Method for producing light-coloured polyisocyanates

1. A method for producing light-coloured polyisocyanate mixtures by phosgenation of mixtures comprising MDA and polycyclic aromatic polyamines of formula (II) and/or (III)

and/or higher homologs of the compounds of formula (II) and/or (III), wherein

R denotes hydrogen, an optionally substituted or heteroatom-comprising, saturated or unsaturated alkyl, cycloalkyl, aralkyl or aryl residue and

R1 denotes hydrogen, an optionally substituted or heteroatom-comprising, saturated or unsaturated alkyl, cycloalkyl, aralkyl or aryl residue,

or R and R1 are directly linked to one another so that they form a bicyclic structural element together with the phenylenediamine partial structure, and

R2, R3, R4 and R5 independently of one another denote hydrogen or an optionally substituted or heteroatom-comprising, saturated or unsaturated alkyl, cycloalkyl, aralkyl or aryl residue in ortho, meta or para position to the amino group that is bound to the same aromatic system, and wherein the content of the polycyclic aromatic polyamines (II) and (III) and/or higher homologs thereof in the starting mixtures is 0.001 to 5 wt. %, based on the total weight of MDA, the polycyclic aromatic polyamines (II) and (III) and higher homologs thereof.

2. The method according to claim 1 , wherein R and R1 independently of one another denote hydrogen or methyl and/or the residues R2 to R5 denote hydrogen.

3. The method according to claim 1 , wherein the residue (H 2 N) 2 C 6 HRR1 in formula (II) or (H 2 N) 2 C 6 RR1 in forumula (III) is derived from o-phenylenediamine, 1,2-diamino-3-methylbenzene or 1,2-diamino-4-methylbenzene.

4. The method according to claim 1 , wherein the content of the polycyclic aromatic polyamines (II) and (III) in the starting mixtures is 0.001 to 2 wt. %, based on the total weight of MDA, the polycyclic aromatic polyamines (II) and (III) and higher homologs thereof.

5. Polyisocyanate mixtures obtainable by a method according to claim 1 .

6. Polyisocyanate mixtures comprising MDI and polycyclic aromatic polyisocyanates that are derived from MDA and the polycyclic aromatic polyamines of formulae (II) and (III)

and/or higher homologs thereof, wherein

R denotes hydrogen, an optionally substituted or heteroatom-comprising, saturated or unsaturated alkyl, cycloalkyl, aralkyl or aryl residue and

R1 denotes hydrogen, an optionally substituted or heteroatom-comprising, saturated or unsaturated alkyl, cycloalkyl, aralkyl or aryl residue,

or R and R1 are directly linked to one another so that they form a bicyclic structural element together with the phenylenediamine partial structure, and

R2, R3, R4 and R5 independently of one another denote hydrogen or an optionally substituted or heteroatom-comprising, saturated or unsaturated alkyl, cycloalkyl, aralkyl or aryl residue in ortho, meta or para position, and wherein the content of the polycyclic aromatic polyamines (II) and (III) and/or higher homologs thereof in the starting mixtures is 0.001 to 5 wt.%, based on the total weight of MDA, the polycyclic aromatic polyamines (II) and (III) and higher homologs thereof.

7. The polyisocyanate mixtures according to claim 6 , wherein R and R1 independently of one another denote hydrogen or methyl and/or the residues R2 to R5 denote hydrogen.

8. The polyisocyanate mixtures according to claim 6 , wherein the residue (H 2 N) 2 C 6 HRR1 in formula (II) or (H 2 N) 2 C 6 RR1 in formula (III) is derived from o-phenylenediamine, 1,2-diamino-3-methylbenzene or 1,2-diamino-4-methylbenzene.

9. The polyisocyanate mixtures according to claim 6 , wherein the content of the polycyclic aromatic polyisocyanates that are derived from the said polycyclic aromatic polyamines (II) and (III) in the starting mixtures is 0.001 to 2 wt. %, based on the total weight of MDI and the polycyclic aromatic polyisocyanates that are derived from the polycyclic aromatic polyamines (II) and (III) and higher homologs thereof.

10. A method for the production of polyurethane materials comprising incorporating the polyisocyanate mixtures according to claim 5 .