Novel phenylethynyl-terminated PMDA-type polyimides based on KAPTON backbone structures derived from 2-phenyl-4,4′-diaminodiphenyl ether

Novel phenylethynyl-terminated addition-type imide oligomers (degree of polymerization, n=4) derived from 1,2,4,5-benzenetetracarboxylic dianhydride, 2-phenyl-4,4′-diaminodiphenyl ether (p-ODA), which has an asymmetric and nonplanar structure, and 9,9-bis(4-aminophenoxy)fluorene were synthesized for use as the matrix resin of fiber-reinforced composites with high heat resistance. The uncured imide oligomers showed good solubility (>30 wt%) in aprotic solvents such as N-methyl-2-pyrrolidone and very low minimum melt viscosity. These excellent properties were achieved using steric hindrance of the pendant phenyl group of p-ODA in a solution or a melted state to prevent the intramolecular/intermolecular interactions of imide oligomer chains. The imide oligomers were converted to crosslinked structures after curing at 370 °C for 1 h. Thermal and rheological properties of the cured resins were characterized by differential scanning calorimetry, thermogravimetric analysis and dynamic rheometry. The glass transition temperature and elongation-at-break of the cured imide resin were found to be almost >350 °C and >15%, respectively. These excellent properties of pyromellitic dianhydride-based and p-ODA-based addition-type aromatic polyimides are promising for applications in highly heat-resistant composites.