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Physical & Chemical properties

Water solubility

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Description of key information

Water Solubility  [tri(isopropoxy)(vinyl)silane]: 130 mg/l at 20°C (QSAR)

Water Solubility [vinylsilanetriol]: Above approximately 1000 mg/l condensation reactions can occur over time, limiting the concentration dissolved in water. The calculated solubility is 1E+06 mg/l (QSAR)

Water solubility [isopropanol]: 1E+06 mg/L at 25°C

Key value for chemical safety assessment

Water solubility:
130 mg/L
at the temperature of:
20 °C

Additional information

The requirement to conduct a water solubility study for the submission substance is waived on the basis that it hydrolyses rapidly to vinylsilanetriol and isopropanol.

However, the water solubility of the parent substance has been calculated using a validated QSAR estimation method to be 130 mg/l at 20°C.

The silanol hydrolysis product, vinylsilanetriol may undergo condensation reactions in solution to give siloxane dimers, linear and cyclic oligomers and highly cross-linked polymeric particles (sol) that may over time form an insoluble gel and a dynamic equilibrium is established. The overall rate and extent of condensation is dependent on nominal loading, temperature and pH of the system, as well as what else is present in the solution.

The silanetriol undergoes reversible condensation reactions in solution to give siloxane dimers, linear and cyclic oligomers. The reactions are reversible as long as the concentrations are low and all species remain soluble; thus, a dynamic equilibrium is established. At higher concentrations one or more of the oligomers may exceed their solubility limit and form a separate phase, or insoluble cross-linked polymers may form, driving the equilibrium towards the oligomer/polymers. At low loadings of vinylsilanetriol, the soluble monomer is expected to predominate in solution (>99%), with small amounts of dimer and oligomers. Condensation reactions are expected to become important at loadings above about 1000 mg/L (or lower under some circumstances) causing the formation of insoluble polymeric particles (sols) and gels over time.  Further information is given in a supporting report (PFA 2016am) attached in Section 13.

The hydrolysis product, vinylsilanetriol, is very hydrophilic and hence the calculated solubility is 1E+06 mg/l using a QSAR method. This QSAR method for water solubility cannot be validated for silanetriols because the saturation concentration of silanetriols in water is limited by condensation reactions rather than lack of true solubility as discussed above. A prediction of 1E+06 mg/l is indicative but has no practical meaning. The prediction is however considered to be valid because it is considered to adequately describe the hydrophilicity of the substance and hence the partitioning behaviour.

Isopropanol has a reported water solubility of 1E+06 mg/L at 25°C (Riddick et al 1986).

References:

PFA (2016am). Peter Fisk Associates, Silanols and aquatic systems, 404.105.003

Riddick, J., Bunger, W.B., Sakano, T.K. (1986). Organic Solvents: Physical Properties and Method of Purification. 4th Edition, John Wiley & Sons, New York