Characterizationand Polymerization Kinetics of Triazine-BasedBenzoxazine Monomers: Effects of Pyridine and Bromine Interactions

In this work, we report the synthesis and comprehensive characterizations of two series of triazine-based benzoxazine monomers derived from trifunctionalized aniline (TA-TPh-3NH₂) and aminopyridine (TA-TPy-3NH₂) precursors. The benzoxazine monomers, both with and without bromine substitution, were prepared through sequential Schiff base formation, reduction, and Mannich condensation reactions. Structural elucidation was achieved via Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) calculations, reduced density gradient (RDG) analysis, and molecular electrostatic potential (MESP) mapping were performed to probe the electronic structures, noncovalent interactions, and hydrogen bonding influences in these systems. The incorporation of bromine was found to slightly modify the HOMO–LUMO energy gaps, reduce negative electrostatic potential values, and alter polymerization kinetics, as evidenced by dynamic DSC measurements and activation energy (<i>E</i>_a) determinations using the Kissinger and Ozawa methods. Overall, our results provide deep insights into how subtle changes in molecular structure, especially bromine substitution and the nature of the heterocycle, influence the thermal and chemical properties of these advanced benzoxazine monomers.