Multimaterial\nThermoset Synthesis: Switching Polymerization\nMechanism with Light Dosage

The synthesis of polymeric thermoset materials with spatially\ncontrolled\nphysical properties using readily available resins is a grand challenge.\nTo address this challenge, we developed a photoinitiated polymerization\nmethod that enables the spatial switching of radical and cationic\npolymerizations by controlling the dosage of monochromatic light.\nThis method, which we call Switching Polymerizations by Light Titration\n(SPLiT), leverages the use of substoichiometric amounts of a photobuffer\nin combination with traditional photoacid generators. Upon exposure\nto a low dose of light, the photobuffer inhibits the cationic polymerization,\nwhile radical polymerization is initiated. With an increased light\ndosage, the buffer system saturates, leading to the formation of a\nstrong acid that initiates a cationic polymerization of the dormant\nmonomer. Applying this strategy, patterning is achieved by spatially\nvarying light dosage via irradiation time or intensity allowing for\nsimple construction of multimaterial thermosets. Importantly, by the\naddition of an inexpensive photobuffer, such as tetrabutylammonium\nchloride, commercially available resins can be implemented in grayscale\n vat photopolymerization 3D printing to prepare sophisticated multimodulus\nconstructs.