Solar Flow Synthesis of Polymer Nanoparticles: Scaling Local Experiments to Global Potential.

We present the scalable, additive-free synthesis of polymer nanoparticles in continuous flow, using solely solar radiation. Using a custom-made flow reactor, the UV radiation from the sun induces a Diels-Alder step-growth polymerization between a bismaleimide and a difunctional o-methylbenzaldehyde. The resulting photopolymer subsequently precipitates as nanoparticles without the need for any additional additives, stimuli or processing steps. The solar flow reactor was designed by first carefully assessing the underpinning photochemistry of the photo-induced Diels-Alder reaction using photochemical action plots and then performing a kinetic investigation of the particle formation under solar irradiation. The determined kinetics allow us to extrapolate our experimental results to a worldwide particle yield by using global UV index data, validated by two highly different geographical locations, Australia and Germany. Our results clearly demonstrate the applicability of our system for the scalable, sustainable, solar-powered production of polymeric nanoparticles in regions of high levels of solar radiation. Furthermore, our calculations function as a blueprint for how local experimental data can be extrapolated to assess the global solar photochemical potential of photochemical systems, thus making their performance comparable.