Sustainable approach towards enhancing thermal stability of bio-based polybenzoxazines

The present work demonstrates a sustainable approach to develop hybrid bio-based polybenzoxazines with thermal performance compatible to the petro-based analogues. Bio-based phenols undergoes Mannich like condensation with 3-aminopropyl triethoxysilane (APTES) and paraformaldehyde in ethanol as reaction medium as well as under solvent-less condition. In comparison to the synthesis in the presence of solvent, the reaction completion time was significantly reduced through solvent-less approach thereby improving the sustainability of procedure. Benzoxazine monomers were structurally characterized using Fourier transform infrared spectroscopy (FT-IR), proton and carbon nuclear magnetic spectroscopy (H-1, C-13 NMR). The synthesised monomers undergo thermally accelerated ring opening polymerization which was evidenced using differential scanning calorimetry (DSC). Silane functionality in monomer is sensitive to moisture and can possibly alter curing profile of resins as well as processing with time. Rheological behavior of the resins after a rest period of 30 days at room temperature was investigated to ensure solvent-less processing. Contact angle measurements on the polybenzoxazine specimen were also performed to interpret the effect of generated siloxane linkages on the hydrophobicity of material. Thermal performance of the hybrid polybenzoxazines has been studied by thermogravimetric analysis (TGA) and results have been compared with the reported petm-based polybenzoxazines.