Photo-Induced Polymerization Reactions: Quantitative Information via Mass Spectrometry and Femtosecond Pump-Probe Absorption Studies

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The current extension request builds on the work of the past 2.5 years funded by the DFG on the topic of Quantifying the Reactivity of Photolytically Generated Radicals Towards Vinylic Monomers via Electrospray Ionization Mass Spectrometry (ESI-MS), where the foundation was laid for achieving an in-depth quantitative understanding of photo-initiation processes via the provision of relative net initiation ratios associated with individual radical fragments originating from various photoinitiators. In the course of the research we found unexpectedly that femtosecond spectroscopy in combination with the pulsed laser polymerization size-exclusion chromatography ESI-MS (PLP-SEC-ESI-MS) experiments yield not only insights into the relative net efficiency of a radical fragment, but also allows to correlate the observed net efficiencies with the internal energy distribution within the excited molecule, i.e. the efficiency of the singlet to triplet intersystem crossing after laser excitation. The original grant has led to the study of 9 initiation systems leading to 4 peer-reviewed research outputs (as well as additional forthcoming manuscripts) that highlight the power of our combined experimental approach to for the first time generate quantitative knowledge about net efficiencies of photoinitiators with their internal energy dissipation channels. Within the requested extension project, we now wish to exploit our combined experimental set-up in a collaborative project between the KIT Polymer and Physical Chemistry institutes. The key aim is the quantitative determination of the relative net initiation efficiency via the now established PLP-SEC-ESI-MS technique for a wide range of radical fragments coupled with the quantitative understanding of the intersystem crossing behavior of the constituting initiator molecules, to arrive at a map of origin dependent radical fragment initiation efficiencies. We believe that a unique opportunity exists to for the first time provide a full and comprehensive understanding of final polymer end group distribution of photolytically generated radical fragments with the structure dependent internal energy conversion within the photoinitiators.