Structurally diverse benzoxazines: synthesis, polymerization, and thermal stability

Bisphenol-A is converted to indane bisphenol and spirobiindane bisphenol. The compounds bisphenol-A benzoxazine (BAB), indane bisphenol benzoxazine (IBPB), and spirobiindane bisphenol benzoxazine (SBIB) are prepared by condensing the respective bisphenols with paraformaldehyde and aniline. The structural characterization of the synthesized materials is done by using FTIR, 1H, and 13C NMR. Curing behavior of these benzoxazines and glass transition temperature for polybenzoxazines are studied using differential scanning calorimeter (DSC). The curing exotherm of these benzoxazines is much influenced by the nature of the aromatic unit present in the chosen bisphenol. Compared to the aromatic nucleus in BAB, the indane nucleus present in IBPB shifts the cure exotherm to lower temperatures, whereas the biindane moiety present in SBIB shifts the same to high temperatures. These benzoxazines are thermally cured both at the onset and at the peak maximum of the curing exotherm. The thermal stability of these cured materials is investigated using thermogravimetry. The nature of the aromatic nucleus present in the bisphenol and the temperature at which the curing is done decide the glass transition temperature and thermal stability of the polybenzoxazine.