H-1 and C-13 solution NMR of polyimides based on 4,4 '-diaminotriphenyl methane: Conformational analysis using NOE and molecular modeling

H-1 and C-13-NMR spectra of a model compound and polyimides based on 4,4'-diaminotriphenylmethane were analyzed and assigned. NOE measurements in DNIF for a representative polymer were recorded and interpreted with the aid of conformational analysis. Results indicate that conformational forces in the polymer lead to the formation of a round-shape geometry along the polymer chain that comprises five repeating units. This finding is supported by the measured NOE's, which indicates proximity between nuclei that look far apart in the repeating unit. From molecular modeling and NOE's, internuclear distances were evaluated. Limitations of this approach are also discussed.