Photoinitiated Wavelength–Selective Two Stage Polymerization

AbstractOwing to its unique spatial and temporal control, photochemistry has been widely adopted as a highly efficient tool in photopatterning fabrication and polymer synthesis. The thiol–isocyanate reaction, typically base–catalyzed is considered as a “click” reaction due to its high efficiency under mild condition. In this study, we employ a highly efficient photo latent tertiary amine to initiate the thiol–isocyanate reaction, thereby integrating photochemical activation with thiol–click chemistry to achieve a “photo–click” system. This photoinitiated thiol–isocyanate reaction enables the formation of polymer networks with relatively high glass transition temperatures and refractive indices, offering precise spatiotemporal control. Given the orthogonality of their mechanisms: radical–mediated for thiolene and base–catalyzed for thiol–isocyanate–the two reactions could be performed sequentially using visible and UV light irradiation. By exposing formulations containing varied molar ratios of thiol, allyl and isocyanate groups to specific wavelengths, we monitored and confirm the two–stage photopolymerization processes through real–time Fourier transform infrared (FTIR) spectroscopy conversion plots.