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Trimethoxy(2,4,4-trimethylpentyl)silane and its hydrolysis product (2,4,4-trimethylpentyl)silanetriol contain no chromophores that would absorb visible or UV radiation, so direct photolysis is not likely to be significant. Indirect photolysis resulting from gas-phase reaction with photochemically-produced hydroxyl radicals may occur.

The SRC AOPWIN program (v1.92) has been used to obtain values of the rate constant kOH for reaction of Trimethoxy(2,4,4-trimethylpentyl)silane and its hydrolysis product (2,4,4-trimethylpentyl)silanetriol with hydroxyl radicals. This prediction method has not been validated to assess applicability to silanes and silanols; therefore, there is uncertainty associated with the calculated values obtained.

The overall half-life in air under default conditions of hydroxyl radical concentration was calculated using the following expressions:

kdegair(d-1) = kOH(cm3/molecule.sec) x OH Concair(molecules/cm3) x 24 x 3600

DT50(d) = ln 2/ kdegair(d-1)

Where:

kdegair= total rate constant for degradation in air

kOH= rate constant for reaction with hydroxyl radicals

OH Concair= concentration of hydroxyl radicals in air = 5 x 105OH molecules/ cm3

DT50= half-life

The results are given in table below:

Table: Results of photodegradation in air calculations

Parameter

Result, Trimethoxy(2,4,4-trimethylpentyl)silane

Result,(2,4,4-trimethylpentyl)silanetriol

kOH(cm3/ molecule.sec)

8.76 x 10-12

16.63 x 10-12

kdegair (d-1)

0.37

0.71

DT50(days)

1.8

0.96