Project
Blockcopolymers and unimolecular micelles for the hydrothermal synthesis of mesoporous silica

Prof. Dr. H. Menzel
Institut für Technische Chemie
Technische Universität Braunschweig

Porous materials can be obtained by hydrothermal synthesis employing organic molecules as porogens [1,2]. The use of supramolecular aggregates like surfactant micelles is of particular interest, since it results in mesoscopic pores (20 - 100 nm) [2]. Amphiphilic blockcopolymers also can be used as porogens, and allow a better control of the pore size and distribution [3,4]. The porogens, polymers and surfactants, are removed in the calcinations process.

It is planned to synthesize unimolecular polymer structures that can serve as a porogen and have a functional polymer as a core. By the tailoring the shell of the polymer structures in terms of the thermal stability, one can obtain different hybrids. If the shell is rather stable the pores of the inorganic material will be completely filled, however, if the shell is thermally unstable hybrid, material will be obtained with only the functional polymer in the pores.

Goal of the synthetic efforts are block copolymers, which are aggregating into micellar structures and can be used as a template in the hydrothermal synthesis of Silica. In particular interesting are polymers comprising nitrogen containing groups, which can be transferred into kationic groups (e.g. polyamines). Such structures can be obtained by combination of ring opening polymerization of oxazolines with corresponding (macro)initiators.

Certain polyamines play an important role in the silica bio-mineralization in diatoms [5]. Because of their polyelectrolyte character these polyamines show strong interaction with the ionic intermediates in the condensation of silicic acid and the silica sol. Furthermore, the significant aggregation of the polyamine in the presence of multivalent anions results supramolecular structures, which significantly influence the structure formation and morphology of the silica. Amphiphilic polyamines or block copolymers having a polyamine block as structure directing agent therefore should result in new porous materials. Beside the „simple” block copolymers also unimolecular polymer structures shall be prepared e.g. star-shaped block copolymers. All polymers have to be characterized and then shall be tested in the hydrothermal synthesis of silica. The resulting hybrid materials have to be investigated.

Literature:
1. C.T. Kresge, M.E. Leinowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359, 710 (1992)
2. J.Y. Ying, C.P. Mehnert, M.S. Wong, Angew. Chem. Int. Ed. Engl. 38, 56 (1999); Angew. Chem. 38, 58 (1999)
3. C.G. Göltner, M. Antonietti, Adv. Mater. 9, 431 (1997)
4. C.G. Göltner, S. Henke, M.C. Weißenberger, M. Antonietti, Angew. Chem. Int. Ed. Engl. 37, 613 (1998), Angew. Chem. 110, 633 (1998)
5. N. Kröger, R. Deutzmann, C. Bergsdorf, M. Sumper, Proc. Nat. Acad. Sci. USA 97, 14133 (2000)