Melt‐processable thermosetting polyimide: Synthesis, characterization, fusibility, and property

To obtain a melt‐processable thermosetting polyimide having a high glass‐transition temperature ( T g ) and good solvent resistance, the effect of introducing a crosslinkable agent into the polymer chain ends of the melt‐processable polyimide on its physical properties was studied. The polyimide (calculated number‐average molecular weight ( M n ) = 11,600 g/mol) capped with the crosslinkable agent exhibited poor melt flowability because its crosslinkable agent reacted at the processing temperature of 360 °C. To reduce the rate of crosslink reaction, two methods were investigated. One was lowering the processing temperature, and the other was decreasing the amount of crosslinkable agent. The low‐molecular‐weight oligomer (calculated M n = 6300 g/mol) capped with the crosslinkable agent exhibited good melt flowability at the lower processing temperature of 340 °C where the crosslinkable agent did not react. However, the obtained molded part of this oligomer was too brittle to maintain its shape. However, the polyimide (calculated M n = 11,600 g/mol) partially capped with the crosslinkable agent demonstrated good melt flowability at the processing temperature of 360 °C. Furthermore, the molded part of this resin was strong and tough. In addition, the cured part exhibited high T g and good solvent resistance.