Polyaminotriazines represented by formula (I) can be prepared by conducting a reduction alkylamination of a tetramethylpiperidone with a diamine represented by formula (IIb), NH2—R—NH2, in the presence of a hydrogenating catalyst, removing the catalyst upon completion of the reaction to obtain an unrefined crude product (A); and, conducting a polycondensation reaction of the unrefined crude product (A) and a dichlorotriazine in an aromatic solvent and in the presence of an inorganic base.