New adhesives: Bismaleimide liquid crystals containing polymethylene flexible groups and aramide–arylate mesogen groups

Four adhesives (one adhesive BEA 811 and three adhesives BENDA 811) containing new bismaleimide (BMI: B 8 and B 11) with aramide/arylate and polymethylene as mesogen and flexible groups, respectively were studied. Starting from the BMIs, eutectic mixture BE 811 was developed. It presents low melting temperatures (153.4 °C) and crosslinks giving liquid crystal ordered state. The new adhesives have been prepared by mixing the original BMIs (eutectic mixture of B 8 and B 11: BE 811) with other compounds usually used in the formulations of composite materials and structural adhesives. Adhesive formulations of BEA 811, mixture BE 811 and DABA, and BENDA 811, mixture BE 811, DABA and NOVOLAC, crosslink generating an ordered state as well. The relation between structure, thermal properties and breaking force was investigated. Subsequently, these mixtures were tested as iron–iron adhesives. Finally, aging tests were achieved, in both laboratory and in-situ environments (in Vietnam and Morocco). The high performances of thermoset adhesives (BENDA 811 and BEA 811), compared to industrial polyimide adhesive (MATRIMIDE 5292), were attributed to molecular structures and their crosslinking ability in the liquid crystal state.