Synthesis and Thermal Cure of Anthracenyl−Ethynyl End-Capped Imide Oligomers

Abstract

The model compound, N-phenyl-4-(9-anthracenylethynyl)phthalimide (3), was synthesized and the thermal curing behavior analyzed. These results were compared to the curing kinetics of similar model compounds N-phenyl-4-(1-naphthylethynyl)phthalimide (1) and N-phenyl-4-phenylethynylphthalimide (2). The cure rates are found to increase in the order of phenyl < naphthyl ≪ anthracenyl with indistinguishable Ea values for 1 and 2. Compound 3 showed a slightly lower Ea for the curing process. The end-capping reagent 4-(9-anthracenylethynyl)phthalic anhydride (4-AnEPA, 4) was prepared and used to synthesize an “anthracenyl−ethynyl terminated imide oligomer” (AnETI-5) and a lower Tg anthracenyl−ethynyl terminated imide-co-oxydiphthalic anhydride oligomer (AnETI-5-ODPA). Kinetic data for the thermal cure of the oligomers were measured by monitoring the change in Tg and applying the DiBenedetto equation. To ensure consistency, the thermal cure kinetics of phenyl−ethynyl terminated imide oligomer (PETI-5), naphthyl−ethynyl terminated imide oligomer (NETI-5), and phenyl−ethynyl terminated imide-co-oxydiphthalic anhydride oligomer (PETI-5-ODPA) were co-analyzed. The Tg observed for the cured resins was found to be independent of the end-cap type. However, the new aryl−ethynyl end caps provide significant thermal cure rate acceleration, often without a change in the Ea. For example, the anthracenyl−ethynyl end-capped oligomers can be cured at the same rate as the phenyl−ethynyl analogue; however, at a temperature nearly 80 °C lower!