By simply increasing the run time of the flow reactor, larger amounts of the desired product can be acquired in a straightforward way without any additional effort. By changing the colour of light, photopolymers can be recycled and reshaped, allowing these macromolecular precursors to be applied to reversible and photodegradable material design. Continuous photoflow as a setup for sequence-defined macromolecular synthesis is a powerful approach to obtain near gram quantities of precision oligomers. Size exclusion chromatography provides additional offline analysis of both the polymerisation and photodegradation over time. The process was monitored online via a photoflow – high resolution electrospray ionisation mass spectrometry setup (ESI-MS). Violet blue light at 415 nm triggers -cycloadditions of a pyrene-chalcone derivative to grow linear step-growth polymers, while subsequent UV-B light irradiation triggers the depolymerisation. Both a batch approach and a continuous photoflow setup are employed to investigate the degree of polymerisation and scalability. The final step is a simple acylation reaction with the formation of fentanyl as its hydrochloride salt (commercialized form) or free base. Herein, we demonstrate the scalable synthesis of catalyst-free, visible-light mediated photo-oligomers and -polymers via a step-growth mechanism. The first two steps are promoted by visible light photoredox catalysis, both being translated from batch and scaled up under continuous flow conditions with telescoping. Light as a non-invasive and clean external stimulus provides a facile route towards macromolecular design. Herein, we demonstrate the scalable synthesis of catalyst-free, visible-light mediated photo-oligomers and -polymers via a step-growth mechanism.
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