Polyurethane Foams Tertiary amine catalysts

Polyurethane formation is mainly accelerated by a tin catalyst, and gas generation, supplied by the water-isocyanate reaction, is mainly promoted by a tertiary amine catalyst. Therefore, if collapsed foams are obtained, increased tin catalyst can solve the foam collapse. Likewise, if... 

Di-n-butyltin catalysts are being used in the preparation of polyurethane foams. Most polyurethane foams utilize aromatic isocyanates such as toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) as the isocyanate, and a polyester or polyether polyols as the coreactant. Tertiary amine catalysts are used to accelerate the reaction with water and formation of the carbon dioxide blowing agent. To achieve a controlled rate of reaction with the polyol, an organotin catalyst can be used. Polyurethane foams are not only applied in place, but are also cast in a factory as slabstocks. These foam slabs are then cut for use in car seats, mattresses, or home furnishings. DBTDL is an excellent catalyst in high resiliency slabstock foams. DBTDL shows an excellent reaction profile for this application replacement for DBTDL in such an end-use is difficult and requires a substantial reformulation of the foam. 

The tertiary amine-catalyzed reactions cause branching and cross-linking and are primarily used for polyurethane foam formation. They are used to accelerate the isocyanate-hydroxyl reaction and give off carbon dioxide. Triethylenediamine is the most prevalent of the tertiary amine catalysts used for polyurethane manufacture. 

There are two major families of catalysts for urethane foams tertiary amines (primary amine react too rapidly with isocyanates to be suitable) and tin catalysts. Both act quite differently during foaming and influence different reactions. They are more likely to be used in combination to achieve the exact balance of reactions needed for a given application and/or the processing method chosen for the job. (See also polyurethane catalysts.)... 

While tertiary amines are adequate catalysts for many reactions, a variety of metal catalysts has been found to be far more powerful. Organotin compounds are now used commercially in many polyurethane processes. The discovery of these catalysts was made independently by Hostettler and Cox [145] and by Britain and Gemeinhardt [146], all of whom were searching for more effective catalysts for foam formation. 

Complexes of organotin with amidines have been found to be excellent catalysts for the preparation of polyurethane foams, which do not have the disadvantage of any amine odor and, in addition, delayed onset of the isocyanate-hydroxyl reaction An example of a mercapto-delayed organotin catalyst is 2,2,4,4-tetrakis(alkyl)- l,3,2,4-dithia-stannetane.55 Amine salts of amino acids, tertiary amino acids, and tertiary amino acid-nitrile compositions, have been found to be effective as delayed action catalysts for polyurethane synthesis. They are particularly effective when used in combination with an organometallic compound, such as an organotin. ... 

Tertiary amines and tin carboxylates are important catalysts in the production of polyurethane foams from polyisocyanates and and polyhydroxy compounds. Many articles have been written on the mechanism of the catalysis of the isocyanate-alcohol reactions by such compounds. Farkas and Mills (1), Entelis and Nesterov (2), Frisch and Rumao (3)and Petrus (4) have written excellent reviews on this subject. Wolf (5) has shown that these catalysts are synergistic to each other. 

The remnant tertiary amines in the polyether polyols obtained in amine catalysis have a negligible effect in the reaction of -NCO groups with hydroxyl groups, in polyurethane fabrication. Generally, the formulations made with these polyols are corrected, by the decrease of the concentration of the amines used as catalysts in the foaming processes, in order to obtain similar reactivities as neutral polyols. 

Polyurethane foams are made by a process in which polymerization and cross-linking is accompanied by gas evolution, which results in the formation of gas bubbles throughout the polymer. The starting materials for polyurethane foam formation are low-molecular-weight polyethers with hydroxyl end groups and an aromatic diisocyanate. Rapid polymerization and gas evolution occurs when the catalyst, typically a tertiary amine, is added ... 

Triethylenediamine (l,4-diazabicyclo-2,2,2-octane, DABCO) n. This tertiary diamine, whose structure is shown below, is the most widely used amine catalyst for polyurethane foams, elastomers, and coatings. It is soluble in water and polyols. 

The formation of isocyanurates in the presence of polyols occurs via intermediate allophanate formation, ie, the urethane group acts as a cocatalyst in the trimerization reaction. By combining cyclotrimerization with polyurethane formation, processibility is improved, and the friability of the derived foams is reduced. The trimerization reaction proceeds best at 90-100°C. These temperatures can be achieved using a heated conveyor or a RIM machine. The key to the formation of PUIR foams is catalysis. Strong bases, such as potassium acetate, potassium 2-ethylhexoate, and tertiary amine combinations, are the most useful trimerization catalyst. A review on the trimerization of isocyanates is available (104). 

Rapid growth of urethane technology can be attributed to the development of catalysts. Catalysts for the isocyanate-alcohol reaction can be nucleophilic (e.g., bases such as tertiary amines, salts and weak acids) or electrophilic (e.g., organometallic compounds). In the traditional applications of polyurethanes (cast elastomers, block foams, etc.) the usual catalysts are trialkylamines, peralkylated aliphatic amines, triethylenediamine or diazobiscyclooctane (known as DABCO), N-alkyl morpholin, tindioctoate, dibutyl-tindioctoate, dibutyltindilaurate etc. 

Control of the reaction sequence in making flexible, open-cell, polyurethane foam using the one-shot process is accomplished by choosing the polyol, the surfactant, and the combination of tertiary-amine and organometallic, usually tin, catalysts. As in the previously described procedures for making urethane elastomers and microcellular products, for foams, polyols— poly(propylene oxide) polyols often containing minor amounts of ethylene oxide—are used. These polyols are selected by functionality, molecular weight, and reactivity (see Table 3). 

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