Simultaneous High Strength and Toughness of Lower-Dielectric Epoxysilane-Reinforced Polybenzoxazine via Tuning Network Architectures and Dynamic Heterogeneities

Resolving the inherent strength-toughness trade-off for simultaneous mechanical enhancement remains a long-standing challenge for polybenzoxazine (PBZ) composites in electronic packaging and equipment. Inspired by the hierarchical brick-and-mortar architecture of nacre, an epoxy resin bearing Si–O–Si flexible segments (ES) was incorporated into the cross-linked network of PBZ. The low-density glassy regions derived from the catalytic curing reaction among BZ, ES, and imidazole (IMD) acted as the flexible “mortar”, whereas high-density glassy regions constructed by the thermal curing reaction of PBZI and P(BZ-PESI) served as the rigid “brick”. Herein, the flexural strength, KIC, and impact strength of P(BZ-PESI20) blends with lower-dielectric properties were 114.3%, 304.9%, and 129.0% higher than those of neat PBZI, respectively. It was confirmed that the strengthening and toughening mechanism of the resins originated from the synergistic effects of improved cross-linking density, optimized high- and low-density glassy regions, and induced plastic deformation. These favorable mechanical and lower-dielectric properties were realized by tuning the network architectures and dynamic heterogeneity. This work offers economic and feasible prospects to circumvent the trade-off between strength and toughness and to advance the cross-linked network design of high-performance thermosetting polymers.