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

Abstract

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 m 1/2 for neat PBa to 1.49 MPa m 1/2 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.

Mechanically Interlocked Vitrimer Based on Polybenzoxazine and Polyrotaxane

“…Polybenzoxazine (PBz) resins are well known as phenolic-based thermosets with useful characteristics such as near-zero cure shrinkage, low water absorption, good flame retardancy, high thermal stability, and high modulus, which are used for aerospace, electronics, and biomedical applications. − However, the brittleness nature of PBz limits its applications in aerospace and microelectronic fields. Our recent study on using a series of model epoxide-functionalized polyrotaxane (EPR) as reinforcing agents can greatly enhance tensile properties and fracture toughness while maintaining glass transition temperature ( T g ). , However, like traditional thermosetting resins, the end-of-life management of PBz waste is limited to landfill and incineration due to their permanently crosslinked structures. , For thermosets to retain the benefits of a crosslinked structure and recyclability, it is necessary to replace covalent crosslinking with associative or reversible bonds. − The rich molecular variability of the PBz chemical structure offers opportunities to form covalent adaptable networks (CAN) with self-healing, degradability, and recyclability characteristics . Typically, PBz CAN with associative dynamic covalent bonds are also called a PBz “vitrimer” because the viscosity of this network above their dissociation temperature follows the Arrhenius relationship with temperature, similar to vitreous glasses.…”