Synthesis and properties of processable polyimides containing diacetylene groups

Diacetylene-containing polyimides have been prepared by the oxidative coupling of new diethynyl diimide monomers. Condensation of various ethynyl-terminated amines with either 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) or pyromellitic dianhydride (PMDA) provided the monomers. Processability was enhanced by increasing the number of consecutive methylenes in the backbone, by incorporating aliphatic side chains, and for the 6FDA-based polyimides in general. The 6FDA-based diacetylene-containing polyimides are soluble in many common solvents including acetone. By controlling polymerization time, either oligomers or polyimides can be produced in high yield. High-resolution H-1 NMR and IR spectroscopy were used to monitor the polymerization. With the exception of the polyimides containing aliphatic side groups, thermal analysis reveals a diacetylene reaction exotherm that occurs without evolution of volatile byproducts; upon thermal annealing, the exotherm disappears and these polyimides become insoluble in all common solvents (i.e., cross-linked). Gas-transport properties are reported for one of the cross-linked 6FDA-based materials.