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Home  > Forum  > Special problems & miscellaneous  > Blocking agents for polyisocyanates

Saturday, 22 February 2020

Blocking agents for polyisocyanates

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Friday 11 September 1998 1:00:00 am

I'm looking for blocking agents (high volatility at room temp.) for isocyanate terminated prepolymers. This prepolymers will be water dispersed and allow to cure at room temperature using their isocyanate functionality (once the blocking agent has released the compound).

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Wednesday 07 October 1998 1:00:00 am

Blocking agents are added to water-dispersable binders based on isocyanate to protect the isocyanate group from an unwanted reaction with other components. Isocyanates are capable of reacting with e.g. alcohols or water even at room temperature. These blocking agents are dissociated only during stoving i.e. at temperatures markedly above ambient temperature.
I do not know of any system which dissociates its blocking agent at room temperature. This would not be practical either, since a reaction between the isocyanate and the dispersion medium water would take place.
Frequently used blocking agents are e-caprolactam (in PU powder coatings), butanone oxime or diethyl malonate.

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