Development of a new silicon-based transdermal system. I. Study of silicone elastomers and effect of liquid ingredients.

The polarities of four elastomers made of silicon oligomers of different viscosities were investigated by measuring the uptake of swelled solvent in different polarity solvents after 24, 48, and 72 hr of treatment. The solvent uptake provides a good characterization for the polarity of the inside of the matrix. On the basis of the results the oligomers were divided into two groups. The same method has been used for the investigation of the change of the inner polarity of samples containing various amounts of polar and apolar liquid ingredients. It was shown that the polarity of the inside of the matrix is related to the swelling properties. The ingredients used changed the matrix framework, which was also influenced by the type of oligomers. The solvent uptake shows large dependence on the timing of the measurement. Measurements carried out after 48 hr of polymer production showed constant solvent uptakes, indicating that the final structure of the polymer was formed.