Abstract
The porous structure of second- and third-generation polyphenylene-type dendrimers was investigated by adsorption of N2, Ar, and CO2 gases, scanning electron microscopy and small-angle X-ray spectroscopy. Rigid dendrimers in bulk are microporous and demonstrate a molecular sieve effect. When using CO2 as an adsorbate gas, the pore size varies from 0.6 to 0.9 nm. This is most likely due to the distances between dendrimer macromolecules or branches of neighboring dendrimers, whose packing is mostly realized due to intermolecular interactions, in particular, π–π interactions of aromatic fragments. Intermolecular interactions prevent the manifestation of the porosity potential inherent to the molecular 3D structure of third-generation dendrimers, while for the second generation, much higher porosity is observed. The maximum specific surface area for the second-generation dendrimers was 467 m2/g when measured by CO2 adsorption, indicating that shorter branches of these dendrimers do not provide dense packing. This implies that the possible universal method to create porous materials for all kinds of rigid dendrimers is by a placement of bulky substituents in their outer layer.
Highlights
Dendrimers are a unique class of monodisperse macromolecules that differ from other polymers by their well-ordered controllable structure and multifunctional periphery
Rigid-chain dendrimers of polyphenylene type are characterized by microporosity and demonstrate the molecular sieve effect
The use of CO2 as an adsorbate gas that can penetrate into small micropores more effectively at 273 K than N2 and Ar at 77 K allowed us to measure the size of dendrimer micropores in the bulk, which vary in the range from
Summary
Dendrimers are a unique class of monodisperse macromolecules that differ from other polymers by their well-ordered controllable structure and multifunctional periphery. The various structures of dendritic macromolecules as well as the possibility of direct modification of the external dendrimer layer and the internal space of dendrimers determine their numerous possible applications [1,2,3,4,5,6,7,8,9]. The knowledge accumulated to date on dendrimers makes it possible to implement a “from quantity to quality” approach, namely, from expanding the scope of the library of dendritic macromolecules with various chemical structures to the development of new dendrimer-based nanomaterials and discovery of their most promising application areas. Taking into consideration the nanometer sizes of these dendrimers and the presence of internal cavities [14,15,16,17,18], one can assume that dendrimer-based nanomaterials would have a highly developed surface.
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