4-Dimethylaminopyridine Links

The basic nucleophilic poly(iV-alkylacrylamide)-immobilized catalyst 95 was prepared from the active estercopolymer 94 according to the chemistry shown in Eq. 37 [131]. This polymercontained a ca. 8 mol% loading of an analog of ATjAT-dimethylaminopyridine, anucleophilic catalyst that others had immobilized on insoluble cross-linked resins previously. This soluble version was shown to be effective as a catalyst for acylation of hindered alcohols and phenols (Eqs. 38 and 39). This catalyst contained an azo dye as a marker, which facilitated analysis of the phase separation of the polymer-immobilized catalyst. 

Once the rhodium complex was obtained, it was linked through the primary hydroxyl group to the polymeric support. The coupling was carried out by reacting the polymer with 3 equiv of the monomeric Rh complex in the presence of 4 equiv of DCC and 40 mol% of iV,A/ -dimethylaminopyridine (DMAP) at room temperature. 

As mentioned in Section 8.4.3.1., the majority of hydroxy groups in a polyether triol are secondary groups and are comparatively unreactive towards isocyanates. It is therefore necessary to select a catalyst which favours the formation of urethane links relatively more than the formation of gas by the reaction of isocyanate and water. Tin compounds (e.g., stannous octoate and dibutyltin dilaurate) are particularly effective in this respect (cf.. Table 14.3) and are very widely used. In addition to the primary isocyanate-polyol and isocyanate-water reactions, several secondary reactions occur during the preparation of foam. As shown in Section 14.4, the final product may contain allophanate, biuret, isocyanurate and uretidione links. It will be appreciated that in a polymeric system, which is based on a diisocyanate, all of these links (except uretidione) represent points of branching or cross-linking. These secondary reactions are particularly favoured by tertiary amines (e.g., triethylenediamine and 4-dimethylaminopyridine) and these catalysts therefore contribute to the final cross-linking of the foam and hence to the achievement of, for example, a low compression set. Mixtures of tin compounds and tertiary amines are more... 

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