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Physical & Chemical properties

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Physico-chemical properties

[3-(trimethoxysilyl)propyl]urea is a liquid at standard temperature and pressure, with a measured melting point of -23 °C and a predicted boiling point of 284 °C. It has a predicted density of 1.04 g/cm³ at 20 °C and a predicted vapour pressure of 2.8E-02 Pa at 25 °C.

The substance is not classified as flammable on the basis of a measured flash point of 110 °C and the high boiling point. It has a measured auto-ignition temperature of 375°C, and is not explosive and not oxidising on the basis of chemical structure.

In contact with water [3-(trihydroxysilyl)propyl]urea is predicted to react (half-life 2.8 hours at RT and pH 7) to produce [3-(trimethoxysilyl)propyl]urea and methanol according to the following equation:

 

(CH3O)3SiCH2CH2CH2NHC(=O)NH2 + 3H2O ¿ (HO)3SiCH2CH2CH2NHC(=O)NH2 + 3CH3(OH)

 

Therefore the properties of the silanol hydrolysis product, [3-(trimethoxysilyl)propyl]urea are assessed instead. The hydrolysis product is very soluble in water, 1.0E+06 mg/l (predicted), with a log Kow of -3.3 (predicted). It is not considered to be surface active. The hydrolysis product is less volatile than the parent substance (vapour pressure = 4.1E-07 Pa at 25 °C).

 

Silanetriols may undergo condensation reactions to give siloxane dimers, oligomers and polymers, according to the scheme:

RSi(OH)3  ¿  RSi(OH)2OSi(OH)2R  ¿  RSi(OH)2O[Si(R)(OH)O]nSi(OH)2R

(where R is an alkyl or aryl side-chain)

A highly cross-linked gel may form. The degree of condensation that will occur may vary with:

- Concentration of the silanol; the greater the initial concentration, the greater the degree of condensation. Significant condensation is not expected at concentrations less than approximately 100 mg/l, but is dependent on specific conditions.

- pH; the condensation reaction may be either acid or base catalysed.

- Temperature.

- Other species present.  

- The nature of the R group

Additional information