Photocatalytic Disulfide Bond Coupling by Surface-Reduced Manganese Oxide for Controlled Polysulfide-Based Polymer Synthesis

Abstract

Manganese oxide (MnO 2 ) is a commonly used vulcanizing agent, which can convert polysulfide oligomers with reactive terminal mercaptans into polymeric networks. Herein, an elegant approach for the fast and facile curing behavior of polysulfide rubbers was disclosed under visible-light irradiation. Photocatalytic disulfide bond coupling of mercaptan end groups can be achieved on MnO 2 in the presence of visible-light irradiation. More importantly, compared with pristine MnO 2 , surface-reduced MnO 2 (R-MnO 2 ) with abundant Mn 3+ sites and oxygen vacancies exhibited superior vulcanizing performance. Theoretical simulation uncovers that R-MnO 2 can facilitate electron transfer due to a narrowed energy band gap and reduce the energy barriers required for photocatalytic disulfide bond formation. This work opens up the potential of using visible light together with surface modification to tune the vulcanizing process and the properties of polysulfide rubbers.

Rapid, efficient and controllable photo-assisted polysulfide sealing over MnO2

“…O 2 can consume the photo-generated electrons and promote the separation of holes and electrons, thereby improving the reaction activity. 24 Thirdly, δ-MnO 2 is composed of cross-linked nanosheets and exhibits the highest specific surface area, which features more exposed reactive active sites for the curing reaction of liquid PS rubber molecules. 25 Furthermore, the hydroxyl (–OH) content on the surface of δ-MnO 2 is much higher than that of α-MnO 2 and γ-MnO 2 , and –OH plays an important role in the activation of –SH and increases the activity.…”