Grain boundary imaging by digital reconstruction of HREM lattice images of poly(P-phenylene benzobisthiazole) fibers

Abstract

Poly(p-phenylene benzobisthiazole) (PBT) is a rigid-rod polymer of interest for high-strength fibers and other applications including nonlinear optical behavior. PBT fibers are formed by coagulation into water from solutions of the molecule in strong acid. Because of the high orientation and strength of these fibers, the nature of boundaries and defects between crystalline regions is of particular scientific and technical concern.The crystal structure of PBT fibers has been investigated by electron and X-ray diffraction. It has been found that the unit cell is monoclinic with a =.59 nm, b =.36 nm, c =1.249 nm, gamma =95.5 degrees. The molecules are oriented along the c axis of the unit cell and exhibit axial translational disorder in both the [100] and [010] directions.PBT is resistant to electron beam damage, having a critical dose of 1.6 Coulombs/cm2 at 100 kV and room temperature.