Visible-Light-Sensitized Photo-Oxidative Cross-Linking Of Polysiloxanes Using Singlet Oxygen

Photo-cross-linking of polymeric materials generally requires an inert atmosphere because of oxygen-based inhibition and quenching of the reactive species. Here, we demonstrate the photo-oxidative cross-linking of amine-functionalized poly(dimethylsiloxane) using atmospheric oxygen as the chemical oxidant. Visible light irradiation of a metalloporphyrin or an organic sensitizer generates reactive singlet oxygen that oxidatively couples amines into imine cross-links. This facile benchtop cross-linking reaction proceeds at room temperature and results in solvent-free elastic materials after 1 h. Solid state C-13 nuclear magnetic resonance and Fourier transform infrared spectroscopy show that the reaction produces only imine functionalities with no side products observed. The mechanical properties of these polymers were tested using tensile experiments and were found to depend on the initial loading of the sensitizer, with a maximum elongation strain of 157% and a Young's modulus of 2.15 MPa for the highest tested amount. Photolithography is demonstrated with this cross-linking system using visible light irradiation.