Hemiaminal was synthesized using 4,4’-diaminodiphenylsulphone (DDS). The structural characterization of the material was carried out using Fourier transform infrared spectrometer (FTIR). It is noted that the presence of absorption bands pertaining to NMP and the identification of -OH stretching confirms the proposed structure for the hemiaminal compound. The curing characteristic of the material was investigated using differential scanning calorimeter (DSC). From the DSC studies, it was found that the hemiaminal after 200 °C showed a strong exotherm which may be associated to the degradation of the hexahydrotriazine produced. This fact is supplemented using thermogravimetric (TG) study. The synthesized material was thermally cured and the polymer structure was investigated using FTIR. The absence of absorption band around 3300 cm-1 in the polyhexahydrotriazine compound indicates the conversion of the hemiaminal to the hexahydrotriazine form through cyclization reaction. The thermal degradation behaviors of PHT material was investigated by thermogravimetric analyzer at three different heating rates (β = 10, 20 and 30 °C min-1). The most widely used integral methods like Flynn-Wall-Ozawa (FWO), Corrected Flynn-Wall-Ozawa (C-FWO), Kissinger-Akahira-Sunose (KAS), Corrected Kissinger-Akahira-Sunose (C-KAS), Vyazovkin (VYZ) and Advanced Vyazovkin (A-VYZ) methods are used to estimate the apparent activation energy for thermal degradation (Ea-D) of the material for various reaction extent (α). The results were presented and discussed.