Morphology control of various aromatic polyimides by using phase separation during polymerization

Morphology control of various aromatic polyimides representative as poly(4,4′-oxydiphenylene pyromelliteimide) was examined by using the phase separation during solution polymerization. Polymerizations of aromatic dianhydrides and aromatic diamines to the polyimides were carried out in poor solvents at 240-330 °C for 6 h with no stirring. Polymerization concentrations were from 0.25% to 3.0%. The polyimides were obtained as yellow precipitates. Two categorized morphologies were created, which were particles and crystals exhibiting lath-like and plate-like habits. These morphologies of polyimides could be selectively controlled by the polymerization conditions. The higher concentrations, less miscible solvents and lower temperatures were preferable to yield the particles via liquid-liquid phase separation. On the contrary, the lower concentration, miscible solvents and higher temperature were desirable to yield the crystals. The polyimide precipitates showed high crystallinity and possessed excellent thermal stability at which the 10 wt% loss temperatures in N2 were in the range of 590-694 °C.