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No. 4

No chemistry required (it would not hurt to know some)

 

Some chemistry or physics required


Catalysts  
 
Amine Catalysts  
The amine catalysts used in the preparation of polyurethanes are t-amines with multiple functionality. These amine catalyst are excellent for catalyzing the water reaction in aromatic isocyanate foams. The are commonly called "blowing"  catalysts because they accelerate the water reaction and the formation of carbon dioxide.     PMDETA is an excellent catalyst for the preparation of partially blown rigid foams or moldings. There is large variety of multi-amine functional catalysts available.

Evaporation of amines from foams is one of the factors for fogging of car windows and for "amine odor" of foams. Hydroxyl group containing catalysts can reduce volatility and odor.   This an example of a t-amine catalyst with hydroxyl functionality.

Catalysts which favor the reaction of an isocyanate with a hydroxyl group are called gelling catalysts. For the formation of a good foam a balance between gelation and blowing is required.    

Diethylenetriamine is one of the few amines which give good gelation properties. 

Quaternary ammonium compounds can function as trimerization catalysts   The formate and the 2-ethylexanoate are delayed action trimerization catalysts.

Metal Catalyst  
Organotin compounds, specially dibutyltin dilaurate and stannous octoate are the most often used metal catalysts. Dibutyltin dilaurate is a strong gelation catalyst, selective for hydroxyl reaction over water reaction.  Stannous octoate is the standard tin catalyst for slabstock application.   There is a concern about organotin catalysts in the environment.
Not considered an organotin compound, low in toxicity. This compound is actually the 2-ethylhexanoate.

Some of the potassium salts are excellent trimerization catalysts and are used in the preparation of isocyanurate foams used in flame retardant applications.  

Besides the octoate also the acetate salt acts as a trimerization catalyst
 


Last edited on:

November 20, 2006

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