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

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 (Td10 of 377 degrees C, Yc 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. A facile and sustainable synthetic strategy has been designed to achieve a series of hydrogen bonding-rich bio-benzoxazine resins possessing a set of properties that are highly desirable in industrial applications.