NCO PREPOLYMERS HAVING A LOW CONTENT OF FREE MONOMERIC DIISOCYANATE, AND THE PRODUCTION THEREOF

1 . A process for the production of NCO prepolymers based on toluene diisocyanate having a content of free monomeric toluene diisocyanate of not more than 0.1 wt. % and a viscosity, measured at 50° C., of not more than 5000 mPas, comprising

(1) reacting in a single-step at reaction temperatures of from 40 to 95° C.

(a) one or more polyether polyols having at least 85% secondary OH groups,

with

(b) toluene diisocyanate having a proportion of 2,4-isomer of more than 99.5 wt. %,

wherein the molar ratio of isocyanate groups to hydroxyl groups (or index) in the range of from 1.52:1 to 1.85:1 is maintained, with the proviso that the index does not exceed the value defined by formula (I):

index max =1.5982+7/hydroxyl number of the polyether

2 . An NCO prepolymer based on toluene diisocyanate having a content of free monomeric toluene diisocyanate of not more than 0.1 wt. % and a viscosity, measured at 50° C., of not more than 5000 mPas, comprising the reaction product of:

(a) one or more polyether polyols having at least 85% secondary OH groups, with

(b) toluene diisocyanate having a proportion of 2,4-isomer of more than 99.5 wt. %,

in a single-step reaction at reaction temperatures of from 40 to 95° C., wherein the molar ratio of isocyanate groups to hydroxyl groups (index) is in the range of from 1.52:1 to 1.85:1, with the proviso that the index does not exceed the value defined by formula (I):

index max =1.5982+7/hydroxyl number of the polyether  (I),

3 . A process for the production of polyurethane east elastomer comprising reacting (1) one or more NCO prepolymers of claim 2 , with (2) one or more aromatic amine chain extenders.

4 . The process of claim 3 , wherein (2) said aromatic amine chain extenders are selected from the group consisting of 3,5-diamino-4-chlorobenzoic acid isobutyl ester, 3,5-bis(methylthio)-2,4-diaminotoluene, 4,4′-diamino-2,2′-dichloro-5,5′-diethyldiphenylmethane, 2,4-diamino-3,5-diethyltoluene, isomers of 2,4-diamino-3,5-diethyltoluene and mixtures thereof.

5 . A process for the production of foamed or non-foamed polyurethanes comprising reacting (1) one or more NCO prepolymers of claim 2 , with (2) an isocyanate-reactive component.

6 . A cast elastomer comprising the reaction product of (1) one or more NCO prepolymers of claim 2 , with (2) one or more aromatic amine chain extenders.

7 . A foamed or non-foamed polyurethane comprising the reaction product of (1) one or more NCO prepolymers of claim 2 , with (2) an isocyanate-reactive component.

8 . A moisture-cured film comprising the NCO prepolymers of claim 2 .