15N NMR spectroscopy as a method for comparing the rates of imidization of several diamines

Abstract

The relative rates of the conversion of amide-acid to imide was measured for a series or aromatic diamines that have been identified as potential replacements for 4,4'-methylene dianiline (MDA) in high-temperature polyimides and polymer composites. These rates were compared with the 15 N NMR resonances of the unreacted amines. The initial rates of imidization track with the difference in chemical shift between the amine nitrogens in MDA and those in the subject diamines. This comparison demonstrated that 15 N NMR spectroscopy is appropriate for the rapid screening of candidate diamines to determine their reactivity relative to MDA, and can serve to provide guidance to the process of creating the time-temperature profiles used in processing these materials into polymer matrix composites.3

Cocoon-in-Web-Like Superhydrophobic Aerogels from Hydrophilic Polyurea and Use in Environmental Remediation

“…All other conditions were similar to those used for solid-state 13 C NMR. The assignment to dangling unreacted terminal aliphatic −NH 2 of the low-intensity 15 N resonance at 41 ppm (vs glycine- d 5 ) in the solid-state spectra of PUA aerogels, made in acetone and CH 3 CN, was based on the reported resonance of 1-hexylamine at −357.5 ppm and of 4,4′-methylenedianiline at −323 ppm vs CD 3 NO 2 . The degree of crystallinity of all PUA aerogels was determined using powder X-ray diffraction (XRD) with a PANalytical X′Pert Pro Multi-Purpose Diffractometer (MPD) with a Cu Kα radiation source (λ = 1.54 Å).…”