In the preparation reaction of polyurethane, acid catalysts are generally rarely used, and acid catalysts (such as benzoyl chloride, inorganic and organic acids) have lower catalysis for the formation reaction of urethane and allophanate role, but it is important that they inhibit the biuret formation reaction and thus inhibit the crosslinking reaction. If there is still a small amount of alkali (KOH for ring-opening polymerization) in the polyether that has not been removed, the alkali metal compound will catalyze the side reaction of crosslinking and gel when reacting with diisocyanate. Therefore, acid can be added to neutralize, and if the acid is slightly excessive, the crosslinking reaction will be inhibited, and the prepolymer can be stored for a long time.
The influence of tertiary amine catalysts on the reaction between isocyanate and hydroxyl compounds, in addition to its basicity, there are also factors such as steric hindrance. Generally speaking, the higher the alkalinity and the lower the steric hindrance, the stronger the catalytic ability. Tertiary amines have a greater impact on the catalytic activity of the reaction between water and isocyanate than that of hydroxyl and isocyanate, so tertiary amine catalysts are generally prepared with dry polyurethane foam. Among all tertiary amine catalysts, triethylenediamine is a catalyst with a special structure. Since it is a heterocyclic compound with no steric hindrance on the N atom of the tertiary amine, it has strong effects on foaming reaction and gel reaction. Its catalytic performance is one of the commonly used catalysts for polyurethane foam, and it can also be used in the preparation of polyurethane adhesives, elastomers, etc. It is estimated that in the water/alcohol mixed system, its catalytic ability to hydroxyl accounts for 80%, and water accounts for 20%. Not only widely used in foam, but also in polyurethane elastomers, adhesives, coatings.
Tag:    tertiary amine catalyst
