Counting the Clicks in Fluorescent Polymer Networks

We introduce a fluorescence‐based methodology enabling the quantification of ligation points in photochemically prepared polymer networks. Well‐defined α,ω‐tetrazole‐capped polymer strands prepared via RAFT polymerization are crosslinked under UV irradiation by a trimaleimide via nitrile imine mediated tetrazole–ene cycloaddition. Thus, for each linkage point a fluorescent pyrazoline ring is formed, resulting in fluorescent networks, which are degradable by aminolysis of the trithiocarbonate functionalities, leading to soluble fragments. The fluorescence emission of the soluble network fragments correlates directly with the number of pyrazoline moieties originally present in the network, thus providing a direct measure of the number of ligation points constituting the network. The herein introduced strategy based on a fluorescence readout is a powerful yet simple approach to quantify network formation processes applicable to a wide class of polymers accessible via RAFT. Lights on for every link: The number of linkages in polymer networks can be quantified by exploiting the fluorescent properties of pyrazoline units. These units are generated during network formation, with each unit providing a countable fluorescent readout tag. This methodology was used to determine the exact number of linkage points constituting a network and is applicable to a wide range of RAFT‐based polymers.