Incorporation of Multifunctional Polar Groups into Thermoset Polyimide Films for Heat-Resistant Adhesive Applications

Developing high-temperature polyimide (PI) adhesives requires the simultaneous enhancement of bulk cohesive strength and interfacial adhesion. In this work, a 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA)/4,4′-oxidianiline (ODA)-based phenylethynyl-terminated PI system was modified via a 30k/8k molecular weight blend strategy to prepare processable, self-supporting adhesive films. To enhance performance, three distinct polar diamines (sulfone, amide, cyano) were introduced to replace a portion of the ODA. This strategy aimed to strengthen substrate wetting for improved interfacial adhesion and to reinforce bulk cohesion through hydrogen bonding. It is confirmed that the amide-containing sample (PI-A50) was the most effective, showing the highest polarity with a dielectric constant of 3.9 and the highest total surface energy of 51.87 mJ/m2. It has also maintained excellent thermal stability, with a glass transition temperature (Tg) of 317 °C and a temperature at 5% weight loss (Td5%) of 537 °C. Molecular dynamics (MD) simulations revealed the unique synergistic mechanism for its superior performance. The –CONH– group not only showed a stronger interfacial binding energy with the Al (111) substrate, calculated at −19048.7 kcal/mol, but also formed the densest interchain hydrogen bond network, which explains why it achieved the highest cohesive energy density of 200.42 J/cm3 and the lowest fractional free volume of 44.28%. This simultaneous strengthening of both bulk cohesion and interfacial adhesion is the key to its enhanced performance.