The latent curing agents are meant for use in a wide range of coatings, adhesives, and sealant applications. They are proved to be very beneficial in conditions that require high build properties. For instance, waterproof coatings and construction sealants. Oxazolidines are used as latent curing agents and can be used in both one and two component PU systems.
In case of one component PU system, these latent curing agents are generally used with aliphatic prepolymers. They enhance fast through-cure with no carbon dioxide gas evolution. On the exposure to moisture, these agents get hydrolysed, yielding reactive amine and hydroxyl functional groups.
The unique properties of these latent curing agents are primarily determined by the curing mechanism, which is entirely different from the conventional “moisture cure” reaction. During this process, moisture reacts directly with the terminal isocyanate of the prepolymer producing gaseous carbon dioxide. It results in blisters and bubbles in the coating film.
Moisture primarily reacts with the oxazolidine rather than with the prepolymer’s terminal isocyanate groups. The underlying process of hydrolysis and ring opening of the oxazolidine generates amine and hydroxyl groups. These amine and hydroxyl groups then subsequently react with the isocyanate of the prepolymer without the evolution of carbon dioxide gas.
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