Extremely deep photopolymerization using upconversion particles as internal lamps
Although photopolymerization has been versatile in various applications, photopolymerization of thick materials still remains a great challenge due to the light-intensity gradient. In this paper, we report a facile and generic method to realize deep photopolymerization using upconversion nanoparticle (UCNP)-assisted photochemistry. Compared to the reported photocuring depth of several millimeters, 13.7 cm of photopolymerization depth combined with about 60% of double bond conversion is obtained with optimal parameters. The thermal effect during UCNP-assisted photopolymerization is comparable to or weaker than that of some reported frontal photopolymerization used for the preparation of dental filling materials and functional polymer composites. The photocured materials using UCNPs as internal lamps exhibit a similar nanoindentation hardness and reduced modulus to those cured under traditional blue LED light. The presented strategy shows great potential applications in ultra-high density data storage and the preparation of biomaterials.