Synthesis and characterization of bio‐based benzoxazines derived from thymol

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Abstract
In the present study, bio‐based benzoxazine resins were synthesized from bio‐based phenolic compound; thymol, and three different amines; ethylamine, aniline and 1,6‐diaminohexane, and paraformaldehyde by solvent‐free condensation reaction. The chemical structures of bio‐based benzoxazines; T‐ea (thymol, ethylamine), T‐a (thymol, aniline), and T‐dh (thymol, 1,6‐diaminohexane) were characterized by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared (FTIR) spectroscopy, elemental analysis, and high‐resolution mass spectrometry. The curing studies of T‐ea, T‐a, and T‐dh bio‐based benzoxazines were performed by stepwise thermal treatment at 150, 175, 200, 225, and 250 °C. The polymerization (ring‐opening and crosslinking reactions) of T‐ea, T‐a, and T‐dh bio‐based benzoxazines was investigated by FTIR spectroscopy. Cure analysis was conducted using differential scanning calorimetry and the changes in thermal properties of the T‐ea, T‐a, and T‐dh bio‐based benzoxazine resins and their corresponding thermally crosslinked polybenzoxazines PT‐ea, PT‐a, and PT‐dh were studied by thermogravimetric analyzer. The results indicated that all the thymol‐based polybenzoxazines have shown enhanced thermal stability. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47371.

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