Polyisocyanate (generally including diisocyanate unless otherwise specified) is one of the essential raw materials for all polyurethane materials, and there are many types of it. In terms of functionality, there are diisocyanates, triisocyanates and polyisocyanates. If classified according to the presence or absence of aromatic rings, there are aromatic isocyanates and aliphatic isocyanates. From the connection between the core group (alkyl group or aryl group) of the organic isocyanate and the isocyanate group, polyisocyanates are divided into aromatic and araliphatic. , pure aliphatic, alicyclic, cycloaliphatic and other types.

Pure aromatic isocyanate raw materials include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (NDI), p-phenylene diisocyanate (PPDI), dimethyldiphenyl diisocyanate (TODI), and more. Methylene polyphenyl isocyanate (PAPI), etc. 1,6-hexamethylene diisocyanate (HDI) and trimethyl-1,6-hexamethylene diisocyanate (TMHDI) are pure aliphatic diisocyanates.

Xylylene diisocyanate (XDI) and tetramethylisoxylylene diisocyanate (m-TMXDI) belong to the araliphatic group.

Isophorone diisocyanate (IPDI), 1,4-cyclohexane diisocyanate (CHDI), dicyclohexylmethane diisocyanate (H12MDI), and methylcyclohexyl diisocyanate (HTDI) belong to alicyclic groups.

Cyclohexane dimethylene diisocyanate (HXDI) and norbornane diisocyanate (NBDI) are cycloaliphatic.

Considering the industrial sources of raw materials, economy and product physical properties, the aromatic polyisocyanate raw materials actually used in the polyurethane industry are currently TDI, MDI and PAPI. Among them, TDI is mainly used to manufacture flexible polyurethane foams, coatings, and castings. Type polyurethane elastomers, adhesives, pavement materials and plastic tracks, etc. MDI is used to manufacture thermoplastic polyurethane elastomers, synthetic leather resins, shoe sole resins, one-component solvent-based adhesives, etc. PAPI is mainly used to synthesize hard Polyurethane foam, adhesives, etc. There are also some aliphatic diisocyanates such as HDI and IPDI used in non-yellowing polyurethane paints. Special aromatic diisocyanates such as NDI are used in high-performance polyurethane elastomers. Triisocyanates are mostly used as cross-linking agents.