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Diss Factsheets

Physical & Chemical properties

Water solubility

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water solubility
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is hydrolytically unstable at pH 4, 7 and 9 (half-life less than 12 hours)

Description of key information

Water solubility [3-trimethoxysilylpropyl methacrylate]: not relevant due to rapid hydrolysis


Water solubility [3-(trihydroxysilyl)propyl methacrylate]: the concentration dissolved in water is limited to about 1000 mg/l by condensation reactions, calculated water solubility is 1.0E+06 mg/l at 20°C (QSAR)


Water solubility [methanol]: miscible at 20°C

Key value for chemical safety assessment

Water solubility:
2 200 mg/L
at the temperature of:
20 °C

Additional information

The requirement to conduct a water solubility study for the substance is waived on the basis that the registered substance hydrolyses rapidly in contact with water to form 3-(trihydroxysilyl)propyl methacrylate and methanol.

The water solubility of the parent substance, 3-trimethoxysilylpropyl methacrylate, was determined at 20°C to be 82.6 mg/l after 1 hour and 7.54 mg/l after 2 hours in a preliminary study conducted according to OECD Test Guideline 105 using a simplified flask method. Due to the rapid hydrolysis observed during the study, the main test was not conducted and the result is therefore inconclusive. However, the water solubility of the parent substance was predicted to be 2200 mg/l at 20°C using a validated QSAR estimation method. The predicted result is used for assessment purposes.

The silanol hydrolysis product, [3-(trihydroxysilyl)propyl methacrylate], 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 condensation reactions of silanetriols may be modelled as an equilibrium between monomer, dimer, trimer and tetramer, with the linear tetramer cyclising to the thermodynamically stable cyclic tetramer. At higher loadings, cross-linking reactions may occur. The reactions are reversible unless the cyclic tetramer concentration exceeds its solubility; in this case, the cyclic tetramer forms a separate phase, driving the equilibrium towards the tetramer. At loadings below 500 mg/l, 3-(trihydroxysilyl)propyl methacrylate, 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 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 silanol hydrolysis product is very hydrophilic and hence the calculated solubility is 1E+06 mg/l at 20°C 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 valid for use in environmental exposure modelling and toxicokinetics modelling because it is considered to adequately describe the hydrophilicity of the substance and hence the partitioning behaviour.

Methanol is reported to be miscible in water at 20°C (OECD 2004a).

OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.

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