Not all nitrogen atoms are equal: contribution of peripheral versus internal amines to the observed reactivity and capture properties of melamine dendrons on SBA-15.

The role of different nitrogen atoms in melamine dendrons tethered to SBA-15 is elucidated. For the nitroaldol (Henry) reaction all nitrogen atoms of the capping group participate in the reaction. For metal binding, uptake correlates with the diamine content indicating interior amines are accessible. Carbon dioxide uptake properties are dictated by the presence of the peripheral amines with little interior contribution. The results show that different nitrogen atoms contribute to different processes including catalysis, metal sequestration, and gas separations.

Polymerization of w/o microemulsions for the preparation of transparent SiO2/PMMA nanocomposites.

Reverse w/o microemulsions composed of methyl methacrylate (MMA) forming the oil phase, nonionic surfactants, and water are used for the synthesis of transparent SiO2/PMMA nanocomposites. An inorganic precursor, tetraethoxysilane (Si(OEt)(4), TEOS), is hydrolyzed in the reverse micelles containing aqueous ammonia. During the hydrolysis of TEOS, polymerization of the continuous MMA phase is initiated using AIBN (azobisisobutyronitrile), and after thermal polymerization at 333 K for 12 h, solid blocks of PMMA are obtained in which nanometer-sized silica particles are trapped in the solid polymer matrix. According to small-angle X-ray and dynamic light scattering experiments, the water droplets in MMA microemulsions are 12 nm (R(W) = 13) in diameter, whereas after polymerization of the microemulsion, the SiO2 particles in the transparent SiO2/PMMA composites are 26 nm in diameter. Transmission electron micrographs demonstrate a low degree of agglomeration in the composites. In comparison with materials generated from micelle-free solutions, the particle size distribution is narrow. The reverse micelle-mediated approach produces composites of high transparency comparable with that of pure PMMA.