Dual Crosslinked Phenylethynyl End-Capped Sulfonated Polyimides via the Ethynyl and Sulfonate Groups Promoted by PEG

Typically, phenylethynyl (PE) end-capped oligomides require a temperature of 370 degrees C for 1 h to develop a crosslinked system. A published method using poly(ethylene glycol)s (DM-PEG-250 and PEG-400) as cosolvents with NMP was effective in crosslinking the ethynyl end-caps at 250 degrees C/3 h in nonsulfonated oligomides. The application of this novel crosslinked method to PE end-capped sulfonated oligomides was effective but caused a secondary crosslinked network via the sulfonic acid groups and ethylene glycol solvents. The solid-state C-13 NMR spectral data on C-13-labeled end-caps in the PE-3F-SPI-3 oligomide provide evidence for the ethynyl to ethynyl and ethylene oxide sulfonate ester dual crosslinked structure. Infrared spectroscopy of model compounds also provides evidence for the presence of crosslinked sulfonate ester and appended sulfonate ester side chains. C-13 NMR also provided quantitative data on the extent of the ethynyl to ethynyl crosslinking reaction and sulfonate ester crosslinks and side chains. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4476-4491, 2011