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

The solubility and diffusivity of octamethylcyclotetrasiloxane (D4), d ecamethylcyclopenta-siloxane (D5), and dodecamethylcyclohexasiloxane ( D6) oligomers in poly(dimethylsiloxane) (PDMS) have been measured usin g 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 parame ter values were found to range from -0.15 to 0.15 over the temperature range of these measurements. Diffusion coefficient values were of ord er 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 b etween diffusivity and solute molecular weight was developed at each t emperature. Activation energies for diffusion were found to be 4.4 kca l/mol for D4 and 7.1 kcal/mol for D5 and D6.