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Partition coefficient

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All MDI substances are very hydrophobic as seen from the octanol-water partition coefficient (Log Pow). Measurement of the octanol-water partition coefficient for substances of the ‘Monomeric MDI’ subgroup was at the limit of technical feasibility and determined to be 4.52. Due to a combination of low water solubility and water reactivity calculated values had to be determined for all other MDI substances. Calculated values for the substances of the ‘Monomeric MDI” subgroup were in line with the measured values. 


The calculated values for the other MDI constituents range from 5.2 to 24. As expected, predicted octanol-water partition coefficients increase with increasing molecular weight across the category. It should however, be recognised that due to the high reactivity of the NCO group to both water and octanol, these octanol-water partition coefficient values have no scientific meaning and are only provided to perform the environmental hazard assessment.


The log Pow value were also measured for the Monoureas of 4,4’-MDI which are to a small extent (< 1%) formed during the hydrolysis of 4,4’-MDI with water as an intermediate step to form polyureas. Respective monoureas (both NCO- and amino-ended) were synthesized, and their log Pow properties were investigated.


For the Amino-ended monourea, a log Pow below the CLP-threshold of 4 (i.e. 3.3) (indicating no potential for bioaccumulation) was determined. The NCO-ended form could not be eluted from the 0.5 mg/HPLC column used in an OECD Guideline 117 study. Accordingly, a distinct log Pow value could not be determined for this substance.

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