Stabilization of polyisocyanates against discoloration

The process for preparing a polyisocyanate resistant to discoloration upon storage which comprises distilling said polyisocyanate in the presence of at least about 25 ppm of an organic phosphite selected from the group consisting of

• 1. triphenyl phosphite,
• 2. diphenylisodecyl phosphite,
• 3. trisononylphenyl phosphite,
• 4. trilauryl phosphite, and
• 5. mixtures thereof;
• and adding to the resultant distillate a stabilizer selected from the group consisting of
• 1. o,o-di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonte,
• 2. tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane,
• 3. bis(2-(4-hydroxy-3,5-di-tert-butylphenyl)ethyl)sulfide,
• 4. octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate, and
• 5. mixtures thereof;
• and
• wherein said stabilizer is employed in quantities of from about 20 ppm to about 250 ppm.

A polyisocyanate containing as a stabilizer against discoloration from about 10 ppm to about 250 ppm of a mixture comprising

• A. an organic phosphite selected from the group consisting of
• 1. triphenyl phosphite,
• 2. diphenylisodecyl phosphite,
• 3. trisnonylphenyl phosphite,
• 4. triisodecyl phosphite,
• 5. trilauryl phosphite, and
• 6. mixtures thereof;
• and
• B. a member of the group consisting of
• 1. o,o-di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate,
• 2. tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane,
• 3. bis(2-(4-hydroxy-3,5-di-tert-butylphenyl)ethyl)sulfide,
• 4. octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate, and
• 5. mixtures thereof;
• and
• wherein the equivalent ratio of B:A is from about 0.01:1 to about 10:1.

A process for preparing a polyisocyanate resistant to discoloration upon storage which comprises distilling said polyisocyanate in the presence of at least about 25 ppm of an organic phosphite and adding to the resultant distillate a stabilizer mixture comprising

• A. an organic phosphite selected from the group consisting of
• 1. triphenyl phosphite,
• 2. diphenylisodecyl phosphite,
• 3. trisnonylphenyl phosphite,
• 4. triisodecyl phosphite,
• 5. trilauryl phosphite, and
• 6. mixtures thereof;
• and
• B. a member of the group consisting of
• 1. o,o-di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate,
• 2. tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane,
• 3. bis(2-(4-hydroxy-3,5-di-tert-butylphenyl)ethyl)sulfide,
• 4. octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate, and
• 5. mixtures thereof;
• and
• wherein the equivalent ratio of (B) :
• (A) is from about 0.01:1 to about 10:1.