Method for Simultaneous Determination of Partition Coefficients for Cyclic Volatile Methylsiloxanes and Dimethylsilanediol

Cyclic volatile methyl siloxanes (cVMS) such as octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (DS), and dodecamethylcyclohexasiloxane (D6) may enter the environment through industrial activities and the use of various consumer products. Reliable air/water (K-AW), 1-octanol/water (K-OW), and octanol/air partition coefficients (K-OA) for those compounds and their common degradation product, dimethylsilanediol, are critical for accurate prediction of the environmental fate, distribution, and transport of these materials. Challenges have been encountered in determining these properties for cVMS and their degradation products mainly due to the extremely low water solubility of the organosiloxanes, low volatility of their degradation products, and reactivity of those compounds in the water/l-octanol system that can lead to inconsistent and inaccurate partition coefficients. A novel direct method is presented for the simultaneous determination of K-AW, K-OW, and K-OA of organic compounds and was applied to these organosilicon compounds. It was tested in a range of log K-AW values from -6.8 to 3.1, log K-OW values from -0.4 to 8.9, and log K-OA values up to 7. The advantages of the new direct method include the improved accuracy, a shortened measurement time, simultaneous measurement of three partition coefficients of multiple compounds, self-consistency among resultant partition coefficients, and a wide range of applicability including materials that may be slowly reactive in the water/1-octanol system.