to a structure consisting of parallel chains of random comonomer sequence. The meridional peak positions are predicted accurately for fully extended, infinite chains, and the observed and calculated peak intensities are also in reasonably good agreement. However, there is a less adequate match between the observed and calculated peak profiles, which are predicted to be very much sharper than those observed. The latter agreement is improved by using a model consisting of finite chain segments with a slightly nonlinear (sinuous) conformation. The best agreement for unannealed Technora is obtained with an ordered segment length of 300 +/- 15 Angstrom and sinuosity of g = 1.52 +/- 0.05%, where g is analogous to the index of paracrystalline distortion in a homopolymer structure. Very similar results are obtained for fibers that have been thermally annealed. These data are strikingly similar to those for Kevlar fibers(poly(p-phenylene terephthalamide)), for which the crystallite size along the fiber axis direction is 350 +/- 10 Angstrom with a paracrystalline distortion of 2.32 +/- 0.08% for Kevlar 29, increasing to 400 +/- 12 Angstrom with a paracrystalline distortion of 1.71 +/- 0.06% for Kevlar 149. Consequently, although Technora is a random copolymer and the presence Of the random diaminodiphenyl ether leads to a more distorted lateral packing of the chains than occurs in Kevlar, the fibers produced by the dry-jet wet-spinning process have extended conformations that are very similar in linearity to those for Kevlar, which probably account for the analogous high tensile strengths and moduli.