N‑Activated 1,3-Benzoxazine Monomer as a Key Agent in Polybenzoxazine Synthesis

A novel and successful
application of ring-closing reactions of
aminophenols has been proposed for the formation of a new type of
1,3-benzoxazine ionic derivatives. The optimization of the reaction
and detailed computational studies have been reported for the estimation
of heterocyclic ring stability and its further transformation, which
is crucial in the polymerization process. The molecular structure
of the obtained compounds has been fully characterized by applying
X-ray analysis and spectroscopic methods. The novel benzoxazines undergo
an intriguing thermal reaction leading to classical benzoxazines and
chloroalkanes, which is the first step of transformation before polymerization.
To gain more insights into the transformation behavior of ionic benzoxazine
derivatives, the Fourier transform infrared (FT-IR) spectra of gaseous
products were recorded in experiments with near simultaneous FT-IR/TGA
measurements. The combination of thermogravimetry with FT-IR spectroscopy
enables the quantitative and qualitative characterization of thermal
transformation products and clarification of the reaction mechanism.
The experimental data have been verified by applying DFT­(B3LYP) and
DFT­(M062x) theoretical studies.