Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Diphenylsilanediol is a solid at standard temperature and pressure, with a measured melting range of 120.9°C - 172.4°C (394.1 K to 445.6 K) and a predicted density of 1 g/cm3 at 20°C. It has a predicted vapour pressure of 9.9E-06 Pa at 25°C with a predicted log Kow of 2 at 20°C.

It is not expected to be surface active and is not expected to dissociate within the environmentally-relevant range.

There is no indication on the basis of structure and experience in use and handling that the substance is pyrophoric (flammable in contact with air) or flammable in contact with water. The substance is not classified as a flammable solid on the basis of measured flammability of solid study conducted according to EU Test Method A.10. During a preliminary relative self-ignition temperature study, the substance was observed to melt when heated at a temperature of up to 147°C.

The substance may undergo condensation reactions in solution to give siloxane dimers, and linear and cyclic oligomers and highly cross-linked polymeric particles (a colloidal suspension of small solid particles known as 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 silanediols may be modelled as an equilibrium between monomer, dimer, trimer and tetramer, with the linear tetramer cyclising to the thermodynamically stable cyclic tetramer. 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. For diphenylsilanediol, a solution at 25 - 100 mg/l (often the top loading used in ecotox tests) is predicted to contain >99% monomer, with small amounts of dimer, trimer, and cyclic tetramer. At loadings above about 25 - 100 mg/l the concentration of the cyclic tetramer of the silanol hydrolysis product is predicted to exceed its solubility, resulting in formation of a separate phase. In addition, the cyclic tetramer is expected to have a high volatility from water and this may cause losses from water under some conditions. Further information is given in a supporting report (PFA 2013am) attached in Section 13 of the IUCLID dataset.

PFA, 2013am, Peter Fisk Associates, Silanols and aquatic systems, 350.001.003