Benzoxazines from piperazine-bridged BPA-alternative: Impact of complete phenolic blocking on polymerization

The design of polybenzoxazines from bisphenol alternatives with controlled curing pathways remains a challenge due to the rapid, multi-stage nature of cationic ring-opening polymerization (ROP). This study investigates the synthesis and thermal behavior of a novel piperazine-bridged bisbenzoxazine where all reactive sites on the phenolic core are blocked. Spectroscopic analyses (NMR and FTIR) confirm a complex competition between ring closure and retro-Mannich fragmentation during synthesis. DSC analysis and curing kinetics, evaluated using the Kissinger, Ozawa, and Friedman methods, revealed a profile consistent with a staged mechanism rather than classical benzoxazine curing. Accordingly, an initial formation of a kinetically trapped N,O-acetal network follows a limited amount of thermally triggered rearrangement. Moreover, TGA analysis revealed a low char residue, indicating that the N,O-acetal dominated network is highly susceptible to complete thermal volatilization via retro-Mannich reversal.