Epoxidized silicone modified polybenzoxazine resins with synergistic enhanced strength and toughness via tuning cross-linked bonding modes and network topologies

Mechanical properties of thermosetting polymers are intricately linked to the heterogeneity of cross-linked network structures, particularly in balancing strength and toughness. To tackle this trade-off, this work presents how the cross-linking and heterogeneous network influence the viscoelastic and mechanical behaviors of polybenzoxazine (PBZ) resins via tuning cross-linked bonding modes and network topologies. A novel epoxy resin bearing Si-O-Si flexible groups (ES) with different pre-polymerization conversions was incorporated into PBZ cross-linking network. Utilizing imidazole as both a catalyst and curing agent, three network topologies of P(BZ-PESI X ) blends were fabricated via the specific curing cycles. Note that the ratio of thermal and catalytic curing units for three network topologies increased and then dropped as the PESI conversions increased from PESI 0 to PESI 100 . It was found that the chemical reactions involving functional groups, active sites and end groups from free, dangling, and unequal length chains can be significantly enhanced by thermal curing at high temperature ranges. This resulted in a decrease in heterogeneity of the cross-linked network. For cross-linked copolymer networks topology (P(BZ-PESI 40 )), the flexural strength, impact strength and K IC were 26.6 %, 36.7 % and 193.5 % higher than that of neat PBZI respectively. Meanwhile, a significant increase in cross-linking density and storage modulus was observed. It was confirmed that the strengthening and toughening mechanism of resins can be summarized as the synergistic effect of reduced network heterogeneity, plastic deformation effect of Si-O-Si flexible chain segments, and weakened hydrogen-bonding interactions. These insights offer practical and economic prospects for the development of versatile, high-performance thermosetting materials.