Significant Improvement on Polybenzoxazine Toughness Achieved by Amine/Benzoxazine Copolymerization-Induced Phase Separation

Two commercially available amines, octanediamine (ODM) and m -xylylenediamine (MXDM), are chosen for tough polybenzoxazine resin due to their controllable capability to cause phase separation during the copolymerization with benzoxazine monomers. The toughening behavior and phase separation of the cured resins are investigated using tensile tests and analyses of dynamic mechanical analysis (DMA), scanning electron microscope, and thermal gravimetry–gas chromatography/mass spectroscopy. The resulting networks show remarkable toughness without obvious degradation in thermomechanical performance. Especially, when ODM/MXDM molar ratio is 1:1, an elongation rate of 10.55% and a breaking strength of 82.67 Mpa, which are 86% and 128% higher than that of the neat benzoxazine resin, respectively, are achieved. These findings open a new way to improve toughness of brittle polybenzoxazine resins.