Fracture Behavior of Polybenzoxazine Toughened by Polyrotaxane Molecules and Core–Shell Rubber

The inherent brittleness of polybenzoxazines (PBas) makes them difficult for high-performance microelectronics and composite applications. Conventional toughening approaches are either ineffective or cause a reduction in the glass transition temperature (T g) of PBa. Polyrotaxane (PR), a mechanically interlocked supramolecular polymer, is an effective toughening agent to improve the tensile strength and fracture toughness of various polymers due to its unique topological structure. In this study, the effect of the molecular weight and functional groups of PRs on the morphology and mechanical properties of PR-modified PBa was investigated. PBa toughened by well-dispersed epoxide-functionalized PR (EPR) and benzoxazine-functionalized core–shell rubber (BCSR) was found to greatly enhance fracture toughness without compromising Young’s modulus or T g. The fracture toughness is significantly improved from 0.82 MPa m1/2 for neat PBa to 1.49 MPa m1/2 for PBa/EPR/BCSR. The synergistic toughening effect is explained by the molecularly dispersed EPR in the PBa network, which results in higher network chain mobility, which promotes more cavitation of BCSR and triggers larger matrix plastic deformation. It is believed that the knowledge gained from the present study can help develop tougher polymers for vast engineering applications, especially in electronics, automotive, and aerospace applications.