The ring-opening reaction of p-cresol-based 1,3-benzoxazine with amine at room temperature was investigated in different solvents. Results show that the reactions proceeded easily in protic solvents, but no reaction occurred in aprotic solvents. For different amines involved in the reactions, both primary and secondary amines can participate in the reaction with benzoxazine, while tertiary amines would hinder the progress of the nucleophilic reaction. The mechanism study demonstrated the feasibility of polymerization of the benzoxazine with amines at room temperature. Moreover, the crosslinking between bifunctional benzoxazine and diamine was realized at room temperature, and the polymer can be obtained.[a] J. Zong, Q. Ran

Lightweight and robust polybenzoxazine foams were prepared using a simple sol–gel method based on a commercially available benzoxazine monomer, BA-a, with hexamethylenediamine as a curing agent and methanol/chloroform as the solvent. By varying the initial concentrations of organic solutions, polybenzoxazine foams with densities of 0.2815 g/cm3 (F-20), 0.4798 g/cm3 (F-30), and 0.6731 g/cm3 (F-40) were prepared. Scanning electron microscopy (SEM) images revealed that all foams possessed open-cell structures, and the morphology of the pore walls can be readily tailored by initial concentrations. As a consequence of the porous structure, the polybenzoxazine foams showed a low dielectric constant (1.47 at 1 MHz for F-20), low dielectric loss (0.003 at 1 MHz for F-20), low thermal conductivity (0.0604 W/(m K) for F-20), and low coefficient of linear expansion value (55.1 ppm/°C for F-20). Moreover, foam F-40 showed a favorable T g of 191.8 °C, char yield of 46.1%, and compressive strength of 71.74 MPa. The outstanding comprehensive performances make the polybenzoxazine foams prepared using this methodology good candidates as lightweight, robust, and thermally stable matrices for many functional applications.