Green Strategy for Preparing Multifunctional Biobased Benzoxazine Resins Derived from Renewable Phenolic Acids

The development of high-performance benzoxazine resins using widely available renewable resources is of significant importance for environmental sustainability and practical industrial applications. Among these resources, biomass-derived phenolic acids represent an important class of natural compounds bearing functional groups, holding great potential for the creation of high-performance polymer materials. However, the inevitable decarboxylation reaction at high temperatures has hindered the processing and application of phenolic acid–based polymers. Although previous studies have shown that introducing amide groups into benzoxazine molecules can effectively inhibit decarboxylation and significantly enhance the overall performance of polybenzoxazine resins, methods for producing high-performance benzoxazine resins using abundant phenolic acid resources have not yet been fully explored. Herein, in strict compliance with the principles of green chemistry, two biobenzoxazine monomers (PHBAA-fa and GAA-fa) rich in amide groups and furan rings were developed using renewable raw materials (gallic acid, p-hydroxybenzoic acid, and furfurylamine) and green solvents (polyethylene glycol, ethanol, and ethyl acetate). Notably, GAA-fa exhibits an extremely low curing temperature (182 °C) due to the catalytic effect of the additional phenolic hydroxyl groups. Benefiting from the extensive hydrogen bonding within the resins, the polybenzoxazine resins derived from both monomers exhibit a variety of excellent properties. In particular, poly(GAA-fa) possesses unexpected hydrophobicity (water contact angle = 111°), outstanding thermal stability ( T g = 288 °C, Y C = 64%), and good flame retardancy (HRC = 13.3 J/g·K). The two multifunctional biobased benzoxazines designed in this study not only offer valuable insights into the extended utilization of natural phenolic acids but also demonstrate potential application value in the development of versatile composite materials.