Syntheses and Characterization of Skeletally Modified Cardanol Based Asymmetric Benzoxazines with Enhanced Thermal and Hydrophobic Properties

Abstract—

Two different skeletally modified cardanol based asymmetric benzoxazines monomers, cardanol-aminophenol/p-toludine and cardanol-aminophenol/4-fluoroaniline, were synthesized using cardanol, 4‑aminophenol, p-toludine/4-fluoroaniline and paraformaldehyde through Mannich condensation reaction. The molecular structure of the benzoxazine monomers was confirmed by FTIR and ¹H-NMR spectral analyses. Cure behavior and thermal stability were studied using differential scanning calorimetry and thermogravimetric analysis respectively. It was found that these benzoxazines exhibit marginally lower polymerization temperature than that of conventional benzoxazines. The formation of polybenzoxazine was confirmed by FTIR analysis after the thermal curing through the cleavage of benzoxazine ring and subsequently led to the formation of three-dimensional cross-linked network structure. Among the polybenzoxazines studied, poly(cardanol-aminophenol/4-fluoroaniline) possess better thermal stability than that of poly(cardanol-aminophenol/p-toludine) due to fluoro substitution in the molecular structure of benzoxazine. Both polybenzoxazines exhibit an excellent thermal and hydrophobic behavior.