Multihollow polymer microcapsules by water-in-oil-in-water emulsion polymerization: morphological study and entrapment characteristics

Multihollow cross-linked poly(methyl methacrylate) (PMMA) microcapsules were produced by water-in-oil-in-water emulsion polymerization and their applicability to encapsulate water-soluble ingredients was evaluated. In the microscopic analysis, all the PMMA microcapsules showed multihollow structures. In order to evaluate the entrapment efficacy, continuously, a water-soluble ingredient (monosodium phosphate, MSP) was incorporated into the inner voids of the microcapsules, and then its releasing profiles were measured with the storage conditions in pure water. In the releasing test, it was observed that the degree of cross-linking of PMMA had a significant influence on the migration of MSP through the polymer phase. At a sufficient degree of cross-linking of the polymer phase, the leakage of MSP out of the microcapsules was stopped successfully. It is believed that the extremely small network size and the mechanically strong network structure hindered effectively the water flow caused by the concentration gradient between water-soluble ingredients.