The extent and types of changes occurring to polyaniline (PANI) films cast from solutions containing a gel inhibitor were characterized by solid-state NMR (SSNMR), Two secondary amine gel inhibitors, 2-methylaziridine (2-MA) and pyrrolidine (Py), were studied and observed to have very different reactivities with the polymer. C-13 and N-15 SSNMR data show that pyrrolidine adds to the quinoid ring of similar to50% of the repeat units, converting these units from the emeraldine base form to the leucoemeraldine form. The presence of the pendant amine group also disrupts chain packing, increasing the amount of kilohertz regime chain motion in the solid state as determined from the magnitude of T-1p(H). In contrast, 2-MA reacted only slightly with PANI, addition to similar to5% of the repeat units, but 0.72-MA/repeat unit was physically trapped in the PANI film. The greater reactivity of Py (pK(b) = 3) relative to 2-MA (pKb = 6) is related to the amine's nucleophilicity and orbital arrangement.