This work investigates the thermal polymerization process of a methylene diphenyl diisocyanate (MDI) monomer as well as its thermal degradation following the ICTAC recommendations. MDI monomer is widely used as a synthetic resin in the production of MDF panels, as it provides compaction of the eucalyptus fibers by polymerization. Thermogravimetry/ derivative thermogravimetric-differential thermal analysis (TG/DTG-DTA), differential scanning calorimetry, and midinfrared spectroscopy were used in this study. The polymerization process (An) and degradation (Fn) process exhibited activation energy equal to 149.70 and 80.22 kJ mol-1 , respectively. The combined the FTIR and kinetic information makes it possible to suggest the mechanism reaction, which is an inedited data in literature.