Making light work of soft matter materials design
Advanced macromolecular design – ranging from block copolymer formation and end group transformations to surface modification – should be rapid, function under equimolar conditions and preferentially occur at ambient temperatures to allow for a maximum of simplicity as well as – importantly – bioorthogonality. One of our synthetic foci is thus the development of rapid ambient temperature macromolecular transformation processes, which make use of, for example, Diels-Alder chemistry.
Facing limitations of available resources on our planet, it is critical to re-evaluate the way we manufacture essential goods. Nature provides key inspiration for how to produce complex and highly functional materials through the perfectly sustainable, light-fuelled process called photosynthesis. While human technology still has a long way to go to achieve nature’s sophistication, the Soft Matter Materials Laboratory pioneers fundamentally new approaches in synthesis that exploit the selectivity and efficiency of light. Avoiding usually required harmful UV light in light fuelled reaction processes, we are constantly developing new polymerization and ligation techniques that make use of benign visible light. Exceeding the spatio-temporal control of light that allows to control when and where a reaction takes place, we are designing chemical reactions that also respond selectively to the colour of light. Such wavelength-gated systems enable molecular surgery by altering specific parts of molecules while leaving others untouched – and on the materials level even enable the fabrication of multiple materials from only one photoresist as the function of the colour of light. Addressing the global problem of lifetime cycles of polymers, we are developing polymers that can be unmade again in the presence of a certain stimulus. Taking lifetime control of synthetic materials one step further, we synthesize chemical bonds that are only stable in the presence of light and autonomously disintegrate in the dark. Inspired by nature’s functional macromolecules such as enzymes, we develop synthetic avenues to generate functional 3D architectures from synthetic polymer chains, so called single chain nanoparticles.
In combination with ring-opening polymerization (ROP) or reversible deactivation radical polymerization techniques such as atom transfer radical polymerization (ATRP) or reversible addition-fragmentation chain transfer (RAFT) polymerization, our light-induced tools provide the opportunity for the rapid design of complex macromolecular under ambient reaction conditions. Our light triggered ligation protocols include the NITEC (nitrile imine tetrazole ene cycloaddition) approach, photo-triggered oxime ligations, several variants of photoenol and phenacylsulfide chemistry or photochemical approaches based on phencyclones. Importantly, the developed toolbox of light triggered reactions finds applications in our activities in hybrid material design, most notably for spatially resolved (bio)surface design and in lithographic applications such as 3D laser lithography, i.e. Direct Laser Writing (DLW).
The in-depth understanding of underlying reaction mechanisms and kinetics is a critical part of effectively modelling and predicting polymerization processes. Within the Soft Matter Material Laboratory, the use of PREDICI software as well as pulsed laser polymerization coupled with absolute molecular weight analysis (PLP-SEC) are combined for the simulation and experimental determination of fundamental polymerization processes, from propagation and termination rates, molecular weights, or sequence distribution to the initiation processes or efficiencies of photoinitiator systems.