Phloretic acid: a smart choice to develop low-temperature polymerizable bio-based benzoxazine thermosets

The present work demonstrates the synthesis of new bio-based benzoxazine monomers via Mannich-like condensation of naturally occurring raw materials, for example, phloretic acid (PA) and furfurylamine (fa)/stearylamine (sa). The structure of the benzoxazine monomers has been established using proton nuclear magnetic resonance, carbon nuclear magnetic resonance and Fourier transform infrared spectroscopies. The monomers undergoes thermally activated ring opening polymerization to form polybenzoxazine networks, as revealed by non-isothermal differential scanning calorimetry, and the curing temperature for both was observed to be less than 473 K. Curing parameters of the developed monomers have also been compared with the reported bio-based monomers. The rheological behaviour of PA-fa monomer shows that the monomer has narrow processing window with liquefaction temperature at 426 K and gelation temperature at 437 K. Thermal degradation behaviour of polybenzoxazines was studied using thermogravimetric analysis which reveals that polybenzoxazine based on furfurylamine shows relatively high thermal stability and char yield which is credited to the additional cross-linking sites provided by the furan ring. Graphic abstract