Crystal Structure and Packing Disorder of Poly(p-phenylenebenzobisoxazole):  Structural Analysis by an Organized Combination of X-ray Imaging Plate System and Computer Simulation Technique

Abstract

To clarify the crystal structure of poly(p-phenylenebenzobisoxazole) (PBO) fibers, the analysis has been made for the X-ray diffraction data collected by the imaging plate system in combination with the computer simulation technique. The characteristic features of the X-ray diffraction pattern of PBO fiber are seen in the spotlike equatorial reflections and the diffuse reflections along the layer lines. The peak positions of the diffuse layer-line reflections were found to fit well to those of the molecular transform calculated for a uniaxially oriented isolated chain, suggesting an appreciably low correlation in the relative height between the neighboring chains. Among many types of the energetically minimized crystal structural models constructed by a computer simulation technique, a model giving a good fit between the observed and calculated X-ray profiles was found, in which the chains are assumed to form the layers extending along the 110 planes with the relative heights of the adjacent chains in the sheets almost confined to either +c/4 or -c/4 (c ) fiber identity period) and these sheets are stacked together in the b-axis direction with random heights along the chain axis.

An investigation into the relationship between internal stress distribution and a change of poly‐ p ‐phenylenebenzobisoxazole (PBO) fiber structure

“…We will give further explanation on this problem in the last section. One theory to explain why the crystal lattice starts to distort may be the microslippage due to weak interaction forces of neighboring molecules in the PBO crystal, 10 the onset of which may come from structural defects such as chain ends and the amorphous region in the fiber. Jones and Martin 21 reported that the PBO fiber modulus strongly depends on the concentration of molecular ends in the PBO crystal, which may support the above discussion.…”

“…There have been many studies to elucidate the secrets of PBO mechanical properties and morphological features. [5][6][7][8][9][10][11] One of the important structural features is that the fiber is composed of rigid-rod molecules that are highly oriented to the fiber axis. This molecular orientation improvement is made possible by the dry-jet wet spinning method together with heat treatment over 600°C under tension.…”

A Novel Random Preferential Orientation of the Crystal A‐axis Along the Radial Direction Confirmed on the Poly‐<i>p</i>‐phenylenebenzobisoxazole (PBO) Fiber Made with a Water

“…The fiber can be spun from dope (concentrated solution) made from PBO molecules and poly-phosphoric acid, then coagulated, washed, dried and heat-treated if necessary. Because the PBO molecule take a relatively straight conformation in the fiber, the molecular orientation is proved to be very high along the fiber axis, whereas the interaction between molecules normal to the fiber direction is not so strong [4][5][6][7][8][9][10][11][12][13][14][15][16][17] . Therefore, the fiber shows relatively small crystallite size, especially along the a-and b-axes.…”

The Effect of Non-Aqueous Coagulation in the Structure of Poly-<i>p</i>-phenylenebenzobisoxazole (PBO) Fibers

“…To improve this mechanical properties much higher, we have been looking into the structural formation of fiber during coagulation and found that a non-aqueous coagulant gives a different fiber structure 1 . The fiber is expected to have a higher molecular orientation with less structural inhomogeneity along the fiber axis, which has been revealed by small and wide-angle X-ray diffraction (SAXS and WAXS) techniques and high-resolution transmission electron microscope (HREM) observation [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] . Figure 1 shows the relationship between fiber modulus and the crystallite orientation of the (200) diffraction of the PBO crystal estimated by X ray, in which the three fibers show high molecular orientation to the fiber axis than other conventional fibers 19 .…”