The thermal imidization process of 1,2,4,5-benzenetetracaboxylic (PMDA)/4,4'-diamnodiphenyl ether (4,4'-ODA) solutions in N-methyl-2-pyrrolidone (NMP) from polyimide (PI) precursor, poly (amic acid) (PAA), was systematically investigated through a series of characterization methods, such as Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). At the low-temperature drying stage, mechanical properties and T-g of polymer films were increased as a result of solvent removal. TGA method was used to quantitatively monitor the evaporations of hydrogen-bonded solvents on PAA and of the dehydration during the imidization reaction that occurred above 150 degrees C. During the imidization stage, the interplay between the solvent evaporation and the imidization was the key factor that determined the enhancement of the mechanical properties and T-g. The degree of imidization approached 94% when the temperature was increased to 250 degrees C. A "complete" imidization was achieved by annealing between 350 and 400 degrees C. The enhancement in the mechanical properties of final PI films may result from the increased T-g and the crystallized structure formed during the annealing stage. (C) 2016 Elsevier Ltd. All rights reserved.