Adhesive properties of cured phenylethynyl-containing imides

As part of a program to develop structural adhesives for high-performance aerospace applications, work has continued on phenylethynyl-containing imides. Initial work on linear phenylethynyl-terminated imides (PETI), led to a material called LaRC(TM) PETI-5, which is now commercially available and was selected as the composite matrix resin and adhesive on the High Speed Research Program. In this report, the preparation and evaluation of a series of modified phenylethynyl-containing imides, which are being developed as secondary bonding adhesives, will be discussed. The modification of these materials compared with the linear material involves the use of a small amount of trifunctional monomer to introduce branching. These adhesives exhibit excellent processability at pressures as low as 15 psi and temperatures as low as 288 degrees C. The cured polymers exhibit excellent solvent resistance and high mechanical properties. Polymer properties can be controlled by varying the molecular weight, the amount of branching, and the phenylethynyl content. This research involves changing the flexibility in the copolyimide backbone of the branched, phenylethynyl-terminated adhesives and determining the effect on properties.