Research Interests

Polymers with dendritic side chains radiating from the polymer backbone were first described in a patent by Tomalia in the late 1980s.[1] In the 1990s, Fréchet and Hawker extended the original concept to the synthesis of dendritic-linear copolymers [2] and Percec et al. explored the use of linear polymers with "tapered" side chains for their phase behavior in bulk.[3] The term "dendronized" polymers (DPs) was coined by Schlüter and co-workers and they, over the years, showed that these polymers can be considered cylindrical molecular objects (Figure 1).[4,5,6] Their shape persistence as well as the very large number of end groups accessible for functionalization fuels the growing interest in this special class of structurally well-defined, regularly branched macromolecules with ultrahigh total molar mass.[7,8] To give but one example for their potential impact, covalently attached to pharmaceuticals, such branched polymers can act as protracting agents aiming at improving pharmacokinetic- and pharmacodynamic properties.[9,10]

An attractive strategy for the preparation of DPs with a minimum of synthesis steps relies on the use of bi-, tri or multi-furcated monomers in a stepwise, repetitive reaction sequence leading theoretically to unimolecular and monodisperse oligomerisation products (polymer generations, PG) (Figure 2).[11] The synthetic procedures developed allow for nearly complete control over critical molecular design parameters such as size, shape as well as surface- and interior chemistry. This way, the representatives of such a homologous series allow for systematic, generation-dependent studies of structure-property relationships.

Furnishing DPs with chemically different dendron motifs (pathway d in Figure 2) allows for the preparation of multifunctional, responsive materials and offers an opportunity to control and investigate their intermolecular interactions (Figure 3).[12,13] Although the use of DPs has been proposed and reported for manifold purposes, the details of their rheological response, which governs their final properties in applications, remain elusive. It has been proposed that DPs resemble weakly interpenetrating, elongated core-shell systems, whose rheological dynamics appear to be particularly dominated by the enhanced rigidity and strong intermolecular forces that increase with higher generations.[14] Controlling these non-covalent interactions by chemical modification of the DPs outer surface could be a useful strategy and of particular significance for tailoring the rheological response of DPs. In this context, novel, structurally well-defined hybrid DPs and their precursors are synthetized and their structures and properties are determined by methods of analytical chemistry, e.g. nuclear magnetic resonance (NMR) spectroscopy or mass spectrometry (MS) and materials analysis techniques such as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC) and atomic force microscopy (AFM). Additionally, the linear and non-linear rheological properties of these DPs are measured in collaboration with renowned experts in the field (group of Prof. Dr. D. Vlassopoulos, Crete).

Further Reading

[1] D. A. Tomalia, P. M. Kirchhoff , Rod-shaped dendrimers, Eur. Pat. Appl. 234408, Sep 2, 1987.
[2] Fréchet et al., Polymer 1992, 33, 1507-1511.
[3] Percec et al., Nature 1998, 39, 161-164.
[4] Schlüter et al., Angew. Chem. Int. Ed. 2000, 39, 864-883.
[5] Schlüter et al., Angew. Chem. Int. Ed. 2011, 50, 737-740.
[6] Schlüter et al., ACS Macro Lett. 2014, 3, 991-998.
[7] Bell et al., Science 1996, 271, 1077-1078.
[8] H. Frauenrath, Prog. Polym. Sci. 2005, 30, 325-384.
[9] Fréchet et al., Nat. Biotech. 2005, 23, 1517-1526.
[10] Kochendoerfer et al., Science 2003, 299, 884-887.
[11] Schlüter et al., J. Am. Chem. Soc. 2009, 131, 11841-11854.
[12] Fréchet et al., J. Am. Chem. Soc. 2000, 122, 10335-10344.
[13] Percec et al., Chem. Eur. J. 2008, 14, 3355-3362.
[14] Pasquino et al., Macromolecules 2012, 45, 8813-8823.

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