Synthesis and characterization of soluble phenylethynyl-terminated imide oligomers derived from pyromellitic dianhydride and 2-phenyl-4,4′-diaminodiphenyl ether

Novel addition-type imide oligomer (degree of polymerization: n = 1-10) derived from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 2-phenyl-(4,4′-diaminodiphenyl ether) (p-ODA) which has asymmetric and non-planar structure, and 4-phenylethynylphthalic anhydride was synthesized for the matrix resin of high heat resistant carbon fiber-reinforced composites. The uncured imide oligomers (degree of polymerization: n = 1-4) showed good solubility (more than 30 wt.%) in aprotic solvents such as N-methyl-2-pyrrolidone (NMP). These imide oligomers also showed a very low viscosity. These data were accomplished by preventing the aggregation caused by the pendant phenyl group of p-ODA. The imide oligomers were successfully converted to cross-linked structures after curing at 370 °C. The glass transition temperature and elongation at break (εb) of the cured imide resin were found to be very high (almost 360 °C and >15%) respectively.