Preparation And Properties Of Self-healing Waterborne Polyurethane Based On Disulfide Bonds And Hydrogen Bonds

Water-based polyurethane resins are prepared using water as a solvent and are widely used in coatings,adhesives and leather finishing agents because of their non-polluting and excellent mechanical properties.In order to increase the service life of polyurethane resins,reversible bonds are introduced into the polyurethane molecular chains to make the polyurethane resins self-healing,thus increasing the fields of application.The known self-healing waterborne polyurethane resins heal under either high temperature or being equipped with acidic or alkaline environments.Therefore,the water borne polyurethane resins with self-heal under mild conditions should be urgently designed and prepared.Herein,through the concept of structural design,a series of water borne polyurethane resins with medium and low temperature healing and good mechanical properties were prepared ascribing the incorporation of reversible double sulfur bonds and changing the main chain sequence structure.The main research work includes the following two areas.Self-healable water borne polyurethanes with a synergistic effect of bisulfide bonds and quadruple hydrogen bonds were prepared by regulating the molar ratio of urea-pyrimidinone（UPY）and dimethyl cystine（CDE）in the main chain of water borne polyurethanes.A physical cross-linked network of quadruple hydrogen bonds was constructed by UPY and CDE,which provided the basic mechanical properties and healing ability of the water borne polyurethane resin,while the introduction of covalent bisulfide bonds synergized with non-covalent quadruple hydrogen bonds to make the polyurethane with stronger healing ability and better mechanical properties.The reversibility of the quadruple hydrogen bonding network was confirmed by variable temperature nuclear magnetic（VT-¹H NMR）as well as variable temperature infrared spectroscopy（VT-FT-IR）analysis.When the molar ratio of UPY to CDE was 2:1,the tensile strength of WPU-U₄C₂ was 30.81 MPa and the elongation at break was 313.04%,and the cut specimens could recover 100%of the tensile property index at 60°C for 6 h repair.The low-temperature self-healing waterborne polyurethanes based on disulfide bonds were prepared by introducing 2,2’-diaminodiphenyl disulfide（APDS）and p-menthane-1,8-diol（TMD）monomers.Among them,the aromatic disulfide bonds contained in APDS provided the main contribution to the self-healing polyurethane,while the TMD with asymmetric structure promoted the exchange of disulfide bonds,and the rigid ring contained in TMD further improved the mechanical properties of the polyurethane resin.It was found that the WPU-TMD/APDS system did have better performance than the WPU-BDO/APDS system.the tensile strength of the WPU-TMD/APDS specimen was 27.37 MPa,the elongation at break was 1353%,and the tensile toughness was 136 MJ·m^-3,and the overall performance was more than double that of WPU-BDO/APDS and more than that of WPU-APDS.WPU-TMD/APDS recovered 100%of its tensile properties at 40°C for 1 h.This self-healing recovery was also confirmed by the variation of energy storage modulus values measured by rotational rheometer.