Studies on nitrile substituted bisphenol-F and bisphenol-Z based benzoxazines with enhanced thermal and hydrophobic properties

Two types of structurally different benzoxazines (BF-abn and BZ-abn) have been developed using bisphenol-F and bisphenol-Z with 4-aminobenzonitrile and paraformaldehyde through Mannich condensation reaction under an appropriate experimental conditions. Molecular structure of benzoxazine was confirmed by FTIR and 1H-NMR spectral analyses. Cure behavior and thermal stability were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) respectively. The results from DSC analysis indicated that these benzoxazines exhibit marginally lower polymerization temperature than that of conventional benzoxazines. Further, the curing behavior of both benzoxazine samples were studied at two different heating rates viz. 10 °C/min and 20 °C/min to ascertain their heat releasing properties. 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. Results from TGA infers that among the benzoxazines studied, poly(BF-abn) possess better thermal stability than that of poly(BZ-abn). Further, the values of LOI calculated using char yield obtained at 850 °C from TGA for poly(BF-abn) and poly(BZ-abn) are 41% and 30% respectively. The values of water contact angle obtained for poly(BF-abn) and poly(BZ-abn) are 138° and 140° respectively. Both benzoxazine samples exhibit an excellent hydrophobic behavior.