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Physical & Chemical properties

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Dimethoxy(methyl)vinylsilane is a liquid at standard temperature and pressure, with a measured melting point of <-100°C, and a measured boiling point of 103.9°C. It has a measured relative density of 0.89 at 20°C, a measured kinematic viscosity of 0.51 mm2/s at 20°C and measured vapour pressure values of approximately 3000 Pa, 5400 Pa, 9200 Pa and 15000 Pa at 20°C, 30°C, 40°C and 50°C, respectively.

The substance is classified as a highly flammable liquid according to Regulation (EC) No 1272/2008 on the basis of a measured flash point of 5°C and a measured boiling point of 103.9°C. It has a measured self-ignition temperature of 240°C, and is not explosive and not oxidising on the basis of chemical structure.

In contact with water dimethoxy(methyl)vinylsilane reacts rapidly (half-life of 18.3 min at pH 7, <<2 min at pH 4, 0.7 min at pH 9 and 25°C) to produce methylvinylsilanediol and methanol according to the following equation:

CH3Si(OCH3)2CH=CH2 + 2H2O → CH3Si(OH)2CH=CH+ 2CH3OH

 

Therefore, requirements for testing of water-based physicochemical properties for the substance are waived on the basis of instability in water. The properties of the hydrolysis product, methylvinylsilanediol, are assessed instead. Methanol is miscible with water, has low log Kow (-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C) (OECD, 2004a: SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18 - 20 October 2004, Methanol, CAS 67-56-1).

 

The saturation concentration of the hydrolysis product, methylvinylsilanediol in water is limited by condensation reactions to approximately 700 mg/l. However, it is very hydrophilic (calculated solubility is 5.0E+05 mg/l using a QSAR method) and has a low log Kow (-0.1, predicted).

The hydrolysis product is not expected to be surface active. It is much less volatile than the parent substance (vapour pressure = 2.1 Pa at 25°C, predicted).