Quinoline-based Photoinitiators for Vat Photopolymerization: Synthesis and Formulation Design for 3D Printing

Quinoline derivatives (Q-OMe and Q-SMe) were synthesized via a green one-pot multicomponent reaction and evaluated as photoinitiators for urethane dimethacrylate (UDMA) photopolymerization. Their performance was investigated under UV (370 nm) and blue (456 nm) irradiation, in the presence and absence of ethyl p-dimethylaminobenzoate (EDB). Blue light led to significantly higher conversions (up to 73%) compared to UV irradiation (<5%). Statistical analysis confirmed that both the photoinitiating system and photoinitiator concentration significantly affected the final monomer conversion, with the Q-SMe/EDB system consistently exhibiting the highest conversion values. UV-vis and mass spectrometry provided evidence for the formation of a sulfoxide intermediate during Q-SMe photoactivation, supporting the proposal that this derivative can operate through both type I and type II photoinitiation pathways, whereas the photochemical behavior of Q-OMe is consistent with a predominantly type II mechanism. The optimized Q-SMe/EDB formulation (0.3 wt % Q-SMe/0.5 wt % EDB) was subsequently applied to UDMA/TEGDMA resins for vat photopolymerization, where increasing the TEGDMA content increased the penetration depth (138-172 μm) while reducing the monomer conversion. Under identical printing conditions, the optimized Q-SMe/EDB formulation produced well-defined 3D structures without overcuring, unlike the conventional CQ/EDB system. These results demonstrate the potential of quinoline-based photoinitiating systems for visible-light vat photopolymerization of methacrylate resins and highlight the importance of exploring new quinoline derivatives for the development of efficient photoinitiating systems.