The polymerization of N-phenylmaleimide (N-PMI) employing sodium phosphate tribasic as a catalyst has been successfully investigated in this study. The effect of dimethyl sulfoxide (DMSO) solvent on the principal catalyst, sodium phosphate tribasic, was extensively studied. The effects of several catalysts, including tetrabutylammonium acetate (TBAA), 4-dimethylaminopyridine (DMAP), Benzyl triethylammonium chloride (BTEAC), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO), 1-Methylimidazole (1MA) and potassium phthalimide salt on polymerization of N-PMI have been discussed in this study. Additionally, the kinetics of polymerization in DMSO with Na3PO4 as the initiator is investigated. By using 1H and 13C nuclear magnetic resonance (NMR) spectrum analysis, attenuated total Reflection-Fourier transform infrared (ATR-FTIR), the resultant polymers were identified. Thermogravimetric and differential scanning calorimetric analyses were used to study the thermal behaviors. Our results prove that a salt form of catalyst can initiate the polymerization of N-PMI in dimethyl sulfoxide at a suitable concentration and under favorable conditions