Thermosetting Poly(imide silsesquioxane)s Featuring Reduced Moisture Affinity and Improved Processability

With the goal of improving the moisture resistance of thermosetting polyimides, a thermally stable, polyhedral oligomeric silsesquioxane (POSS) dianiline, which features an aromatic periphery, was co-oligomerized with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA), 4,4′-diaminodiphenyl ether (ODA), and phenylethynylphthalic anhydride (PEPA) to form thermosetting oligomers of a prescribed number of repeat units. The resultant oligomers were characterized for their chemical architecture, rheological characteristics, and cure behavior. POSS regioisomerism provided a unique opportunity to study the effects of monomer architecture on properties. The type of isomer affects rheological and cure characteristics but was found to have no discernible influence on cured state properties. The benefits of POSS co-oligomerization are 3-fold in that processability, thermal stability, and moisture resistance are each improved. Cured glass transition temperature is reduced, however, for a fixed number of repeat units, due to increased length and molecular weight between cross-links concomitant with POSS co-oligomerization.