Research Activities of Sottmann Group

Nanoporous Polymers with Adjustable Pore Size

Synthesis and characterization of nanoporous polymers for heterogeneous catalytic applications

Overview

Nanoporous materials are potential candidates for a wide range of applications. For example, porous polymers/polymer foams can be used as insulation materials, while inorganic or hybrid materials are widely used in heterogeneous catalytic applications. An important parameter that influences the usage and properties of nanoporous polymers is the pore size. However, adjusting and controlling pore sizes is a challenge encountered by scientists nowadays. Recently, the Nanofoams by Continuity Inversion of Dispersion (NF-CID) method has been developed to synthesize nanoporous polymers with adjustable pore sizes (Fig. 1) [1]. 

Scheme of the NF-CID Principle (c)
Figure 1: Scheme of the NF-CID principle. (1) Thermoplastic nanoparticles synthesized by emulsion, miniemulsion, or microemulsion polymerization. (2) Drying the dispersion results in close-packed nanoparticles, which are in step (3) filled with a sc-fluid, decreasing the Tg of the polymer. (4) Increasing the temperature above the lowered Tg *, the octahedral and tetrahedral voids (ideal packing) filled with the sc-fluid transform into spherical nanodroplets in the highly viscous polymer matrix. (5) Expanding the system leads to both foaming and fixation of the polymer. Redrawn from [1]

Following the NF-CID method and within the framework of the Collaborative Research Center CRC 1333 at the University of Stuttgart, we aim to synthesize nanoporous polymers based on polystyrene & poly(methylmethacrylate) with adjustable pore sizes (5 < dpore/nm < 50), geometry and morphology as tailor-made substrates for molecular heterogeneous catalysis in confined geometries. Furthermore, in cooperation with the workgroup of Prof. Dr. J. Bill (Institute of Material Science, workgroup for Bioinspired Materials & Systems) the nanoporous polymers will be subject to a multi-cyclic mineralization reaction [2] to form a layer of metal oxides (e.g. ZnO,ZrO2,SiO2, Al2O3 or TiO2) on the pore walls of the nanoporous polymers (Fig. 2) [3, 4], to which catalysts can finally be attached. 

SEM images - synthesis of hybrid materials from colloidal particles (c)
Figure 2: (Left) SEM image of the close-packed polystyrene nanoparticles. (Middle) SEM images of an interconnected polystyrene foam obtained from the colloidal crystal via a two-step NF-CID process. While the continuity-inversion was performed with scCO₂ at 𝑝 = 250 bar, 𝑇 = 65 °C and an exposure time of 15 min, the expansion step was modified in order to avoid aging processes. (Right) SEM image of the interconnected polystyrene foam/ZnO hybrid material after 10 deposition cycles. [4]

Bicontinuously structured microemulsions consisting of polar and nonpolar nanodomains (liquid confinement) might facilitate the transport of molecules with different polarities into and out of the nanoporous hybrid material. Thus, in cooperation with the workgroup of Prof. Dr. S. Laschat (Institute of Organic Chemistry, University of Stuttgart), microemulsions, e.g. H2O/NaOH, toluene/reactants and the sugar surfactant n-octyl b-d-glucopyranoside (C8G1), are used to study the role of liquid confinement in asymmetric Rh catalysis. As a benchmark reaction, the 1,2-addition of phenylboroxine (2) to N-tosylimine 1 in the presence of [RhCl(C2H4)2]2 and chiral diene ligands was investigated [5].

References

  1. Strey, R., Müller, A.: Patent DE102010053064A1 (2010). https://patents.google.com/patent/DE102010053064A1/en
  2. Lipowsky, P., Hoffmann, R. C., Welzel, U., Bill, J., Aldinger, F.: Site-Selective Deposition of Nanostructured ZnO Thin Films fromSolutions Containing Polyvinylpyrrolidone. Adv. Funct. Mater.17, 2151-2159 (2007). https://doi.org/10.1002/adfm.200600399
  3. Qawasmi, Y., Atanasova, P., Jahnke, T., Burghard, Z., Müller, A., Grassberger, L., Strey, R., Bill, J., Sottmann, T.: Synthesis of nanoporous organic/inorganic hybrid materials with adjustable pore size. Colloid and Polymer Science. 296, 1805--1816 (2018). https://doi.org/10.1007/s00396-018-4402-z
  4. Qawasmi, Y.: Toward Confined Spaces in Polymers and Microemulsions for Catalytic Applications. PhD Thesis (2019). 
  5. Deimling, M., Kirchhof, M., Schwager, B., Qawasmi, Y., Savin, A., Mühlhäuser, T., Frey, W., Claasen, B., Baro, A., Sottmann, T., Laschat, S.: Asymmetric Catalysis in Liquid Confinement: Probing the Performance of Novel Chiral Rhodium–Diene Complexes in Microemulsions and Conventional Solvents. Chemistry – A European Journal. 25, 9464–9476 (2019). https://doi.org/10.1002/chem.201900947

Cooperations

Karina Abitaev
 

Karina Abitaev

PhD Student

Thomas Sottmann
Apl. Prof. Dr.

Thomas Sottmann

Professor

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