How is water-based polyurethane synthesized?

The entire synthesis process of waterborne polyurethane can be divided into two stages.
The first stage is pre-gradual polymerization, that is, relative molecules are gradually polymerized from oligomer diol, chain extender, water-based monomer, and diisocyanate through solution
A waterborne polyurethane prepolymer with a quality of 1,000;
The second stage is the dispersion of the prepolymer in water after neutralization.
Because of its environmental protection effect, water-based PU has a short history, but it has developed very rapidly. 


Water-based polyurethane includes three types of polyurethane aqueous solution, water dispersion and water emulsion. It is a binary colloidal system. Polyurethane (PU) particles are dispersed in a continuous water phase. It is also called water-based PU or water-based PU.
Due to the diversity of polyurethane raw materials and formulas, many preparation methods and preparation formulas have been studied during the development of water-based polyurethane for about 40 years.


There are many varieties of waterborne polyurethane, which can be classified and differentiated in many ways.
1. In terms of appearance, water-based polyurethane can be divided into polyurethane emulsion, polyurethane dispersion, and polyurethane aqueous solution. The most practical applications are polyurethane emulsions and dispersions, collectively referred to as waterborne polyurethane or polyurethane emulsions. 
2. According to the form of use, water-based polyurethane adhesives can be divided into two types: one-component and two-component according to the form of use. The water-based polyurethane that can be used directly or does not require a cross-linking agent to achieve the required performance is called a one-component water-based polyurethane adhesive. If the required performance cannot be obtained by using it alone, add a crosslinking agent; or the general single-component waterborne polyurethane can be added with a crosslinking agent to improve the bonding performance. In these cases, both the waterborne polyurethane main agent and the crosslinking agent are composed Two-component system. 


According to particle size and appearance, it can be divided into polyurethane aqueous solution (particle size <0.001 micron, transparent appearance), polyurethane water dispersion (particle size: 0.001-0.1 micron, translucent appearance), polyurethane emulsion (particle size: 0.001-0.1 micron, translucent appearance) Diameter>0.1 micron, white turbid appearance);


According to the charge properties of hydrophilic groups, waterborne polyurethanes can be divided into anionic waterborne polyurethanes, cationic waterborne polyurethanes and nonionic waterborne polyurethanes. Among them, the anionic type is more important, and it is divided into two categories: carboxylic acid type and sulfonic acid type.


According to different synthetic monomers, water-based polyurethane can be divided into polyether type, polyester type and polyether and polyester hybrid type. According to the different diisocyanates selected, waterborne polyurethane can be divided into aromatic and aliphatic, or specifically divided into TDI type, HDI type and so on.