High Heat-Resistant and Degradable Polybenzoxazines with a Diacetal Structure

Thermosetting resins with high heat resistance are difficult to degrade because of their cross-linking structures. In this work, a kind of diphenol (ACE) with a diacetal strucure is used to synthesize two novel benzoxazine monomers, ACE/aniline-type benzoxazine (ACE-a) and ACE/p-methylaniline-type benzoxazine. Their chemical structures are characterized by Fourier transform infrared (FTIR) spectra and NMR spectra, and the results show that the diacetal structure is successfully introduced. Their curing behaviors and polymerization reactions are studied by differential scanning calorimetry and FTIR spectra. Different cross-linking structures containing the diacetal are proposed for two polybenzoxazines. Their thermal properties are analyzed by dynamic mechanical analysis and thermogravimetric analysis, and the results show that they have excellent heat resistance and thermal stability. For cured ACE-a [P(ACE-a)], its T-g reaches as high as 301 degrees C and the char yield at 800 degrees C under N-2 is 55%. Additionally, these polybenzoxazines can be completely degraded under mild acidic conditions, and the effects on the degradation are investigated systematically. Furthermore, ACE-a is used as a matrix to prepare fiber-reinforced composites with carbon fiber or glass fiber, and then, these fibers can be easily recovered from the composites by degrading the resin.