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Self-emulsification is an important production method for waterborne polyurethane, which allows the polyurethane molecules to have hydrophilic groups. Therefore, no additional emulsifier or vigorous agitation is required during the emulsification process. This method has the advantage of producing dispersions with small particle size, narrow distribution, and stable storage. Moreover, the mechanical properties and other application performance of the formed film are excellent.

In this process, introducing appropriate hydrophilic groups into the polyurethane molecule structure and well dispersing them in water is crucial for preparing waterborne polyurethane dispersions. Hydrophilic groups can be introduced into the polyurethane molecular structure through raw materials such as polyols or chain extenders during the preparation process. Generally, hydrophilic group-containing chain extenders are used to introduce these groups into the hard segments.

At present, most of the research on anionic waterborne polyurethane dispersions in China focuses on introducing hydrophilic ionic groups into the hard segments through this method. However, this may affect the regularity of the hard segments and reduce their crystallinity. Recently, someone has attempted to synthesize a carboxylic-group-containing polycaprolactone as a soft segment to prepare anionic polyurethane emulsion.

According to the types of hydrophilic groups in the molecular structure, self-emulsifying waterborne polyurethanes can be classified into cationic, anionic, amphoteric, and nonionic types. Cationic polyurethanes are prepared by using V-alkyl diol chain extenders in prepolymer solutions to introduce tertiary amino groups, by quaternization or acid neutralization to achieve self-emulsification. Anionic types use 2,2'-dimethylol propionic acid (DMPA), diamino alkyl iodide, etc. as chain extenders to introduce iodo or carboxyl groups, and then triethylamine or other compounds for neutralization and emulsification. Nonionic types can be obtained by introducing hydroxyl, ether, hydroxymethyl, etc. nonionic groups, especially polyethylene oxide segments, into the polyurethane backbone.

Hydrophilic group introduction methods also include hydrophilic monomer chain extension, polymer reaction grafting, and directly introducing hydrophilic monomers into macromolecular polymer polyols. Among them, hydrophilic monomer chain extension is simple and widely applicable and is currently the main method for preparing waterborne polyurethanes. Directly introducing hydrophilic groups into polyether or polyester polyol molecules is a commonly used method in industrial production abroad and has high application value.