CHARACTERIZATION OF POLYIMIDES BY C-13 AND H-1 SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE

The polyimides LaRC-TPI, LaRC-IA and LaRC-SI and related model compoun ds were investigated using C-13 and H-1 nuclear magnetic resonance (NM R). Magic angle spinning was used to acquire C-13 isotropic chemical s hift spectra of these materials. The spectra were assigned as complete ly as possible. In addition, the principal components of some shieldin g tensors were measured using variable angle correlation spectroscopy (VACSY). Of those studied, LaRC-SI is the only polymer that is soluble . However, after it is heated past its glass transition temperature, L aRC-SI becomes insoluble. Experiments were performed in an attempt to identify causes of this behavior. When magnetization from nuclei in ri gid regions of the polymer is suppressed, the H-1 and C-13 NMR spectra off soluble LaRC-SI are significantly different from those of insolub le LaRC-SI. Hydration studies of LaRC-SI show that absorbed water plas ticizes the polymer. (C) 1998 Elsevier Science B.V. All rights reserve d.