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

摘要

Polyuretdiones are known as curing agents for hydroxyl-functional polymers. They are typically prepared by dimerising a polyisocyanate to form a uretdione with unreacted isocyanate groups, which can then be extended with a polyol to form a polymeric material containing two or more uretdione groups in the polymer chain. Heating causes the uretdione groups to dissociate giving isocyanates that react with the hydroxyl groups. However, whilst avoiding the need to handle polyisocyanates, they require high temperatures to effect a cure (typically 150°C). It has been found that replacing polyols with polythiols, and using a suitable catalyst, results in an ambient cure composition.