Tetramethyl guanidine-assisted synthesis and thermal crosslinking of multifunctional benzoxazine monomers based on natural phloretic acid

An efficient strategy to synthesize novel biobased multifunctional benzoxazine compounds was developed using the 1,1,3,3-tetramethyl guanidine (TMG)-triggered esterification of natural phloretic acid with organic halides as a key synthetic step. First, phloretic acid was combined with either aniline or furfurylamine to prepare the corresponding carboxylic acid-functional monobenzoxazine monomer. Next, the use of TMG enabled an efficient esterification of these compounds with di-, tri-, and tetra-functional benzyl bromide compounds at room temperature to afford a series of new multi-benzoxazine monomers tethered to an aromatic core. The effect of the functionality of the monomers on the curing process was analyzed, indicating that the reactivity during the thermally induced ring-opening increases with the number of furan and oxazine rings in the monomers. The resulting thermosets revealed good correlation between the number of oxazine rings in the structure of the monomer and the properties of the crosslinked materials. Furfurylamine-based polybenzoxazines showed improved thermal behavior compared to the aniline-based systems, due to the role of furan rings. All materials showed high T-g, good thermal stability, and promising flame retardancy properties.

Automated summary

An efficient strategy was developed to synthesize novel biobased multifunctional benzoxazine compounds by esterifying natural phloretic acid with organic halides using 1,1,3,3-tetramethyl guanidine as a catalyst. The reactivity during the thermally induced ring-opening process increases with the number of furan and oxazine rings in the monomers, and the resulting thermosets showed good correlation between the number of oxazine rings in the monomer structure and the properties of the crosslinked materials. Furfurylamine-based polybenzoxazines exhibited improved thermal behavior compared to aniline-based systems due to the presence of furan rings, with all materials demonstrating high T-g, good thermal stability, and promising flame retardancy properties.