Supramolecular functionalized polybenzoxazines from azobenzene carboxylic acid/azobenzene pyridine complexes: synthesis, surface properties, and specific interactions

Abstract

In this study we synthesized Azo-COOH BZ, a new benzoxazine derivative containing both azobenzene and carboxylic acid units, through the reaction of 4-(4-hydroxphenylazo)benzoic acid (Azo-COOH, itself prepared through a diazonium reaction of 4-aminobenzoic acid with phenol in the presence sodium nitrite and NaOH) with paraformaldehyde and aniline in 1,4-dioxane. Fourier transform infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance spectroscopy confirmed the chemical structure of Azo-COOH BZ. We used differential scanning calorimetry (DSC), thermogravimetric analysis, and FTIR spectroscopy to investigate the curing behavior of this new benzoxazine monomer. DSC revealed that the exothermic peak representing the ring opening polymerization of the benzoxazine unit appeared at low temperature relative to those of typical benzoxazines, indicating the presence of the carboxylic acid and azobenzene units of this monomer catalyzing the benzoxazine ring opening reaction. In addition, blending with various molar ratios of a benzoxazine monomer presenting a pyridyl unit (Azopy BZ) led to strong intermolecular hydrogen bonding between the CO₂H group of Azo-COOH BZ and the pyridyl group of Azopy BZ. These supramolecular complex systems also featured significantly lower curing temperatures (down from ca. 200 °C of Azo-COOH BZ to 150 °C of supramolecular complex), with their products retaining the high water contact angles required for low-surface-energy applications.