Pendent Polyimides using Mellitic Acid Dianhydride. I. An Atomic Oxygen-resistant, Pendent 4,4′-ODA/PMDA/MADA Co-polyimide Containing Zirconium

Abstract

The goal of this research is to increase the metal-organic concentration in Kapton-like polyimides (PIs) to achieve increased atomic oxygen (AO) resistance while retaining desirable film properties. Co-polyamic acid (PAA) precursors were prepared using a novel polymer building block, mellitic acid dianhydride (MADA), to provide sites for pendent group attachment. Attachment of an amino group-functionalized zirconium complex to the co-PAA precursors was facilitated by a stoichiometric amount of dicyclohexylcarbodiimide. The viscous solutions which resulted were characterized by thin layer chromatography (TLC), viscosity, and gel permeation chromatography (GPC), or treated with excess poor solvent to precipitate powder samples, or cast onto glass slides and heated to produce imidized films. Powder samples were dissolved in deuterated solvent for proton nuclear magnetic resonance analysis, or characterized by thermogravimetric analysis and differential scanning calorimetry. Film samples were characterized by Fourier transform infrared and by scanning electron microscopy (SEM) before and after exposure to atomic oxygen in a plasma asher. The spectroscopic data are consistent with the expected amic acid and imide, pendent and non-pendent structures. TLC, viscosity and GPC results confirm the polymeric nature of the pendent and non-pendent co-PAA precursors, with inherent viscosities (<0)of 0.76 and 0.65 and weight average molecular weights (Mw) estimated to be 61 000 and 138 000 Dalton, respectively. As expected, visual and SEM inspections of pendent and non-pendent co-PI films reveal extensive surface roughening upon exposure to AO, with the former developing a white surface layer known from model compound studies to be predominantly zirconium dioxide. Additional reports describing the effects of polymer structure and pendent group concentration on film properties and AO resistance are in preparation.

Pendent polyimides using mellitic acid dianhydride. III. The effect of pendent group functionality on polymer properties

“…However, a significant decrease in film quality was observed even at relatively low additive concentrations. To address this limitation, the structures of the PAAs52–54 and of one of the additives49 were modified so that they could be covalently attached, i.e., the metal‐organic additive would now be a pendent group. As a result, substantial increases in the metal‐organic mole percentage became possible (up to 50 mole percent) while retaining good film quality 52.…”

“…All starting materials and solvents were obtained from sources, handled, and purified as described previously 52–54. MADA was prepared and its purity established by thermogravimetric analysis (TGA) as reported previously 54.…”

“…All starting materials and solvents were obtained from sources, handled, and purified as described previously 52–54. MADA was prepared and its purity established by thermogravimetric analysis (TGA) as reported previously 54. The nonfunctionalized pendent group precursor (4‐amino‐ N , N ′‐disalicylidene‐1,2‐phenylenediaminato)( N , N ′‐disalicylidene‐1,2‐phenylenediaminato)zirconium(IV), Zr(adsp)(Rdsp) where R = H, and all functionalized precursors were prepared as previously reported 49, 57.…”

“…Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), TGA, differential scanning calorimetry (DSC) (all samples analyzed twice), gel permeation chromatography (GPC) in 0.02 M LiBr/NMP (performed at the NASA Langley Research Center), oxygen plasma ashing, and scanning electron microscopy data were obtained as before 52–54. GPC was conducted with both a DRI and a differential viscosity (DV) detector.…”

“…GPC was conducted with both a DRI and a differential viscosity (DV) detector. Polymer film samples were prepared, imidized, and evaluated (crack formation, creasibility, solvent resistance and atomic oxygen resistance) as described previously 52–54…”