Reaction mass of [3-(trimethoxysilyl) propyl]urea, [3-(dimethoxyethoxysilyl) propyl]urea, [3-(methoxydiethoxysilyl) propyl]urea and [3-(triethoxysilyl) propyl]urea.

Endpoint summary

Additional information

Physico-chemical properties

Ureidopropyltrialkoxysilane, mixed methoxy and ethoxy esters is a clear, colourless liquid at standard temperature and pressure. A glass transition at -74°C (major part) and a melting point at -8°C (minor part) were determined. No boiling temperature could be determined; at temperatures >150°C the evaporation of volatile components was observed and the substance decomposes at temperatures > 270°C. The substance has a measured density of 1.13 g/cm3at 20°C, a measured viscosity of 451 mPa.s at 20°C and a measured vapour pressure of 30.3+1.5 Pa at 20°C.

The substance is not classified for flammability on the basis of a measured flash point of 117°C. It has a measured auto-ignition temperature of 356°C, and is not explosive and not oxidising on the basis of chemical structure. On the basis of structure the substance is not expected to be surface active.

In contact with water, the parent substance reacts rapidly to produce the silanol hydrolysis product, [3-(trihydroxysilyl)propyl]urea, methanol and ethanol according to the following equation:

 

H₂NC(=O)NHC₃H₆Si(OCH₃)_x(OCH₂CH₃)_y + 3 H₂O

                                               → H₂NC(=O)NHC₃H₆Si(OH)₃ + x CH₃OH + y CH₃CH₂OH

where x = 0 to 3 and y = 3 - x

 

Therefore, requirements for testing of water-based physicochemical properties for the parent substance are waived on the basis of instability in water. Since the parent substance contains multiple constituents, the water solubility and the partition coefficients of the individual components will be different. The water solubility and Log Kow values of the individual components are shown in Table 1.3.1.

Table 1.3.1 Water solubility and partition coefficients of the individual components

	Water Solubility (mg/l)	Log Kow
[3-(trimethoxysilyl)propyl]urea	2.4E+05	-0.2
[3-(dimethoxyethoxysilyl)propyl]urea	7.4E+04	0.3
[3-(methoxydiethoxysilyl)propyl]urea	2.3E+04	0.8
[3-(triethoxysilyl)propyl]urea	7.0E+03	1.3

 

The properties of the hydrolysis products, methanol, ethanol and the silanol hydrolysis product, are assessed.

Methanol is miscible with water, has a low log Kow(-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C). Ethanol is miscible with water, has a low log Kow(-0.3) and high vapour pressure (7910 Pa at 25°C).

The silanol hydrolysis product is predicted to have water solubility of 1E+06 mg/l at 20°C, a predicted log Kowof -3.3, and a predicted vapour pressure of 4.1E-07 Pa at 25°C. On the basis of structure it is not expected to be surface active. The first dissociation constant of a structurally analogous silanetriol (phenylsilanetriol) has been reported to be around pKa=10.

 

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.