Photopolymerization activated by photobase generators and applications: From photolithography to high-quality photoresists

Light-induced polymerization has become a very attractive technology for advanced manufacturing of polymers. In fact, the photopolymerization processes, and even the final properties of the polymerized materials, are determined by the photoinitiator (PI), which is the key component that generates the active species during irradiation. Among the many photoactive compounds utilized as PIs, photoacid generators (PAGs) and photobase generators (PBGs) efficiently generate the bases or acids required to activate polymerization. Despite the obvious advantages of PAGs, PBGs exhibit wavelength specificity, better photostability, excellent compatibility with a wider range of monomers, etc. Furthermore, these organic compounds promote photopolymerizations followed by various photochemical processes encompassing ring-opening polymerization, the thiol–epoxy click reaction and thiol-Michael addition. With the aim of expanding the number of available PBGs, intensive research has been devoted in the last decade to designing and synthesising PBGs that promote photopolymerization with higher initiation capacities. In this review, we systematically discuss the recent advances made with organic PBGs during 2019–2023 to provide deeper insight into these photoactive compounds and broaden their application.