Controlled Release of Styrene-Divinylbenzene Copolymer Microcapsules by Phase Transformation of Encapsulated Stearic Acid

Functional microcapsules encapsulating stearic acid were prepared by in situ polymerization of styrene and divinylbenzene. Morphology and release rate were investigated by changing preparation conditions. Total monomer concentration was found to be an important determinant of morphology while being a less dominant factor in average diameter of microcapsule. The sustained release of stearic acid was controlled by pore diffusion through porous microcapsule membrane. The permeability was dependent upon total monomer concentration and average diameter of microcapsule. The permeability coefficient increased with an increase of average diameter of microcapsules and decreased with increasing total monomer concentration. The sustained release rate from microcapsules to ambient solution abruptly changed in the vicinity of melting point of stearic acid. This may indicate that functional microcapsules exhibiting temperature-dependent permeability can be prepared.