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 °C and the char yield at 800 °C under N2 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.

Polybenzoxazine/graphene porous nanocomposites were prepared by sol–gel and subsequent thermal curing. The porous nanocomposites showed low densities ranging from 0.154 to 0.204 g/cm3. The chemical structures and microscopic morphology of the porous nanocomposites were studied using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The electromagnetic wave absorbing ability of the porous nanocomposites was investigated, and the results showed that the minimum reflection loss for the porous nanocomposite with 15 wt% of graphene (PBG‐15) can reach −35.72 dB at a thickness of 2.6 mm with a 1.5 GHz frequency bandwidth. The excellent absorption ability was due to the conductivity loss in the porous nanocomposite. Also, PBG‐15 exhibited good heat resistance with a thermal deformation temperature near 220°C and a char yield of 56%. In addition, the addition of graphene could increase the compressive strength and compressive modulus of the porous nanocomposites by up to 126% and 364%, respectively. These polybenzoxazine/graphene porous nanocomposites have good potential application in light electromagnetic wave absorbing materials.