Strengthening the mechanical properties of polysulfide adhesives by introducing polyurethane

Polysulfide adhesives are often subjected to breakage or even fracture caused by highly loaded vibrations and large deformations from the wing, limiting their practical use in aircraft fuel tanks. Inserting polyurethanes into liquid polysulfide systems is a viable approach to strengthening their mechanical properties and avoiding nonuniform dispersion of the curing agent. In this contribution, a series of sulfur-containing curing agents were prepared by liquid polysulfide and trimethylolpropane tris(3-mercapto propionate) (TMPMP) to minimize the effect of the polysulfide-urea (-NHCOS-) groups on water resistance. Subsequently, the two-component polysulfide adhesives were successfully synthesized via the prepolymerization method, and their chemical structure, mechanical properties, and solvent resistance were systematically evaluated. As expected, the large introduction of sulfur linkages and -NHCOS- groups provided excellent oil resistance and strong mechanical properties for polysulfide adhesives. Notably, Samples 2-4 exhibited the highest tensile strength of 1.11 ± 0.02 MPa, the greatest shear strength of 1.87 ± 0.04 MPa, and the best hardness of 81 ± 2 Shore A, with 122.0%, 523.3%, and 170.0% improvement over the control, respectively. Furthermore, the oil absorption rate of all samples was less than 3.0%, and their tensile strength remained almost unchanged after 30 days of immersion than before. We believe our paradigm can provide a valuable guideline for designing high-performance polysulfide adhesives.