New selective method for quantification of organosilanol groups in silicone pre-elastomers

The silicone elastomers used for drug delivery are normally reinforced by fumed silica, which contains a high density of silanol groups. These inorganic silanol groups have to be deactivated in order to avoid stiffening the uncured pre-elastomer, also called creep hardening. One commonly used way of achieving this deactivation is to mix the material with low molecular mass organosilanols at an elevated temperature. It is important to be able to quantify the nonbonded organosilanols remaining in the material after manufacture. Traditional testing does not distinguish between inorganic silanols and organosilanols. A new selective method for the quantification of organosilanol groups in silicone pre-elastomers has therefore been developed. This method is based on derivatization of the silanol groups with a mixture of dimethylphenylchlorosilane and tetramethyldiphenylsilazane, so that the silanol groups are replaced with a dimethylphenyl group. The derivatized organosilanols are then determined by liquid chromatography using a size exclusion column and a UV detector. No interference was found from other groups normally present in medical grade pre-elastomers, such as vinyls, hydrides, and inorganic bonded silanol on silica or water. The results agreed well with the nonselective Karl Fischer titration for some short chain silanols.