Self emulsified PU is a hydrophilic group introduced into the PU molecular chain. The silane coupling agent disperses the PU molecules in water to form a stable dispersion through the hydrophilicity of the hydrophilic group. The polyamine group reacts with the residual isocyanate to expand the chain. The siloxane group of the silane coupling agent hydrolyzes and polycondensates to make the system cross-linked. The internal cross-linking of the system is realized while the chain is extended, without affecting the dispersion of the prepolymer. The basic properties of the synthesized silicone modified waterborne polyurethane lotion. With the increase of the mass fraction of silane coupling agent, the lotion gradually turns white from almost transparent liquid, and the average particle size of lotion gradually increases. At the same time, the lotion kept good dispersion stability except for the silane coupling agent with 8.9% mass fraction.

TEM photos of the morphology and structure of the latex particles of the modified waterborne polyurethane lotion synthesized under different silane coupling agent mass fractions, with magnification of 100000 times. The latex particles in all lotion are irregular in shape. Without silane coupling agent, the particle size of latex particles is very small (particle size meter measurement result is 47nm), and agglomeration is obvious; When the mass fraction of silane coupling agent is 1.9%, the particle size of latex particles is small (57 nm), and agglomeration also occurs; When the mass fraction of silane coupling agent is 7.6%, the latex particles that are basically spherical increase, and the particle size also increases significantly.

The specific applications of silane coupling agents in the adhesive industry are as follows:
① Silane coupling agent has been widely used as a treatment agent for bonding glass fibers at home and abroad. It can react with the interface to improve the bonding strength. For example, if silane is not used as the treatment agent for neoprene adhesive bonding, the adhesive peel strength is 1.07 kg/cm2; if amino silane is used as the treatment agent, the adhesive peel strength is 8.7 kg/cm2.

② For the bonding between metal and nonmetal in structural adhesive, silane coupling agent can be condensed with metal oxide or another silane alcohol if silane tackifier is used, so as to make silicon atoms closely contact with the surface of the adhesive. For example, adding silane as tackifier in NBR phenolic structural adhesive can significantly improve the bonding strength.

③ Silane coupling agents have special functions in the bonding of rubber and other materials. It can obviously improve the bonding strength between various rubbers and other materials. For example, when glass is bonded to polyurethane rubber, if silane is not used as the treatment agent, the peel strength of the adhesive is 0.224 kg/cm2. If silane is added, the peel strength is 7.26 kg/cm2.

④ Bonding problems that can not be solved by ordinary adhesives can sometimes be solved by silane coupling agents. For example, aluminum and polyethylene, silicone rubber and metal, silicone rubber and plexiglass can be solved satisfactorily by selecting the corresponding silane coupling agent according to the chemical bond theory. For example, polyethylene and aluminum foil can be bonded with vinyl tert butyl peroxide silane (Y-4310); The tensile strength between silicone rubber and metal can reach 21.6 ～ 22.4 kg/cm2 with butadiene triethoxysilane. Common adhesives or resins can not only improve the adhesive strength, but also increase the water resistance and durability of the adhesive force after using coupling agent. For example, polyurethane and epoxy resin have high adhesion to many materials, but the durability and water resistance of adhesion are not ideal; After adding silane coupling agent, the performance in this respect can be significantly improved.