Morphological architecture of poly(p-oxybenzoyl) by modification of oligomer end-group

Influence of oligomer end-group on morphology of poly(4-oxybenzoyl) (POB) was examined by polymerizations of 4-acyloxybenzoic acids having different acyl groups. Polymerizations of 4-propionyloxybenzoic acid, 4-hexanoyloxybenzoic acid, 4-octanoyloxybenzoic acid and 4-decanoyloxybenzoic acid in liquid paraffin at 320 °C yielded needle-like or pillar-like POB crystals via crystallization of oligomers. On the other hand, the polymerization of 4-perfluorooctanoyloxybenzoic acid (FOBA) afforded microspheres having needle-like crystals on the surfaces. At an initial stage in the polymerization, microspheres having smooth surface were formed via liquid–liquid phase separation of oligomers prepared from FOBA owing to the low miscibility of perfluorooctanoyl end-group. Thereby the phase-separation behaviour of oligomers changed from liquid–liquid phase separation to crystallization at a middle stage in the polymerization and then needle-like crystals were formed on the surface of the microspheres. Chemical structure of the oligomer end-group affected significantly the phase-separation behaviour of oligomers and ultimately the morphology of POB.