Polyamide terpolymer films can be obtained by the evaporation of a solvent-terpolymer-photoinitiator mixture on a glass plate. Through ultraviolet (UV) irradiation, self-developing properties are observed. The nuclear magnetic resonance (NMR) study of the photochemical reaction involved in such a process permits us to propose a mechanism with a diffusion of solvent in the irradiated areas. The thermodynamics of irreversible process have been applied to the analysis of such a system behavior, and an analysis of the stability of the system resulting from its residual solvent content has been made.