Visible-Light Emulsion Photopolymerization of Styrene.

The photopolymerization of styrene in emulsion is achieved in a conventional double-wall reactor equipped with a LED ribbon coiled around the external glass wall. Styrene mixed to acridine orange is added to the water phase containing sodium dodecyl sulfate, a water-soluble N-heterocyclic carbene-borane and disulfide, and irradiated. Highly stable latexes are obtained, with particles up to a diameter of 300 nm. The ability to reach such large particle sizes via a photochemical process in a dispersed medium is due to the use of visible light: the photons in the visible range are less scattered by larger objects and thus penetrate and initiate better the polymerizations. They are also greener and cheaper to produce via LEDs, and much safer than UVs. The method presented does not require any specific glassware; it works at lower temperature and delivers larger particles compared to thermal processes at similar solids contents and surfactant concentrations.