Question

Give general information about zirconium metal complex as a catalyst in urethane coating reaction, mention the cost, activity, selectivity and sensitivity of it

Answer 1

The reaction of isocyanate and hydroxy compounds to form urethanes is the basis for the production of polyurethanes. Metal compounds (e.g., tin, zinc and bismuth compounds) have been known to catalyze the reaction of isocyanate and hydroxyl groups to form urethane.

But there were many problems with the use of these Catalyst.When they r used for polyurethane coatings process,as they catalyse undesirable side reactions and many other problems.

The testing of zirconium acetylacetonate and zirconium tetra-3-cyanopentanedionate, as catalysts for the isocyanate-hydroxy reactionhas shown that zirconium acetylacetonate is a poor catalyst for the urethane reaction. catalytic efficiency of zirconium acetylacetonate for the isocyanate-hydrox reaction to form urethane is low. The solubility of zirconium acetylacetonate and zirconium tetra-3-cyanopentanedionate in solvents commonly used in the production of coatings is poor. Examples of such solvents include esters ketones, glycolesters.The metal complexes with mixed ligands can be prepared by charging the starting zirconium compound into a solution containing the desired ligand(s) at specified mole ratios. The ligand exchange reaction is facile and can be accomplished by blending the starting zirconium or hafnium compound and the desired ligand as a chelating agent at an ambient or slightly elevated temperature. This blending can be carried out in a solvent such as a polyol, e.g. propylene glycol.In most studies, similar or faster dry times were obtained using zirconium concentrations that were at least one-third the concentration of tin.

Catalyst Selectivity
Acceleration of an isocyanate reaction is a selective process.Generally, most catalysts that promote urethane formation will also accelerate side reactions. The selectivity of a metal catalyst can be related to the metal type, steric hindrance of alkyl groups.This reaction can be detrimental to the quality of a formulated coating. Zirconium samples developed minimal gassing even after 1 week.The lack of gassing in the zirconium vial does not necessarily establish it as a more selective catalyst .This result could also indicate hydrolysis of the zirconium catalyst causing deactivation. Therefore, additional tests were conducted to examine catalyst selectivity.

Catalyst Activity

If we talk about the activity, Zirconium tetraacetylacetonate does not function as an effective curing catalyst. Even though the gel time is shorter than the uncatalyzed process, it is still too long. Further, exposure to atmosphere deactivates zirconium tetraacetylacetonate. However, when one of the ligands in zirconium tetraacetylacetonate is replaced with a diketonate with at least 7 carbons in the backbone, or when zirconium tetraacetylacetonate is in a mixture with a metal complex of the present invention, or when zirconium tetraacetylacetonate in mixed with a diketone with at least 7 carbons in the hydrocarbon backbone, an effective catalyst is obtained.

Sensitivity and Cost

To avoid pigment adsorption or interference from other components which may deactivate the catalyst, it would be an advantage if the catalysts can be pre-blended with the isocyanate component in a two component system. However, a number of urethane catalysts also catalyze the dimerization or trimerization reactions of isocyanate and cannnot be pre-blended with the isocyanate component. A solution of a polyisocyanate with the catalysts of this invention showed good compatibility and stability.

Cost of these Catalyst depent on various factors like it's efficiency, desirable condition and more, Therefore it can vary from situation under which it is used.