Monodisperse spherical hollow nanoparticles of mesoporous silica featuring mesopores with a radial orientation in the silica shell were synthesized via a dual-templating method. Specifically designed polystyrene latexes with anionic or cationic surface charges acted as the core templates, while cetyltrimethylammonium bromide served as a co-template to structure the mesopore formation during tetraethoxysilane hydrolysis/condensation. The particles were well-separated and presented homogeneous mesoporous silica shells. Average particle diameters were less than 200 nm, and the particles displayed high values of specific surface area and pore volume. The shell thickness and the hollow core diameter could be tuned independently while the radial pore structure was preserved. A detailed analysis of the nitrogen adsorption-desorption isotherms proved that the central cavity was completely isolated from the external medium, that is, only accessible through the radial mesopores of the shell. Consequently, our particles gather the advantages of a well-defined structure, straight penetrating channels across the silica shell, and a high accessible porous volume of the central core. These properties make them far better candidates than simple mesoporous particles for any storage and/or controlled release applications.

Hybrid materials were synthesized by grafting polymer chains from the surface of ordered mesoporous silica (OMS) particles via surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate or styrene. Various types of OMS particles were used as substrates: micrometric particles with ill-defined shape and varying mesopore diameters (9-14 nm), submicrometric polydisperse spherical OMS particles, and monodisperse core-shell particles composed of a dense silica core and an OMS shell, the latter two materials exhibiting ordered mesopores (diameter 2.5 nm) with radial orientation. This work proposes a systematic investigation of the molar mass, molar mass distribution and chain-end structure of both the grafted chains grown from the silica surface and the free chains produced in solution from an additional free initiator. The polymerizations of methyl methacrylate and styrene were perfectly controlled in the homogeneous medium via the ATRP mechanism whereas the study of the grafted chains highlighted the formation of a large fraction of dead species together with the expected population of living chains. The influence of the polymerization conditions and of the OMS particle structure on the occurrence of the extensive termination reactions was studied and discussed.