Curable compositions based on polyuretidiones, polythiols and photoactivable bases and generation of isocyanates from uretidiones

Abstract

Curable compositions based on polyuretidiones, polythiols and photoactivable bases are disclosed. Also a process for generating isocyanate groups by exposing uretidiones to radiation in the range of 100-315 nm is disclosed. The process can be used in a dual curing system for curing compositions that comprise groups that under go photoinduced polymerizations and active hydrogen groups that react with the generated isocyanates.

What is claimed: 
     
         1 . A process for generating isocyanate groups comprising exposing a material containing at least one uretidione group to ultraviolet radiation in the range of 100-315 nm. 
     
     
         2 . The process of  claim 1  in which the uretidione is a polyuretidione containing from 2 to 10 uretidione groups. 
     
     
         3 . The process of  claim 2  in which the polyuretidione is obtained by reacting an isocyanate functional uretidione with a polyol and optionally a blocking agent for isocyanate. 
     
     
         4 . The process of  claim 3  in which the isocyanate functional uretidione is derived from a (cyclo)aliphatic polyisocyanate. 
     
     
         5 . The process of  claim 4  in which the (cyclo)aliphatic polyisocyanate has an isocyanate functionality of 2. 
     
     
         6 . The process of  claim 1  in which the (cyclo)aliphatic polyisocyanate is selected from isophorone diisocyanate and 1,6-hexamethylene diisocyanate. 
     
     
         7 . A process for curing a composition by a plurality of curing mechanisms comprising:
 a providing a composition comprising groups
 i that undergo photoinduced free radical polymerization or photoinduced cationic polymerization, 
 ii at least one uretidione group, and 
 iii at least one active hydrogen group; 
   b exposing the composition to ultraviolet radiation in the range of 100-315 nm so as to polymerize the groups of (i) and generating isocyanate groups from the uretidione group, which react with the active hydrogen groups, the exposure resulting in a cured composition.   
     
     
         8 . The process of  claim 7  in which the groups of (i), (ii), and (iii) are present in one package. 
     
     
         9 . The process of  claim 7  in which the groups of (i), (ii), and (iii) are present in two or three packages.