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Physical & Chemical properties

Vapour pressure

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vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
according to guideline
other: Effusion method
GLP compliance:
Type of method:
effusion method: Knudsen cell
Specific details on test material used for the study:
Details on test material:
MDI-DPG (MP 102), (mixture), M = 250,6 g/mol, CAS: 88288-99-7, compostion: 4,4’-methylene diphenyl diisocyanate (CAS: 101-68-8) oligomeric reaction products with 2,4’-methylene diphenyl diisocyanate (CAS: 5873-54-1) and oxydipropanol.
28.95 °C
Vapour pressure:
0 hPa

Measured values in detail:

 Temperature (°C)  Pressure (hPa) expeimental  Pressure (hPa) calculated  deviation (%)
28.95  1,74e-05   1,84e-05  -5.60
 28.80  1,64e-05  1,81e-05  -.9.49
42.55   9,99e-05  8,07e-05  23.72
 60.60 4,99e-04   4,76e-04  4.78
 75.50  1,62e-03 1,79e-03   -9.72

Description of key information

All MDI substances have extremely low vapour pressures at room temperature (<0.01 Pa).  Only special laboratories with highest precision could apply the mass-loss Knudsen effusion method for MDI substances at elevated temperatures from 30 to 90°C in order to extrapolate to room temperature. Due to this fact, measurements are difficult to perform and only the most reliable will be taken into account for assessment.


Substances of the ‘Monomeric MDI’ subgroup (4,4’-MDI, 2,4’-MDI, 2,2’-MDI and MDI Mixed Isomers) have the highest vapour pressure, ranging from 0.7 to 8.05 mPa at 20°C. All modified MDI substances of the subgroups ‘Oligomeric MDI’, ‘MDI reaction products with glycols’ and ‘MDI condensation products’ have lower values compared to the basic monomers they are made from.


The overall content of monomeric MDI isomers in all substances and the ratio of 2,4’-MDI and 4,4’-MDI are the main driver of air exposure (shown elsewhere) within the MDI category. The higher molecular weight constituents, i.e. MDI oligomers, condensation adducts, or glycol adducts, all have much higher molecular weight and therefore much lower vapour pressure. These higher molecular weight constituents do not contribute to the overall vapour pressure of the MDI substances. Theoretical vapour pressure calculations support this hypothesis (see Chapter of the Category Justification Document and supporting studies of Sadler 2019 cited there).


In a substance specific study according to the study design of OECD Guideline 104 (Vapour pressure curve) in 2016 using the effusion method in a Knudsen cell the following estimated vapour pressure at 20 °C was extrapolated from the regression equation:

Vapour pressure at 20°C: 0.00065 Pa

Key value for chemical safety assessment

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

Additional information