SOLUBILITY AND DIFFUSIVITY OF CYCLIC OLIGOMERS IN POLY(DIMETHYLSILOXANE) USING CAPILLARY COLUMN INVERSE GAS-CHROMATOGRAPHY

The solubility and diffusivity of octamethylcyclotetrasiloxane (D4), decamethylcyclopenta-siloxane (D5), and dodecamethylcyclohexasiloxane (D6) oligomers in poly(dimethylsiloxane) (PDMS) have been measured using inverse gas chromatography. Experiments were performed at 150, 175, and 200-degrees-C. Solubility values were used to determine the Flory-Huggins interaction parameter for each species. The interaction parameter values were found to range from -0.15 to 0.15 over the temperature range of these measurements. Diffusion coefficient values were of order 10(-6) cm2/s and were found to be in reasonable agreement with the free volume theory of Vrentas and Duda.1,2 An empirical relationship between diffusivity and solute molecular weight was developed at each temperature. Activation energies for diffusion were found to be 4.4 kcal/mol for D4 and 7.1 kcal/mol for D5 and D6.