Nanostructured silica templated by double hydrophilic block copolymers with a comb-like architecture

Abstract

An original way to synthesize nanostructured materials is to use new structuring agents constituted of double hydrophilic block copolymers (DHBC). The originality of these structuring agents is multiple: in water, the hydrosoluble DHBC copolymers can become amphiphilic and form micelles in specific conditions, i.e. after addition of other molecules or after a change of a physicochemical parameter (pH), which selectively makes one of the blocks insoluble in water. The addition of a silica precursor to a micelle suspension can lead to the formation of hybrid mesostructured materials, precursors for mesoporous silica. The micellization process may be reversible and the micelles can then be removed from the silica materials in an aqueous solution at room temperature after application of a dissociation stimulus, leading to the mesoporous materials. A new original DHBC is used here for silica structuring: instead of a classical linear diblock copolymer, it is a diblock copolymer with a linear polyacid block (PAA) and a poly(ethylene oxide) based neutral block (PAMPEO) with a comb-type architecture. It is synthesized by controlled radical polymerization (RAFT method) which permits a control of the block lengths. It is shown here that these new DHBC polymers can form polyion complex micelles by complexation with a natural polyamine and that the micellization is reversible as a function of the pH. It is also shown that the new pH sensitive micelles can act as structuring agents in the preparation of mesoporous silica materials.