Morphology control of polyimides by using phase separation during polymerization

Polyimides are useful high-performance plastics, and their properties are strongly influenced by the morphology including molecular orientation The morphology control of polyimide is required to create structural materials and devices. This study provides the new procedure to control the morphology by using oligomer phase separation during solution polymerization in poor solvents. When the molecular weight of the oligomers exceeds a critical value, the oligomers are phase-separated through super-saturated state. If they are precipitated via crystallization, the crystals having high molecular weight are formed by the subsequent solid-state polymerization in the crystals, for instance, lozenge-shape crystals of poly(p-phenylene pyromelliteimide) (PPPI) and lath-like crystal of Kaptoa On the other hand, when they are precipitated via liquid-liquid phase separation, the microspheres of PPPI and other polyimides are obtained. The miscibility between oligomers and solvents is an important parameter to control the morphology.