Poly(dimethylsiloxane) coatings for controlled drug release. II. Mechanism of the crosslinking reaction in emulsion

Earlier work focused on the crosslinking of hydroxyl-terminated poly(dimethylsiloxane) (PDMS) particles in a stable latex suitable for spraying onto drug tablets, and established the conditions for eliminating the usual toxic catalysts that would be unacceptable in such pharmaceutical coating materials. Use of these coatings for controlling the rate of release of a drug, however, requires a better understanding of their properties and thus clarification of the mechanism through which the crosslinking occurs. The present study approaches this goal by documenting the effects of anionic, cationic, and nonionic surfactants at various concentrations, and in acidic, neutral, or basic media. FTIR spectroscopy was used to monitor the transportation of crosslinker from the water phase into the hydrophobic PDMS phase. The results suggest a possible mechanism for the crosslinking in sufficient detail to be used to optimize the coatings for drug-release applications. (C) 2003 Wiley Periodicals, Inc.