Polyisocyanates
| Isocyanate monomers (selection) |
 Example: diisocyanate. The isocyanate groups are marked in blue , R is a double-bonded organic radical (e.g. a para - phenylene group ). |
 Hexamethylene-1,6-diisocyanate (HDI) |
 Toluene-2,4-diisocyanate (TDI) |
 Diphenylmethane-4,4'-diisocyanate (MDI) |
 Isophorone diisocyanate (IPDI) |
Polyisocyanates are organic compounds that contain two or more isocyanate groups (-N = C = O). They can be divided into aliphatic and aromatic isocyanates . Polyisocyanates are highly reactive compounds. The polyaddition reactions of polyisocyanates with diols (dihydric alcohols ) or polyols (polyhydric alcohols) are the basis of polyurethane chemistry. Alcohols with more than two hydroxyl groups, as crosslinkers, have a significant influence on processing and curing as well as the resulting properties of polyurethane paints and adhesives .
Aliphatic diisocyanates
Aliphatic and cycloaliphatic isocyanates are mainly used in paints due to their light resistance . They are very hard, but tend to react brittle to mechanical loads. The flexibility of the substances can be adjusted by using other amino alcohols . The most important representatives are:
- HDI - H examethylene d i i socyanat
- IPDI - I so p horon d i i socyanat
- CHDI - 1,4 C yclo h exyl d i i diisocyanate
Aromatic diisocyanates
The aromatic polyisocyanates have a higher reactivity towards hydroxyl groups because of the aromatic radical and are therefore preferably used in PU applications. In contrast to aliphatic polymers, they are more flexible. The most important representatives are:
Aromatic polyisocyanates
Due to homologous secondary products of MDA , homologs of MDI also arise in the MDI production process. These "polymeric diphenylmethane isocyanates" (PMDI) are typical secondary constituents of MDI. In contrast to MDI, PMDI has a networking effect.
- PMDI - P olymeres diphenyl m ethan d i i diisocyanate