Phloretic acid-based multi-benzoxazine monomers: tetramethyl guanidine-triggered synthesis and crosslinking

A. FORCHETTI; MORENO, ADRIÁN; GALIÀ, MARINA; DIANA ESTENOZ; MARISA SPONTÓN; GERARD LLIGADAS

Simposio; 4th International Symposium of Polybenzoxazines; 2021

In this study, we developed an efficient strategy to synthesize biobased di-, tri-, and tetrabenzoxazine compounds using the tetramethyl guanidine (TMG)-triggered esterification reaction of a carboxylic acids with organic halides as a key synthetic step [4]. Briefly, phloretic acid and aniline or furfurylamine were reacted to prepare the corresponding monobenzaxine monomers with a free carboxylic acid moiety. Next, the use of TMG enabled the esterification of these compounds with di-, tri- and tetra-halide aromatic compounds at room temperature to afford a series of multi-benzoxazine monomers tethered to an aromatic core. All monomers were obtained with high purity and yields over 90% and characterized by using Nuclear Magnetic Resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR). The study of all the prepared monomers and resulting thermosets revealed good correlation between the number of oxazine rings in the monomers and the final properties of the crosslinked materials. For example, TGA results demonstrated that the increase the amount of oxazine groups enhances the thermal properties of the synthesized materials. Regarding the furfurylamine-based polybenzoxazines, they presented improved thermal behavior compared to the aniline-based resin, due to the role of furan rings. All materials showed good thermal stability over 300°C in inert and oxidizing atmospheres, and high char yields values. These properties are useful in order to employ these resins in high-performance and flame-resistance applications, due to the high LOI estimated values. We envision that the simplicity and efficiency of this route might be extended not only to prepare benzoxazine monomers with higher functionality but also to incorporate other functional groups in the benzoxazine structure, by taking advantage of the mild conditions required for TMG-promoted esterification reactions.