Wavelength-Selective Sequential Polymer Network Formation Controlled with a Two-Color Responsive Initiation System

We report a wavelength-selective polymerization process controlled by visible/UV light, whereby a base is generated for anion-mediated thiol-Michael polymerization reaction upon exposure at one wavelength (400-500 nm), while radicals are subsequently generated for a second stage radical polymerization at a second, independent wavelength (365 nm). Dual wavelength, light controlled sequential polymerization not only provides a relatively soft intermediate polymer that facilitates optimum processing and modification under visible light exposure but also enables a highly cross-linked, rigid final material after the UV-induced second stage radical polymerization. A photobase generator, NPPOC-TMG, and a photo-radical initiator, Irgacure 2959, were selected as the appropriate initiator pair for sequential thiol-Michael polymerization and acrylate homopolymerization. FT-IR and rheological tests were utilized to monitor the dual cure photo-polymerization process, and mechanical performance of the polymer was characterized at each distinct stage by dynamic mechanical analysis (DMA). By demonstrating complete light control in another sequential polymerization system (thiol-Michael and thiol-ene hybrid polymerization), this initiator pair exhibits great potential to regulate many other coupled anion and radical hybrid polymerizations in both a sequential and controllable manner.