Synthesis, curing behavior and thermal properties of fluorene-containing benzoxazines based on linear and branched butylamines

A series of fluorene-containing benzoxazine monomers based on linear and branched butylamines were successfully synthesized in high purity and good yield through a facile one-pot procedure by the reaction of 9,9-bis-(4-hydroxyphenyl)-fluorene with paraformaldehyde and isomeric butylamines. The chemical structures of the target monomers were characterized by Fourier transform infrared (FT-IR), Elemental analysis, 1H and 13C nuclear magnetic resonance (NMR). The curing behavior of benzoxazine monomers was studied by differential scanning calorimetry (DSC) and FT-IR. The thermal properties of cured polybenzoxazines were measured by DSC and thermogravimetric analysis (TGA). The results reveal that the polarity of solvent and the basicity of butylamines produce clear effects on the synthesis of the butylamine-based benzoxazine monomers. Also, the basicity and steric effect of butylamines exhibit significant effects on the curing behavior of benzoxazine monomers and the thermal properties of their polymers. The glass transition temperature and thermal stability of branched butylamine-based polybenzoxazines are higher than those of the corresponding linear butylamine-based polybenzoxazine and traditional bisphenol A-based polybenzoxazines.