Bio-based benzoxazine monomers and polymers based on difuran diamine

Benzoxazine monomers with high renewable content made from difuran diamine (DFDA) are presented. The benzoxazine monomers were synthesized by reacting DFDA with several bio-based phenolic compounds and formaldehyde. These systems were purified by precipitation, and depending on composition, the resulting solid powders melt at temperatures ranging between 50 and 150°C to form low viscosity liquids that can be used to impregnate fiber reinforcements. Onset cure temperature varies depending on composition in the range of 150–240°C. The resulting polybenzoxazines have T_g's ranging from 240 to 300°C. It was found that the phenolic structure selected affects curing mechanisms of the DFDA-based benzoxazines, Benzoxazines that have available ortho or para positions on the phenolic structures result in cure without mass loss. It was also found that adding furan rings into the backbone of the polybenzoxazine network provided the added benefit of char yield as high as 60%, as measured by thermalgravimetric analysis temperature ramps in an inert environment to 800°C. Compared with benzene-ring-based benzoxazine counterparts, furan-based benzoxazines showed better thermal stability. In addition to promising processing and thermal characteristics useful for applications requiring high temperature and fire resistance, these materials contain high renewable content.