Imide oligomers having internal acetylene units in the backbone

Imide oligomers having internal acetylene groups in the backbone were prepared utilizing bis(3-aminophenyl)acetylene as an internal acetylene source. 2,2′-Bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenontetracarboxylic dianhydride (BTDA), and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) were used as acid dianhydride monomers. Amine-terminated oligomers with average degree of polymerization (DP) of 3, 5, and I 1 were prepared by controlling the ratio of monomers, and were end-capped with phthalic anhydride. Anhydride-terminated oligomers were similarly prepared and were end-capped with aniline. Imidization was conducted by refluxing in toluene. The DSC of the oligoimides containing internal acetylene units showed exotherm due to the crosslinking reaction of acetylene units. Onset temperature of the exotherm was 300–370°C, depending on the chemical structure and DP of oligoimide. By the thermal cure at high temperatures, the amount of exotherm decreased and exotherm shifted to higher temperature. Melt-processing of the oligoimides was carried out using a hydraulic press at 400°C. Melt-processed films were dark brown, opaque, and somewhat brittle. The films became less brittle with the increase of the DP of the oligomers. The films showed excellent thermal properties; T_g's were above 375°C, and their films maintained their mechanical properties aboveT_g.