Toughening mechanism based on the physical entanglement of branched epoxy resin in the non-phase-separated inhomogeneous crosslinking network: An experimental and molecular dynamics simulation study

A type of branched epoxy resin (BEP) with side alkyl chains was prepared by the thiol-ene reaction and used as the copolymerization toughening agent of diglycidyl ether of bisphenol A (ER). The content of BEP on the final properties of the BEP/ER copolymerization toughening system (CPTS) was systematically studied by experimental and molecular dynamics simulation (MDS) data. The results suggest that the BEP/ER CPTS exhibited non-phase-separated inhomogeneous crosslinking network and SEM morphologies can be observed nanoscale aggregate structures, which are formed by the physical entanglement of side alkyl chains in BEP due to the polarity difference between side alkyl chains of BEP and the crosslinking backbone chains. Based on the existence of the additional physical crosslinking points that provided by the physical entanglement of side alkyl chains in BEP, the BEP/ER CPTS can exhibit striking comprehensive mechanical properties. The tensile strength, tensile modulus, elongation at break, and impact strength can be simultaneously improved in the BEP-5 system and reach 101.2 MPa, 2.8 GPa, 4.3%, and 22.5 kJ/m2, respectively. This study not only presents a new toughening strategy through the formation of non-phase-separated inhomogeneous crosslinking network by using facile prepared BEP as the toughening agent, but also provides a theoretical explanation for the generation of physical entanglement in the non-phase-separated inhomogeneous crosslinking network through the MDS data.