Kim D.,National Creative Research Initiative Center for Smart Supramolecules |
Kim E.,National Creative Research Initiative Center for Smart Supramolecules |
Lee J.,National Creative Research Initiative Center for Smart Supramolecules |
Hong S.,National Creative Research Initiative Center for Smart Supramolecules |
And 4 more authors.
Journal of the American Chemical Society | Year: 2010
A detailed study of the direct synthesis of polymer nanocapsules, which does not require any template, and core removal, is presented. Thiol-ene click reaction between a CB derivative (1) with 12 allyloxy groups at the periphery and dithiols directly produced polymer nanocapsules with a highly stable structure and relatively narrow size distribution. Based on a number of observations including the intermediates detected by DLS, TEM, and SEM studies, a mechanism of the nanocapsule formation was proposed, which includes 2D oligomeric patches turning into a hollow sphere. A theoretical study supports that the formation of a hollow sphere from a disk-shaped intermediate can be thermodynamically favorable under certain conditions. In particular, the effects of various factors such as monomer concentration, reaction temperature, and medium on the formation of polymer nanocapsules have been investigated, which qualitatively agree with those predicted by our theoretical model. An interesting feature of the polymer nanocapsules was that the polymer shell made of a CB derivative allows facile tailoring of its surface properties in a noncovalent and modular manner by virtue of the unique recognition properties of the accessible molecular cavities exposed on the surface. Furthermore, this approach appears to be applicable to any building unit with a flat core and multiple polymerizable groups at the periphery which can direct polymer growth in lateral directions. Other reactions, such as amide bond formation, can be used for the synthesis of polymer nanocapsules in this approach. This novel approach to polymer nanocapsules represents a rare example of self-assembly of molecular components into nanometer-scale objects with interesting structures, shapes, and morphology through irreversible covalent bond formation. © 2010 American Chemical Society.
Kim H.,National Creative Research Initiative Center for Smart Supramolecules |
Das S.,National Creative Research Initiative Center for Smart Supramolecules |
Kim M.G.,Pohang University of Science and Technology |
Dybtsev D.N.,San |
And 2 more authors.
Inorganic Chemistry | Year: 2011
For the first time, phase-pure interpenetrated MOF-5 (1) has been synthesized and its gas sorption properties have been investigated. The phase purity of the material was confirmed by both singlecrystal and powder X-ray diffraction studies and TGA analysis. A systematic study revealed that controlling the pH of the reaction medium is critical to the synthesis of phase-pure 1, and the optimum apparent pH (pH*) for the formation of 1 is 4.0-4.5. At higher or lower pH*, [Zn 2(BDC) 2(DMF) 2] (2) or [Zn 5(OH) 4(BDC) 3] (3), respectively, was predominantly formed. The pore size distribution obtained from Ar sorption experiments at 87 K showed only one peak, at ̃6.7 Å, which is consistent with the average pore size of 1 revealed by single crystal X-ray crystallography. Compared to MOF-5, 1 exhibited higher stability toward heat and moisture. Although its surface area is much smaller than that of MOF-5 due to interpenetration, 1 showed a significantly higher hydrogen capacity (both gravimetric and volumetric) than MOF-5 at 77 K and 1 atm, presumably because of its higher enthalpy of adsorption, which may correlate with its higher volumetric hydrogen uptake compared to MOF-5 at room temperature, up to 100 bar. However, at high pressures and 77 K, where the saturated H 2 uptakemostly depends on the surface area of a porous material, the total hydrogen uptake of 1 is notably lower than that of MOF-5. © 2011 American Chemical Society.