Improved toughening diamine-based polybenzoxazines constructed by controllable curing in polyhexahydrotriazine interpenetrating polymer networks

A series of diamine-based polybenzoxazine (PDMB)/polyhexahydrotriazine (PHT) interpenetrating polymer networks (IPNs) were successfully prepared by sequential polymerization. For the IPN structures, the mechanical and thermal properties were explored. Fourier transform infrared spectrometric studies provide evidence of intermolecular hydrogen bonding (OH…O) between PDMB and PHT, and the compatibility of these two polymers was enhanced by this hydrogen bonding. The homogeneous structures in the PDMB/PHT IPNs with a micro-level phase separation were observed from scanning electron microscope analysis. PDMB, however, is too fragile to form a film. Compared to pure PHT, PDMB/PHT IPNs exhibit 190% higher tensile strength and 284% higher elongation. PDMB/PHT-0.8 reaches an elongation at break of 12.40% and tensile strength of 118.67 MPa, showing better mechanical properties than the other PDMB/PHT IPNs. Results of dynamic thermomechanical analysis indicate a higher heat resistance for PDMB/PHT-0.8, and its glass transition temperature reached 238 °C. © 2022 Society of Chemical Industry.