Synthesis and Characterization of Cardo Bisbenzoxazines and their Thermal Polymerization

Bisbenzoxazines of bisphenol-C (BCO) and phenolphthalein (PHO) were synthesized by condensing 0.05 mol bisphenol-C/phenolphthalein, 0.2 mol formaldehyde, and 0.1 mol aniline. Both BCO and PHO were thermally polymerized via ring-opening polymerization. The resultant cross-linked polymers (PBCO and PPHO) were characterized by solubility, Infrared (IR), Nuclear Magnetic Resonance (NMR), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). The bisoxazines and their polymers followed two-step degradation. Both BCO and PHO undergo selective ring-opening polymerization over the temperature range 100–150°C and are thermally stable up to about 250°C. The % residue at 550°C is substantially higher for PHO samples (56–67%) than BCO samples (20–25%), indicating the highly thermally stable nature of PHO. A ring transformation reaction is also supported by DSC. New thermosetting materials may be useful for specific applications to be exploited.