Catalysis of Organic..

382 Polyurethane from Natural Oilfrom the final product. Stannous 2-ethylhexanoate is easily hydrolyzed with water,yielding an oxide that is inactive for both transesterifaction and urethane reactions(8). Although carbonate is less expensive and is a better catalyst for this reactionthan the tin catalyst, the necessity of removing the residual salts from the productmakes the carbonate process less attractive overall.Polyurethane FoamThe polyurethane reaction that creates the foam is actually a balance of two separatereactions: blowing and gelling (Figure 6) (9). The blowing reaction takes placewhen water reacts with the isocyanate forming isocyanuric acid, which immediatelydecomposes to the amine and CO 2 . The generation of CO 2 creates bubbles whichcontinue to grow as more CO 2 is formed. Simultaneously, the gelling reaction isproducing the polymer network that constitutes the foam cells and struts. In thisreaction, the polyol or amine from the blowing reaction reacts with isocyanate tocreate a urethane or urea bond respectively.H OH O+ CR'NHOHNR'Blowing ReactionOR'NH 2+OC OHOO NOH CR +R'RNR'OGelling ReactionsH HR'NH O2N NC+R'R'NR'OFigure 6. Polyurethane blowing and gelling reactionsThe literature in this area is quite extensive, and summarizing it is beyond thescope of this discussion, however it must be pointed out that producing a usable