I joined the theory group at the Max Planck Institute for Polymer Research as a postdoc in May
2017. My current research focusses on the exciton transport and upconversion in organic materials.
I obtained my PhD in computational chemistry with special distinction from Jacobs University
under the supervision of Prof. Thomas Heine. My PhD thesis focused on understanding electronic
structure of atomic clusters and reaction mechanism for organic reaction by mean of density
functional theory and ab initio molecular dynamics. After that, I carried out my first postdoc
position with Prof. Stefan Grimme at University of Bonn from May 2015 to April 2017, mainly
working on computational chemistry of so-called “frustrated Lewis pairs” in solution and in solid
Published in the group
Mechanistic study on the hydrolytic degradation of polyphosphates
K. Bauer, L. Liu, M. Wagner, D. Andrienko, F. Wurm
European Polymer Journal,
Ring-opening polymerization of cyclic phosphates offers a fast access to well-defined water soluble and (bio)degradable polyphosphoesters (PPEs). In particular poly(alkyl ethylene phosphate)s have been used as building blocks for nanocarriers or hydrogels. The molecular mechanism of their degradation is however not well understood. Herein we study the hydrolytic degradation of two most frequently used PPEs poly(methyl ethylene phosphate) (PMEP) and poly(ethyl ethylene phosphate) (PEEP). The degradation process is analyzed by NMR spectroscopy which identifies and quantifies intermediates and degradation product(s). We prove that the major degradation pathway is backbiting leading to one dominating hydrolysis product ethyl or methyl ethylene phosphate (a diphosphate). Accelerated hydrolysis performed in basic and acidic conditions shows the high stability of PEEs under acidic conditions while they readily degrade under basic conditions. The backbiting mechanism is further supported by the reduction of the degradation kinetics if the terminal OH-group is blocked by a urethane. Our findings help to develop degradable nanodevices with adjustable hydrolysis kinetics.
Alcohol- and water-tolerant living anionic polymerization of aziridines
T. Gleede, E. Rieger, L. Liu, C. Bakkali-Hassani, M. Wagner, S. Carlotti, D. Taton, D. Andrienko, F. Wurm
Living anionic polymerization gives access to well-defined polymers but it demands strict purification of reagents and solvents. This work presents the azaanionic polymerization (AAROP) of aziridines as a robust living polymerization technique with the ease of controlled radical polymerizations. AAROP does not require inert atmosphere and remains living in the presence of large amounts of water or alcohols. Mesyl- tosyl- or brosyl-activated aziridines were polymerized with up to 100-fold excess of a protic impurity with respect to the initiator and still being active for chain extension. This allowed the preparation of polyols by anionic polymerization without protective groups as only minor initiation occurred from the alcohols. The tolerance toward protic additives lies in the electron-withdrawing effect of the activating groups decreasing the basicity of the propagating species while maintaining a strong nucleophilic character. In this way competing alcohols and water are only slightly involved in the polymerization making living anionic polymerization an easy-to-conduct technique to well-defined polyamides and -amines.
Polymerizing phostones: A fast way to in-chain poly(phosphonate)s with adjustable hydrophilicity
K. Bauer, L. Liu, D. Andrienko, M. Wagner, E. Macdonald, M. Shaver, F. Wurm
Phostones i.e. 2-alkoxy-2-oxo-13-oxaphospholanes are accessible in a one-pot reaction from commercially available 13-dibromopropane and alkyl phosphites. These 5-membered cyclic phosphonic acid esters are used for the preparation of linear poly(phosphonate)s via ring-opening polymerization resulting in polymers with a hydrolytically stable P-C bond in the polymer backbone. Phostones have the stable P-C bond within the cycle which leads to a dramatic increase of the monomer stability toward hydrolysis and long shelf-lives compared to other cyclic phosphoesters which hydrolyze immediately at contact with water. Two phostone monomers containing ethoxy or butoxy pendant chains were prepared in a single-step synthesis from inexpensive starting materials avoiding the usage of SOCl2 or POCl3. Polymers with ethoxy side chains are water-soluble without a lower critical solution temperature nontoxic to murine macrophages and hydrolytically degradable under basic conditions. The polymerization kinetics for different catalyst systems were evaluated for both monomers in order to identify optimal polymerization conditions resulting in polyphosphonates with molecular weights between 3000 and 25 100 g/mol with reasonable molecular weight dispersities (<1.6). Because of the ease of synthesis and distinct different hydrolysis kinetics compared to side-chain polyphosphonates we believe that these new polyphostones represent a valuable addition to water-soluble biopolymers for future biomedical applications.