Photo-Triggered End-Group Conversion of Synthetic Polymers Prepared via Light-Induce

In the proposed project, an Austrian (Graz University of Technology) and a German group (Karlsruhe Institute of Technology, KIT), with a complementary set of skills, join forces for the in-depth study of photolytically triggered radical transformation pathways of synthetic polymers generated via photoinitiation processes. The aim of the project is to arrive at an encompassing mechanistic understanding of the underpinning reactions that occur when well-defined photolytically generated synthetic polymers are subjected to secondary irradiation processes. Data on such processes is very scarce, yet of paramount importance to (i) judge the propensity of photo-generated polymers to change their end-group characteristics upon post-irradiation or during the primary irradiation process, which can significantly affect their performance and (ii) to exploit UV-triggered end-group transformations for the post- modification of photolytically generated polymers. To obtain the required underpinning mechanistic data, well- defined polymers generated via pulsed laser induced polymerization process will be prepared and subjected to a combination of analytical on-line (in-situ UV-irradiation analysis) and off-line (post UV-irradiation analysis) methodologies, including size exclusion chromatography coupled to mass spectrometry (SEC/ESI-MS), chemically-induced dynamic nuclear polarization (CIDNP) NMR as well as electron paramagnetic resonance (EPR) spectroscopy. The result of the project will be a first-time thorough understanding of the radical end-group transformation pathways for a series of photoinitiator/monomer systems and the establishment of guiding principles that dictate these processes as a function of the photolytically introduced end-groups as well as the type of employed monomer.

Coatings have been omnipresent of our everyday life. Several of such coatings have been produced by light-induced procedures. Such layers are utilized for protecting all kinds of surfaces, they are the basis of electronic prints or are produced by dentists as dental fillings (blue light). Such materials must be stable and resistant for a substantially long period of time. They have to withstand mechanical stress chemicals, and, importantly, they also have to be stable versus irradiation with light. In our project, we have gained pioneering insights into the molecular basics of the light resistance of polymers. The light-induced procedures leading to the formation of polymers are based on the properties of a photoinitiator, which is activated by light and leads to the formation of a polymer. The fragments of the photoinitiator constitute the end groups of the polymer. Yet, hardly anything has been known about the role of the end groups for the stability of polymers. With the use of state-of-the-art experimental techniques, e.g. wavelength-dependent pulsed laser techniques and time-resolved spectroscopic methodology in the nanosecond time regime, we have investigated the intrinsic chemical conversions of the end groups in the polymers. We have been able establishing what kind of end groups leads to particularly light resistant polymers. In this context we could moreover show that the reactivity of the end groups and the initiators can be unexpectedly high even at long wavelengths. This can be principally traced back to the substantial penetration depth of light with high wavelengths. In summary, our research has revealed the molecular basics of coatings displaying long lifetimes.