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Physical & Chemical properties

Water solubility

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Description of key information

Waived:  The substance is hydrolytically unstable at pH 4, 7, and 9

Key value for chemical safety assessment

Additional information

The MDI/DPG/TPG substance will react with water to form primarily polyurea solids. A low yield of other hydrolysis products, such as 4,4'-methylenedianiline is also possible under highly-mixed conditions. The expected reactivity and low water solubility of such MDI-based prepolymes was demonstrated in an OECD 120 water soluble/extraction study of the MDI-based prepolymer. At loadings of 1 and 10 g/L, under highly mixed conditions, the maximum mean extractable polymer concentrations measured under all pH/temperature conditions was 1.1 ± 0.1 mg/L, or 0.11 ± 0.01% of the total loaded polymer at a pH of 9 (Dow 2006). The percentage of soluble/extractable components did not increase with increased polymer loading, thus indicating that the measured solubility/extractability was influenced by neither the amount of polymer loaded to water nor by the presence of water soluble additives and/or unreacted monomers. The results of this study are similar but less than the estimated water solubility for 4,4'-MDI which is expected. For any polyisocyanate substance, the reaction with an excess of water will always result in complete reaction of all isocyanate functional groups. Any dissolved substance observed is due to fomation of water-soluble reaction products, such as 4,4'-methylenedianiline.

For 4,4'-MDI, the test substance is covered by the category approach of methylenediphenyl diisocyanates (MDI). Hence, data of the category substances can be used to cover this endpoint. Any experimental estimation of water solubility for MDI is questionable and therefore QSAR may be considered. The West et al. (2008) study was an uptodate and valid QSAR method (WSKOWWIN (v1.41) which is part of the Estimation Program Interface (EPI) Suite, v3.20.) to provide a water solubility value of 6.8 mg/L for 4,4'-MDI.