Determining the solubility parameter and the cross-link density of medical grade silicones: Effect of increasing the range of swelling liquids

Four samples of four medical grade silicones were swollen in six “good” liquids (i.e. those with a good swelling ability, in which silicones swell appreciably) at 25°C, until they reached constant mass (i.e. equilibrium). The volume fraction,
φ, of the silicone in the swollen sample was calculated for each grade of silicone. Using a combination of the six φ values obtained in this study and four of those obtained in a previous study, for each silicone grade, φ was plotted against δl, the liquid solubility parameter for the ten liquids used. Using a curve fitting technique a second-order polynomial was plotted through the data points; the minimum in this polynomial provided a value for δp (the polymer solubility parameter). Furthermore, the results showed that the δp values obtained in this study (using ten liquids) were slightly but significantly greater (p < 0.05) than those obtained in a previous study (using four liquids), for grade C6-165 only. Similarly, the χ and υ values obtained in the two studies were only significantly different (p < 0.05) from each other, for grade C6-165.