Grafting Monodisperse Polymer Chains from Concave Surfaces of Ordered Mesoporous Silicas

Surface-initiated atom transfer radical polymerization (ATRP) was used to graft uniform layers of polyacrylonitrile (PAN), poly(2-(dimethylamino)ethyl methacrylate), and polystyrene on concave surfaces of cylindrical mesopores of diameter ∼10 nm and spherical mesopores of diameter ∼15 nm. The grafting process was optimized through the introduction of appropriate amounts of Cu(II) species that act as a deactivator, allowing us to grow polymer layers of controlled thickness (as seen from gas adsorption), which consisted of monodisperse polymer chains of controlled molecular weight (as seen from gel permeation chromatography). For PAN, the degrees of polymerization ranged from DP = 25 to 70, and the polydispersity indexes of the polymer grafted under optimal conditions were as low as M w/M n = 1.06−1.07. Grafted chain densities up to 0.28 chains/nm2 and initiation efficiencies up to 37% were achieved. In cases of spherical mesopores of diameter ∼15 nm, it was possible to introduce significant loadings of polymer (up to 28 wt % in resulting composite) without making the uniform mesopores inaccessible. The specific surface areas of the silica/polymer hybrids were 70−350 m2 g−1, and the thicknesses of the polymer films were controlled in the range up to 1−2 nm without causing any major pore blockage. This work demonstrates new opportunities in the synthesis of well-defined nanostructured/nanoporous silica/polymer hybrids.