Structure of poly (p-phenylenebenzobisoxazole) (PBZO) and poly (p-phenylenebenzobisthiazole) (PBZT) for proton exchange membranes (PEMs) in fuel cells

The structures of membranes of PBZO and PBZT extruded with counter rotating dies (CRD) were studied by wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), atomic force, scanning electron and transmission electron microscopy (AFM, SEM, and TEM). The structure of CRD-extruded PBZO was compared with that of a solution-cast membrane. The extruded membranes have sheet structures typical of rigid-rod polymers. The heterocyclic rings of the extruded membranes are oriented approximately parallel to the membrane surface, while those of the cast membrane are oriented perpendicular to the surface. The parallel orientation of the rings of the extruded membranes may be due to the normal force exerted during extrusion. The polymer molecules near the surfaces of the extruded membranes are oriented along the shear directions of the extruder, while those in the middle are oriented randomly. There is little cholesteric nature. These materials have potential as microporous PEMs holding ion conducting polymers (ICPs).