Isocyanates are a class of compounds that contain isocyanate groups (-N = C = 0) in their molecular structure. It is classified as monoisocyanates, diisocyanates and polyisocyanates according to number of NCO-containing groups. Monoisocyanates as an important organic synthesis intermediates, can be used for the preparation of carbamates insecticides, fungicides, herbicides; diisocyanates and polyisocyanates are to synthesize a series of excellent properties of polyurethane foam, rubber, Elastic fibers, paints, adhesives and so on.

Isocyanates are poorly water-soluble and typically require organic solvent to dissolve. In recent years, with the increasingly stringent environmental regulations and the enhancement of people's environmental protection awareness, the emission of volatile organic compounds from traditional solvent-borne coatings and adhesives has become more and more restricted. The use of water-dispersible isocyanates is of great importance for the above applications. They are currently mainly used as cross-linking components to prepare high performance aqueous two-component coatings or as additives in aqueous dispersion adhesives.

Water-dispersible isocyanates can be roughly divided into two categories: ionic and non-ionic. Non-ionic isocyanates are mainly modified with polyether. Although polyether-modified isocyanates have gained widespread market acceptance in most applications, they have the disadvantage of requiring high content polyether to show good water dispersibility. In addition, strong shear strength will be enforced to ensure excellent dispersion in water.

In order to overcome the above drawbacks, researchers have made the hydrophilic modification of isocyanates by introducing hydrophilic ionic group, such as carboxyl group, but the storage stability of such products is not very good. In addition, hydroxy sulfonic acid or salt is also used to modify isocyanates, but it leads to a noticeable yellowing of the color of the isocyanate, preventing the use of these products as crosslinking components in high-quality coating systems. Recently, Bayer researchers adopted 3- (cyclohexylamine) propanesulfonic acid (CAPS) and 2- (cyclohexylamino) -ethanesulfonic acid to modify isocyanates. The modified isocyanates can be dispered in water well which not require high shear strength. And tertiary amine neutralized sulfonate-modified isocyanates has good storage stability [1].

Although sulfamic acid-modified isocyanates have the advantage of excellent water dispersibility and good storage stability, Bayer researchers have pointed out that other sulfamic acids with similar structures to CAPS and 2- (cyclohexylamino) -ethanesulfonic acid could not be reacted with isocyanate under more intense reaction conditions. Wanhua Chemical researchers, broke the above technical bias to prepare a number of isocyanates with sulfamic acid modification through technological improvements [2].

In summary, many water-dispersible isocyanate products are available after many years of development. In terms of performance, sulfamic acid-modified products are superior to other modified products.

References:

[1] H. J. Lars, Modified Polyisocyanates, CN1190450C, 2005-02-34

[2] Ji Xushun, mehod of sulfamic acid-modified polyisocyanate preparation and application, CN10448232A, 2015-03-25