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Physical & Chemical properties

Dissociation constant

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Description of key information

The homologous components of this UVCB substance possess ionizable hydroxy groups, whose estimated pKa values range from 14.2 to 15.5 for the lowest- and 14.1 to 14.7 for the highest-molecular weight homologues. These are considere to be irrelevant for the chemical safety assessment (Dow, 2010).

Key value for chemical safety assessment

Additional information

As stated in ECHA guidance of Chapter 7.1 (May 2008), for complex mixtures (e.g. UVCBs) containing ionisable components the assessment of pKa is clearly complicated. Estimation of the individual components’ pKa values, if appropriate, should be considered.The pKa values were estimated using the ACD Labs pKa DB software (v5.12, October 2001). This software is among the accepted estimation methods cited in ECHA guidance Chapter 7.1 (May 2008).The apparent pKa values were estimated for the lowest and highest molecular weight homologues. The homologous components of this UVCB substance possess ionizable hydroxy groups, whose estimated pKa values range from 14.2 to 15.5 for the lowest- and 14.1 to 14.7 for the highest-molecular weight homologues. Although these substances possess terminal hydroyl groups, which are theoretically ionizable, the estimated pKa values of > 14 are considered to be irrelevant for the chemical safety assessment. Comparison of predicted and measured values of pKa for several structurally-related substances indicates that the ACD pKa DB software is accurately predicting pKa values of the amino- and alcohol groups of the NLP polyol substances, typically within ± 0.2 pKa units.