Pendent polyimides using mellitic acid dianhydride. II. Structure-property relationships for zirconium-containing pendent polymers

Using mellitic acid dianhydride to prepare Zr-containing pendent copolyimides (co-Pls) is currently being evaluated as a means of further increasing Zr concentration and atomic oxygen resistance while retaining other desirable film properties. The immediate objectives en route to this ultimate goal are: (1) to address the increased tendency of copolyamic acids (co-PAAs) to undergo gelation during polymerizations and upon addition of dicyclohexylcarbodiimide during the Zr appending reactions, and (2) for multilayer films, to increase the number of layers that can be applied prior to crack formation. To accomplish these two objectives, a targeted structure-property study has been performed, holding the Zr concentration constant at 10 mol %. The polymer starting materials chosen for this investigation include PMDA and OPDA (dianhydrides), and 4,4'-ODA, 3,4'-ODA, and 1,3-APB (diamines). The spectroscopic data for all polymer products are consistent with the expected amic acid, imide, pendent, and nonpendent structures. Thin-layer chromatography, viscosity, and gel permeation chromatography (GPC) results confirm the polymeric nature of the Zr pendent and nonpendent co-PAA precursors, with intrinsic viscosities (eta(0)) of 0.86-0.46 for the former and 0.76-0.38 for the latter. Weight-average molecular weights are estimated from GPC to be 115,400-436,000 g/mol for the former and 38,300-111,200 g/mol for the latter. While there was little observable effect of structure change on tendency to form gel, APB-containing Zr pendent copolyimide had the lowest glass transition temperature and allowed the largest number of layers to be cast in a single film without cracking (10 layers) of the pendent copolyimides in this study. (c) 2007 Wiley Periodicals, Inc.