Oxazolidone-Modified Isocyanurate Foams

Oxazolidone-Modified Isor anurate Foams. The 2-oxazolidone, or 2-oxazolidinone, linkage is considered to be a cyclic urethane linkage, but its thermal stability is much higher than that of a urethane linkage. Kordomenos et al (207) compared the thermal stabilities of urethane, oxazolidone and isocyanurate linkages in terms of activation energy by using model compounds. The results obtained were as follows. 

The reason for the thermal instability of the urethane linkage can be attributed to the existence of labile hydrogen, which results in the dissociation of the linkage as shown below  

A one-shot method for oxazolidone-modified isocyanurate foams was proposed by Hayash et al (129). The process, however, resulted in a high-exotherm reaction which caused thermal degradation of the resulting foams. 

Recently, oxazolidone-urethane-modified isocyanurate foams made by the one-shot process have been reported by Fuzesi et al (128, 209, 210). This process consists of a three-component system. Unmodified oxazolidone foams will be described in the following section. 

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An example of the surface flammability in terms of the Butler chimney test of oxazolidone-modified isocyanurate foams is shown in Figure 40. The effect of equivalent ratio on friabUity is shown in Figure... 

The modification linkages include urethane, amide, imide, carbodiimide and oxazolidone linkages. A urethane-modified isocyanurate foam (trade name Airlite Foam SNB, Nisshinbo, Ind. Inc.) was first applied to the petrochemical industry as a seamless fire-resistant insulant in 1965 (39). 

The oxazolidone linkage is a thermally stable and difunctional linkage that has been used for modifying isocyanurate foams (61, 63). Unmodified oxazolidone foams are expected to have improved properties such as temperature stability, flame retardance, and low friability. An attempt to obtain unmodified polyoxazolidone foams was reported (98). The formulation employed is shown in Table 31. 

As opposed to flexible urethane foams, rigid urethane foams have a highly cross-linked chemical structure and a high percent of closed cells, e.g., over 90%. Rigid urethane foams can be classified as follows unmodified (or pure) rigid urethane foams and modified rigid urethane foams, which include isocyanurate-modified, epoxy-modified, amide-modified and oxazolidone-modified rigid urethane foams. 

These foams include isocyanurate-modified rigid urethane foams, isocyanurate-modified flexible urethane foams, urethane-oxazolidone foams, urethane-based IPN foams, and urethane-based hybrid foams. 

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