Temperature-Dependent Vapor Pressure of Selected Cyclic and Linear Polydimethylsiloxane Oligomers

Abstract

The isothermal retention times of seven cyclic (D 4 to D 10 ) and nine linear (L 5 to L 13 ) dimethylsiloxane oligomers on a nonpolar gas chromatographic column were determined at temperatures between (308.15 and 438.15) K. Using normal alkanes as standard reference and calibration compounds, these retention times were used to derive liquid state vapor pressures at 298.15 K as well as enthalpies of vaporization that allow for the estimation of vapor pressures over a wide range of temperatures. The data agree within 0.25 log units with vapor pressure values previously reported by Flaningam (1986) but extend those values to lower temperatures and larger oligomers. Cyclic dimethylsiloxanes are more volatile than linear dimethylsiloxanes of a similar size. Oligomers with 10 and more dimethylsiloxane units are expected to sorb appreciably to aerosol at environmentally relevant temperatures.

Evaluation of the three‐phase equilibrium method for measuring temperature dependence of internally consistent partition coefficients (KOW, KOA, and KAW) for volatile methylsiloxanes and trimethylsilanol

“…K AW values for VMS reported in the open literature vary greatly, depending on the methods of determination (Table ). At water solubility limits, K AW values estimated from the saturated vapor pressure and water solubilities are valid. They are smaller than those obtained in dilute solutions in the present study, presumably because of the increased activity coefficients of the VMS as they are diluted in water .…”

Physical properties of secondary photochemical aerosol from OH oxidation of a cyclic siloxane

“…Particles were collected on a carbon film nickel transmission electron microcopy (TEM) grid (SPI 200 mesh) for microscopy and elemental analysis using an RJ Lee Group, Inc. Thermophoretic Personal Sampler (TPS100, RJ Lee Group) (Leith et al, 2014). The TPS100 samples was were collected using hot and cold surface temperatures of 110 and 25 • C, respectively, a flow rate of 0.005 L min −1 , and a 25 min sampling time.…”

Critical Review and Interpretation of Environmental Data for Volatile Methylsiloxanes: Partition Properties

“…1,2 For example, low molar mass cyclic volatile methylsiloxanes (cVMS) such as hexamethylcyclotrisiloxane (D 3 , where D = Si[(CH 3 ) 2 ]O] and octamethylcyclotetrasiloxane (D 4 ) are used as intermediates for synthesis of highmolecular-weight polydimethylsiloxanes (PDMS). As a result, several cVMS including D 3 , D 4 , and their rearrangement products such as decamethylcyclopentasiloxane (D 5 ), dodecamethylcyclohexasiloxane (D 6 ), as well as linear VMS (lVMS) such as hexamethyldisiloxane (L 2 ), octamethyltrisiloxane (L 3 ) and decamethyltetrasiloxane (L 4 ), may be present as impurities in silicone products. In addition, D 5 is a major ingredient in personal care products.…”