Waterborne PU resin is a new environment-friendly polymer material, which uses water instead of organic solvent as the dispersion medium. Because of its excellent environmental protection, excellent mechanical properties, and good compatibility with other waterborne resins, waterborne PU resins are widely used as adhesives, coatings, and coating products.

Synthesis of waterborne PU resin:
Generally, diisocyanate, oligomer polyol and chain extender are prepolymerized for the synthesis of waterborne PU resin, and the reaction mechanism of this step belongs to gradual polymerization. After the reaction generates a certain molecular weight prepolymer or a high molecular weight PU resin, the phase transfer method is used to emulsify the prepolymer in water to synthesize waterborne PU resin.

Synthetic raw materials of waterborne PU resin:
Polyisocyanates: commonly used varieties include aromatic diisocyanates, including TDI and MDI; Aliphatic diisocyanate HDI and alicyclic diisocyanate IPDI, HMDI, etc. Aromatic PU has good mechanical properties, but its application scope is limited due to the existence of benzene ring, its resistance to yellowing and its high thermal activation temperature. The hydrolysis resistance and storage temperature resistance of aliphatic or alicyclic PU are also better than those of aromatic polyurethane, and they have excellent yellowing resistance. High quality waterborne PU resins are generally synthesized from aliphatic or alicyclic isocyanates.

Macromolecule polyols: The macromolecular polyols used in the synthesis of waterborne PU resin are mainly polyether polyols, polyester polyols, polyethylene glycol, polytetrahydrofuran ether, polyester amide, acrylic acid polyols, etc. Among them, the ether group in polyether polyurethane is easy to rotate, has good flexibility, good low-temperature performance, and the ether group is not easy to hydrolyze, and the water resistance is better than that of polyester polyurethane. However, due to the poor hydrolysis resistance of polyester itself, the storage period of polyester waterborne polyurethane prepared from general raw materials is relatively short.

Chain extenders: small molecule chain extenders include 1,4-butanediol, ethylene glycol, adipic acid alcohol, ethylenediamine, etc. Hydrophilic chain extenders are substances that introduce hydrophilic groups while extending the chain of isocyanate terminated polyurethane prepolymers. They are divided into three types: anionic, cationic and non-ionic. Commonly used are dimethylol propionic acid (DMPA), sodium ethylene diaminoethanesulfonate, diethylenetriamine, methyldiethanolamine, etc. These structures usually contain carboxyl groups, sulfonic groups or secondary amino groups. When the side chains hang onto the polyurethane molecular chains, the PU segments will have functional groups that can be ionized.

Neutralizer: also called salt forming agent, it is a reagent that can react carboxyl group, sulfonic group and other groups to form polymer salt or ionic group. Neutralizers used in anionic waterborne PU mainly include triethylamine, ammonia, sodium hydroxide, etc. Neutralizers used in cationic waterborne PU mainly include acetic acid, CH3I, epichlorohydrin, etc.

Solvent: The commonly used solvent is acetone. Because the viscosity of water-based PU will increase during the reaction, it is difficult to stir and the reaction is not sufficient. Adding acetone to reduce the viscosity is conducive to stirring and the reaction is sufficient. The boiling point of acetone is low. After synthesis, the acetone in waterborne PU can be removed.

IOTA high hardness coating, pls check link, 
https://www.polysilazane.cn/product-inorganic-polysilazane-iota-phps.html