Designing artificial macromolecules with absolute sequence order represents a considerable challenge. We employ advanced light-induced avenues to monodisperse sequence-defined functional linear macromolecules via unique photochemical approaches. The versatility of our synthetic strategies – combining sequential and modular concepts – enables the synthesis of perfect macromolecules varying in chemical constitution and topology. Specific functions are placed at arbitrary positions along the chain via the successive addition of monomer units and blocks, leading to a library of functional homopolymers, alternating copolymers and block copolymers. The in-depth characterization of each sequence-defined chain confirms the precision nature of the macromolecules. Decoding of the functional information contained in the molecular structure is achieved via tandem mass-spectrometry. Photochemical strategies are a viable and advanced concept for coding individual monomers units along macromolecular chains.

The combination of supramolecular binding principles (such as H-bonding and cyclodextrin host/guest interactions) with precision polymer design enables the generation of responsive polymer structures that we apply in the context of biomimetic materials and delivery system design. At the same time, the synthesis of such systems is one of our strength, specifically the synthesis of supramolecularly connected polymers by combining living/controlled polymerization protocols (such as the RAFT process or ATRP) with cyclodextrin host/guest chemistry and (orthogonal) hydrogen bonding systems. A particular emphasis lies not only on the design of unipolar supramolecular polymer systems, yet also on the self-assembly processes induced by supramolecular amphiphilic block copolymers, including systems that can undergo transitions from amphiphilic to non-amphiphilic at a certain temperature. The architectures that are prepared include AB, ABA block copolymers, H-shaped polymers as well as (mikto)arm star polymers.

Free radical polymerization has been revolutionized by the advent of methodologies that can significantly extend the lifetimes of the propagating radicals and minimize termination products, thus providing access to well-defined polymer structures with pre-determined molecular weights and low polydispersities. Most importantly, these protocols can be employed to construct complex macromolecular architectures of variable shape and form ranging from linear block copolymers to star and palm-tree like structures. We enjoy generating interesting and complicated polymer structures via sophisticated chemistries, including the development of novel controlling concepts. However, it is also important to develop methods which can arrive at complex architectures in straight-forward fashions, using few reagents and those preferably in one pot reactions. Typical examples of chemistries that we have developed in this field include a one pot reversible addition fragmentation (RAFT)/ring opening polymerization (ROP) process or mechanistic switches between different controlling concepts (such as RAFT and ROP) that give facile access to comb, block or block copolymers featuring degradable and non-degradable polymer strands. Other approaches include the initiator free fabrication of polymerizable macromonomers and their subsequent usage as macromolecular scaffolds in conjugation reactions or even facile transitions of end groups generated by the RAFT process (so-called RAFT to OH terminal switch). Typically, the polymerization concepts are combined with a ligation process and contribute significantly to our research program into hybrid material design.

While we rely on existing control methodologies for polymerization processes, we constantly strive to expand the existing technologies (e.g. by the design of novel functional and (photo)reactive reagents for reversible addition fragmentation chain transfer (RAFT) chemistry) or develop entirely new approaches to effectively control the position and polydispersity of the molecular weight distribution of variable (functional) polymers. Typical examples include polymerization control via spin trapping reagents (e.g. thioketones or nitrones). In addition, we strive to develop photochemically driven methodologies for the synthesis of sequence defined macromolecules, exploiting the orthogonality of light and thermally driven click ligation protocols.

Inspired by the emerging applications of fullerenes and CNTs in nanotechnology, photo-electronics, optics and in the field of nanocomposites, we are interested in covalent surface-functionalization strategies of these materials. Fullerenes and carbon nanotubes act as dienophiles when mixed with an appropriate diene (cyclopentadienyl) end-capped polymer chain. In a one-pot reaction the chains are covalently grafted and thus impart physical and chemical properties of the attached polymer to the nanoobjects. Our strategy – based on a single Diels-Alder reaction – will provide opportunities to be applied for electronic devices and processing methods when modifying a polymer matrix with functional CNTs. Our CNT research program is carried out in cooperation with the Fraunhofer Institute of Technology (ICT) in Pfinztal as well as with groups at the KIT.

To develop an effective synthetic approach to polymers with well-defined properties, an in-depth understanding of the underpinning reaction mechanism and kinetics is important. when the reaction mechanism of a polymerization (including the rate coefficients that govern the individual rate coefficients) is known, one can compute the entire polymerization process including the molecular weight and sequence distribution in advance without ever entering a laboratory. In our group, we use the powerful PREDICI software package to model polymerization processes and deduce kinetic rate coefficients of key reaction steps in a close interplay between experiment and simulation. Key objects of interests are the formation processes of complex architecture polymers (such as stars) and the understanding of acrylate reaction kinetics.

A convenient route to generate free radicals – both industrially and academically – is via ultraviolet (UV) initiated processes. Typically, radical fragments are generated by either the direct formation of radicals from solvent and/or monomer units or by the decomposition of an added photoinitiator molecule. UV initiated polymerization – whilst having industrial applications in the curing of coatings – has especially been employed in conjunction with pulsed UV-laser initiation to obtain propagation and termination rate coefficients via the so-called pulsed laser polymerization – size exclusion chromatography (PLP-SEC) and single pulse – pulsed laser polymerization (SP-PLP) techniques. in the context of these techniques, initiation processes have been studied and the reactivity of the generated initiator radical fragments has been estimated. We employ soft ionization ms techniques to accurately map the groups generated under well-defined UV laser initiated polymerizations; the results support the idea that some initiators generate fragments of very variable reactivity, e.g. an initiator fragment that is mainly responsible for initiation processes and one which is almost exclusively undergoing termination. It is the aim of this research strand to employ SEC-ESI-MS to map UV initiated polymerizations with respect to the generated polymer end groups for a range of initiator systems as well as monomers in solvent and bulk systems. The overall aim is to arrive at a quantitative map of how photolytically generated radical fragments react with specific vinyl double bonds. Molecular weight control in UV-initiated systems (so that molecular weight of the polymers is suitably low for ESI-MS analysis) can be achieved via the RAFT processes (provided the RAFT agent is chosen judiciously to not decompose under UV radiation) as well as via the fast pulsing action of a UV laser. The results from the mass spectrometric investigations are combined with femto-second pump-probe experiments carried out in collaboration with the Physical Chemistry department at the KIT.

The analysis of complex macromolecular architectures is a key activity in synthetic polymer science. in our group, we thus apply and develop methodologies based on 2 dimensional chromatographic techniques for the analysis of advanced polymeric materials that we have synthesized. One of our favorite approaches is liquid adsorption chromatography under critical conditions (LACCC) coupled to size exclusion chromatography (SEC). Via LACCC-SEC, it is possible to image both the chemical and molecular weight heterogeneity of a polymer sample in a precise fashion. Knowledge about both parameters is especially important for the optimization of block copolymer synthesis via modular (ambient temperature) ligation chemistries, yet also in the mechanistic understanding of polymerization processes.