Achieving very high performance polybenzoxazines from natural renewable isoliquiritigenin: design, preparation and property investigation

Abstract

In this study, we successfully designed and synthesized a series of bio-based benzoxazine resins using p-toluidine/aniline/3-ethynylaniline, paraformaldehyde and natural renewable isoliquiritigenin through a Mannich reaction. Nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, and high-resolution mass spectrometry (HR-MS) were employed to precisely analyze their chemical structures. Besides, the curing behavior of each benzoxazine resin was explored by differential scanning calorimetry (DSC) and in situ FT-IR, which revealed that the synergistic effects from catalytic hydroxyl groups and electron-withdrawing alkynyl groups and carbon–carbon double bonds significantly reduce the curing peak temperatures. Moreover, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) data indicated that the alkynyl groups and carbon–carbon double bonds provide extra cross-linking sites during polymerization, which greatly enhances the thermal stability with a T_d10 of up to 432 °C, T_g of 389 °C, and Y_c of 71.2% at 800 °C. Owing to such outstanding properties, the newly obtained bio-based resins synthesized from isoliquiritigenin are highly suitable for high performance application fields.