Synergistic effect of covalent cross-linking and physical hydrogen bonding associations on the mechanical properties of polyurethane thermoset elastomers

Thermoset materials, known for their stable topology structure, have garnered significant interest in recent years for their applications in coatings, foam, adhesives, and other fields. In general, the low chemical crosslinking density of thermoset materials means poor mechanical properties. In this study, we adjusted the topological structure of thermoset elastomers through formula design and controlled their hard segment content at the same level. The mechanical tensile test results show that as the chemical crosslinking density of the elastomer decreases, the fracture tensile strength shows a trend of first increasing and then decreasing. Although the content of amino ester groups in the elastomer is the same, low field nuclear magnetic resonance and Fourier transform infrared analysis show that as the density of the chemical cross-linking network decreases, more physical cross-linking points are formed between the elastomer network chains. Furthermore, the polyurethane hard segment formed an amorphous microphase separation structure in the elastic matrix. This study proves that constructing a moderate physical hydrogen bonding association structure between the network chains in polyurethane cross-linked thermoset elastomers is another important way to prepare thermoset elastomers with excellent mechanical properties.