Preparation and characterization of fully renewable polybenzoxazines from monomers containing multi-oxazine rings

Abstract

Two fully renewable benzoxazine monomers containing multi-oxazine rings were synthesized and used to prepare polybenzoxazines. The structures of the monomers, prepared from renewable feedstock (vanillin, guaiacol, octadecylamine and furfurylamine) were supported by FT-IR and NMR spectral analyses. The melting points and curing temperatures were characterized through DSC. Thermal initiated ring-opening polymerization of the monomers was monitored by FT-IR. The solubility of the polybenzoxazines was examined and cross-linking differences between polymers prepared from monomers with mono-oxazine and multi-oxazine rings were clarified. Through energy calculations, substitution was found to preferably take place at the furan ring. The thermal properties were investigated through TGA, which showed good thermal stability (T_d5% at 284 °C and 335 °C) and high char yield (up to 59.6%). The mechanical properties were characterized through DMA, which revealed a glass transition temperature at 155 °C. Due to structure speciality, the polybenzoxazines also showed pH responsiveness and can reversibly change color under different conditions.