Oxazolidone formation

LiBr solubilized by Bu"3PO (or HMPA) was found to catalyze the formation of 2-oxazolidones from organic isocyanates and terminal alkene epoxides. The epoxide substituent appears at the 5-position of the product as shown in equation (122). This outcome is in keeping with rapid trapping by the isocyanate of the halohydrin salt formed by attack of bromide at the primary center. This interpretation requires that oxazolidone formation be faster than epoxide rearrangement data are not available to confirm this point. 

If this mechanism (Reaction 2) is correct the oxazolidone formation... 

As indicated above, the objective of this study was to explore oxazolidone formation expecially as a means of crosslinking epoxy resins. This... 

Kinjo coined the term ISOX to identify resins combining isocyanurate and oxazolidone structures, in which the isocyanurate structure preponderates through using a threefold excess of isocyanate over that required for oxazolidone formation. In consequence of their high degree of isocyanurate cross-linking, such resins may have high T s (ca. 300 C). Pyridines and ter-... 

Tc advance our understanding of oxazolidone systems, three aspects of oxazolidone formation were chosen for study ... 

A number of conclusions may be drawn from the data collected in Tables 4, 5, and 6. Firstly that Peak 1 in the DSC thermogram is attributable to the trimerisation of MDI to form an isocyanurate. This is contrary to the DTA study of oxazolidone formation by Gromakov and coworkers.They reported observing only one peak and attributed it exclusively to the formation of oxazolidone. 

Fourthly, the kinetic parameters derived for the oxazolidone forming reaction (Table 7) are not to be regarded as accurate, owing to difficulties in identifying the baseline between Peaks 1 and 2 precisely. However, the greater heat of oxazolidone formation observed for the EMI catalysed reaction, 141.9 kJmole compared with 44 kJmole when the reaction is catalysed by R NBr, is indicative of a more complete reaction. 

A major feature of the chemistry of the oxazolidone formation reaction, emerging from the of epoxy and isocyanate model compound study, was the competition to that reaction provided by the trimerisation of the isocyanate. This process was a complicating factor in the preparation of linear... 

Table 7. Apparent Kinetic Parameters of Isocyanurate and Oxazolidone Formation Derived by Analysis of DSC Peak Areas... 

Catalyst From Peak 1, Fig. 1 Trimerisation of isocyanate to isocyanurate (IV) From Peak 2, Fig. 1 Oxazolidone formation (I)... 

DSC Study of Oxazolidone Containing Resins. The DSC results of the PGE/ MDI model reaction, using R NBr or EMI as catalyst, showed that both promoted the trimerisation and the oxazolidone formation, with the latter catalyst being more powerful in respect of each reaction. The gained information suggested that by a careful choice of catalyst, catalyst concentration, and... 

The reaction temperature has a measurable influence on the oxazolidone formation when HEXA is used as catalyst, this point is illustrated in Table 12, oxazolidone concentration increasing with temperature increase. 

Second, for the preparation of ISOX resins, the preliminary finding is that EMI, being an effective catalyst for the formation of both oxazolidone and isocyanurate, is the preferred catalyst. This conclusion is based on finding that DABCO is a strong catalyst for isocyanurate formation and HEXA a good catalyst for oxazolidone formation. This latter conclusion is to be regarded as preliminary. 

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