Triblock copolymers as templates in mesoporous silica formation:: Structural dependence on polymer chain length and synthesis temperature

Mesoporous silica can be formed with amphiphilic molecules acting as structure-directing templates in dilute systems. The templating properties of five related triblock copolymers, (EO)(x)-(PO)(y)-(EO)(x) (Pluronic L101, P103, P104, P105, and F108), have been investigated regarding the length of the EO blocks as well as the temperature of the synthesis. It was found that the number of EO units is essential in determining which silica mesophase is obtained. Lamellar structure is obtained with short EO chains (4 units); hexagonal structure, with medium length EO chains (17-37 units); and cubic structure, with long EO chains (132 units). The hydrophobicity of the (EO)(x)-(PO)(y)-(EO)(x) polymer is strongly affected by the temperature. This is to some extent reflected in the silica mesostructure formed; a multilamellar vesicle morphology can be obtained at elevated synthesis temperatures. Also, the temperature has an influence on particle size.