EVALUATION OF THE EFFECT OF THE CYANOPROPYL RADICAL ON THE INTERACTION OF THE METHYLENE GROUP WITH SILICONE STATIONARY PHASES

Values of the solute-polymer interaction parameter of n-alkanes and polar substances between 90 and 200-degrees-C were obtained on two packed columns (OV-101 and OV-105). Experiments carried out with a capillary column confirmed that with non-polar solute-polymer systems the values of both the specific retention volumes and the thermodynamic parameters derived from them are equivalent to those obtained with packed columns. The results showed that n-alkanes mix better with OV-101 and polar substances are better solvents of OV-105. The differences are small, however. Partial molar enthalpies and free energies of solution and mixing were calculated. The contribution of the methylene group of the n-alkanes to the thermodynamic parameters of solution was evaluated. The effect of cyanopropyl group substitution on the contribution of the methylene group to the partial molar free energy of solution of n-alkanes was found to be roughly linear with the cyanoalkyl group content, decreasing as the polarity of the polymer increases. The solubility parameter of the stationary phase increases only slightly when a 5% substitution of cyanopropyl groups is introduced in the polymer.