Melt processable semicrystalline polyimide structural adhesive based on 1,3-bis(4-aminophenoxy)benzene and 3,3′,4,4′-biphenyltetracarboxylic dianhydride

Introducing crystallinity in polyimides offers the advantage of increased solvent resistance and retention of mechanical properties above the glass transition temperature(T-g). This work examines the thermal stability, semicrystalline morphology and adhesive properties of a new polyimide synthesized at Virginia Tech which is based on 1,3-bis(4-aminophenoxy) benzene (TPER diamine) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA). The polymer has a T-g of ca. 210 degrees C and a T-m of 395 degrees C. Polarized light microscopy was used to evaluate the morphology and spherulitic growth rates. The effects of molecular weight and melt conditions were studied in this regard. Lap-Shear specimens were made using Ti-6Al-4V alloy and the bonding conditions were optimized with respect to bonding temperature, bonding time and pressure. High lap-shear strengths of ca. 8000psi (55.172MPa) were obtained and the fracture surface investigation using the SEM revealed a very rough ductile surface. Durability studies on lap shears were conducted for aging and testing temperatures of ambient, 177 degrees C and 232 degrees C. Significant stability was observed far these aging temperatures for up to seven weeks. The bond strengths were found to be affected by testing temperatures rather than the aging conditions for the duration of the study. The effect of various solvents was investigated using lap-sheer tests for periods up to 9 days.