This disclosure relates to a process of purifying a polymer. The process includes (a) providing an organic solution containing a polyimide or polyamic ester in at least one polar, aprotic polymerization solvent; (b) adding at least one purification solvent to the organic solution to form a diluted organic solution, the at least one purification solvent is less polar than the at least one polymerization solvent and has a lower water solubility than the at least one polymerization solvent at 25° C.; (c) washing the diluted organic solution with water or an aqueous solution to obtain a washed organic solution; and (d) removing at least a portion of the at least one purification solvent in the washed organic solution to obtain a solution containing a purified polyimide or polyamic ester. This disclosure also relates to a process of preparing a film on a semiconductor substrate, as well as related purified polymer solutions, films, and articles.