Synthetic modifications to block-copolymer structure-directing agents lead to polymerizable macromers suitable for templating the growth of mesoporous silica particles, which can subsequently react in situ to form extended nanocomposites and nanocomposite networks. Suitably functionalized triblock polymers can preserve the structure-directing capabilities of the triblock polymer for templating ordered mesoporous silica particle growth and also generate a reactive matrix for subsequent polymer network formation via the reactive end groups. The final self-assembled products are polymer nanocomposites or novel crosslinked nanocomposite networks whose organic/inorganic composition ratios can vary systematically. The novel self-assembly route described here should be generally applicable to the synthesis of intimately mixed nanocomposites and nanocomposite networks, starting from a wide variety of block polymeric template/macromer/ordered silica systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41111.