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Physical & Chemical properties

Vapour pressure

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Description of key information

The vapor pressure of MDI/DPG/TPG was 0.00416 Pa at 20C (Dow, 2010).  

Key value for chemical safety assessment

Vapour pressure:
0.004 Pa
at the temperature of:
20 °C

Additional information

The vapor pressure of MDI/DPG/TPG was determined using the effusion method and was 0.00416 Pa at 20 °C (Dow, 2010). Because this substance may contain residues of 4,4'-MDI, the contribution of this potential component should be considered. Four reports are available on determination of vapour pressure for 4,4'-MDI. Pemberton (2001) is the main study and is a Weight of Evidence of a new calculation and the three methods described underneath. The vapour pressure of 4,4'-MDI calculated a best-fit value of 0.00062 Pa at 20°C. Fisk and Langner (1995) followed the EU Method A.4 (modified Watson method). The vapour pressure of 4,4'-MDI was estimated as <0.002 Pa at 20°C, by the modified Watson method, from the boiling point determined in the same study. In the Chakrabarti study (1989) the effusion method (by loss of weight or by trapping vaporisate) was used. Extrapolation from the measured values gave a vapour pressure of 0.0007 Pa at 20°C. In the Brochhagen and Schal study, the EU method A.4 was used, but following a gas saturation (20-70°C). The vapour pressure value is calculated from the experimentally derived vapour concentration over the temperature ranges 20-45°C and 45 -70°C. The vapour pressure was determined to be 0.00049 Pa. The apparent higher vapor pressure of MDI/DPG/TPG is attributed, in part, to the fact that crystaline solids such as 4,4'-MDI have relatively low vapor pressure compared to similar substances in the liquid state.