Abstract

A systematic study was undertaken of block copolymers of oxyethylene (E) and oxybutylene (B) as structure-directing agents for the preparation of mesoporous silica. Five diblock copolymers (E₄₀B₁₀, E₅₄B₁₁, E₈₉B₁₀, E₅₆B₁₉ and E₅₆B₂₇) and three triblock copolymers (E₂₃B₁₁E₂₃, E₃₁B₁₂E₃₁ and E₄₇B₁₀E₄₇) were synthesized by anionic polymerization. A commercial triblock copolymer (E₄₃B₁₄E₄₃) was also utilized. The phase diagrams for these copolymers in aqueous solution exhibited a cubic phase formed by packing of micelles. Silica was prepared under acid conditions. A simple relationship was demonstrated between the d-spacing from X-ray diffraction of mesostructured silica prepared with the copolymers and a theoretical micelle radius calculated on the basis of the copolymer composition and architecture. Type IV nitrogen adsorption/desorption isotherms were obtained for calcined silica samples, with the step in the isotherm moving to higher p/p^o on increasing B-block length, but the form of the isotherm changing little with E-block length. This may be interpreted in terms of a model of convoluted silica walls penetrating the micelle corona region.