Process for the preparation of liquid carbodiimide-modified organic polyisocyanates employing organotin catalysts

A process for the preparation of a liquid carbodiimide-modified organic polyisocyanate comprising:

• a. heating an organic polyisocyanate to a temperature greater than 200.degree. C. for a period ranging from 0.5 hour to 5 hours in the presence of a catalytically sufficient amount of an organotin compound selected from the group consisting of a quadrivalent organotin compound described by the following formula:
• ##STR3## wherein Z and Z' are individually alkyl, aryl, alicyclic, heterocyclic, oxyalkyl or acyloxy group having from 1 to 18 carbon atoms and may be the same or different, X is an alkyl, aryl, alicyclic, heterocyclic, oxyalkyl, acyloxy, thioalkyl or thioalkylene acyloxy group having 1 to 18 carbon atoms, Y is equal to X or oxy groups or a group represented by the following formula:
• ##STR4## provided that when Y is this group, X is an alkyl or aryl group, m is equal to 1 except when Y is an oxy group then m is equal to 0, and
• a divalent organotin compound described by the following formula:
• Sn(OOCZ").sub.2
• wherein Z" is alkyl, aryl, alicyclic, heterocyclic having from 1 to 18 carbon atoms,
• b. stopping the reaction by cooling the product resulting from step (a) to a temperature of less than 30.degree. C.