Visible-light reversible photopolymerisation: insights via online photoflow – electrospray ionisation – mass spectrometry

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. Both a batch approach and a continuous photoflow setup are employed to investigate the degree of polymerisation and scalability. Violet blue light at 415 nm triggers [2 + 2]-cycloadditions of a pyrene-chalcone derivative to grow linear step-growth polymers, while subsequent UV-B light irradiation triggers the depolymerisation. The process was monitored online via a photoflow – high resolution electrospray ionisation mass spectrometry setup (ESI-MS). Size exclusion chromatography provides additional offline analysis of both the polymerisation and photodegradation over time. 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.