Polybenzoxazines are a thermosetting polymer that have superior properties to traditional phenolic resins, including near zero volume shrinkage during cure, high glass transition temperature (Tg) and elevated char yields. These enhanced properties make polybenzoxazines exciting candidates for fiber reinforced polymer composites or as the polymer precursor to carbon-carbon composites. However, the grand challenge in the use of polybenzoxazines for these applications is the difficulty in processing for commercial use. Previous work has shown that monofunctional furan-based benzoxazine may offer solutions to these processing challenges without sacrificing performance. However, the single functionality increases the sensitivity to cure from the formation of linear polymers and the inability to crosslink. The difficulty in curing of these monofunctional materials limits their ability to address the grand challenge. A monofunctional furan-based benzoxazine with gastrodigenin as the phenolic derivative was first synthesized by Yu et al. This monofunctional benzoxazine has been reported to undergo crosslinking at temperatures of above 240°C before thermal degradation (380°C). In this report, the ability for the polymer to crosslink was confirmed using thermomechanical analysis and FTIR. The influence that this crosslinking has on carbon formation during pyrolysis was assessed using thermogravimetric analysis paired with both mass spectroscopy (TGA-MS) and infrared spectroscopy (TGA-IR). The carbon structure was analyzed using scanning electron microscopy (SEM), water absorptivity testing for density and porosity, Raman spectroscopy, and X-ray diffraction (XRD). Increases in crosslinking of the polybenzoxazine structure retained char yields of up to 62 % and a carbon bulk density of 1.47 g cm<sup>-3</sup>. This work shows that the monofunctional furan-based benzoxazine with gastrodigenin as the phenolic derivative with its ability to crosslink at high temperatures is an encouraging monomer for applications in high temperature composites.

Formation of a crosslinked network in a monofunctional furan-based benzoxazine and its effect on thermal stability

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