Polyurethane materials are a general term for a class of macromolecular compounds that have urethane structures in their molecular structure. They are usually prepared by the polyaddition reaction of diisocyanates and polyols.

Polyurethane polymers possess both polar functional groups that allow for physical cross-linking and non-polar and flexible chain segments. When used properly, these polar functional groups can also undergo further chemical cross-linking. These molecular characteristics give polyurethane materials high strength, toughness, and solvent resistance.  

As a high-strength, weather-resistant, and highly adhesive material, polyurethane has been widely used in the coatings field.

Based on the type of isocyanate used to prepare the polyurethane, polyurethane emulsions and corresponding paints can be divided into two main categories: aliphatic and aromatic. Aliphatic paint films have excellent weather resistance and anti-yellowing properties; aromatic water-based polyurethanes are mostly used for interior decorative paints.

According to the size of the particles obtained during polymerization, there are two types: polyurethane emulsions and polyurethane dispersions. Water-based polyurethane dispersions use a unique process to disperse polyurethane particles in water, thus achieving film formation with water as the carrier. Similar to other emulsion film-forming mechanisms, the film-forming effect depends on the ability of the polymer molecules to interpenetrate between the particles.

To increase penetration, on the one hand, the polyurethane molecular chains must be sufficiently flexible and have good fluidity; on the other hand, the emulsion particles should be as small as possible to increase the contact area between the particles and reduce the movement distance of the polymer molecules. Water-based polyurethane dispersions usually have nano-sized particles, appearing translucent or even completely transparent, and are one of the best water-based paint base materials. Water-based polyurethane dispersions are sometimes called nano-emulsions to distinguish them from ordinary emulsions, which have a white appearance.