Microencapsulation of Active Ingredients Using PDMS as Shell Material

We report an efficient and adaptable method for the microencapsulation of active ingredients by a polydimethylsiloxane (PDMS) shell material. The core–shell microcapsules were obtained by phase separation between the core component and the PDMS shell components after repartitioning of the common solvent THF between the PDMS/core material phase and the water phase. For the shell components, two commercially available functional PDMS polymers containing thiol and vinyl side groups were used. Photo-cross-linking in the presence of 2,2-dimethoxy-2-phenylacetophenone (DMPA) by thiol–ene radical addition was used to form a PDMS-thioether cross-linked shell. Variation of the PDMS component thiol to ene ratio resulted in different functionalities on the microcapsules surface and in the bulk, which was analyzed by attenuated total-reflection infrared spectroscopy (ATR-IR) and high-resolution magic-angle NMR-spectroscopy (HR-MAS NMR). Organically modified silica particles were mixed into the PDMS shell, resulting in better mechanical properties of the shell and control over the shell permeability, as measured on the one hand by tensile testing of representative PDMS bulk samples of identical composition as the actual shell material and on the other hand by leaching experiments of the core compounds, such as a tetrathiol and the UV-absorber octocrylene, followed by UV–vis.