Facile and eco-friendly synthesis of hydrogen bonding-rich bio-based bisbenzoxazine resins with low surface free energy, strong adhesion strength and high thermal stability†

Abstract

A facile and eco-friendly synthetic strategy has been developed to achieve a series of hydrogen bonding-rich bio-based thermosetting resins in this study. Using both safe and green solvents, we successfully synthesized target bio-based bisbenzoxazines (DcTa-fa, DcTa-sa, and DcTa-da) with high purity from five different naturally resourced raw materials. The chemical structures of the obtained bisbenzoxazine monomers were verified by nuclear magnetic resonance technology (including ¹H and ¹³C NMR, two-dimensional ¹H–¹H nuclear Overhauser effect spectroscopy (NOESY), and ¹H–¹³C heteronuclear multiple quantum coherence (HMQC)) and Fourier transform infrared spectroscopy (FT-IR). The polymerization processes were systematically investigated by differential scanning calorimetry (DSC) and in situ FT-IR analysis. Contact angle measurements were conducted and the corresponding results revealed tunable surface properties during the polymerization process of each bio-based bisbenzoxazine resin. In order to understand the relationship between the chemical structure and surface properties, more detailed FT-IR analyses were carried out to investigate the hydrogen bonding networks in the resulting polybenzoxazines. Notably, poly(DcTa-fa) presented excellent thermal stability (T_d10 of 377 °C, Y_c of 53.7 wt%) and strong adhesion strength (5.232 ± 0.26 MPa), while poly(DcTa-sa) and poly(DcTa-da) showed outstanding surface properties with very low surface free energy values (22.91 and 22.84 mJ m⁻²). These results highlight the utility of smart and sustainable benzoxazine chemistry and offer a facile and green synthetic approach to access hydrogen bonding-rich bio-based benzoxazine resins with many attractive properties.