Structure-Reactivity Relationships of Oxime-Oxalate/Glyoxylate/Ester Derivatives: Dual Photo/Thermal Initiators for Visible Light Polymerization and Composite Preparation.

In this study, we reported the design, synthesis, and comprehensive evaluation of a series of nitro carbazole-based oxime photoinitiators (OPIs, OP1: oxime oxalate, OP2: oxime glyoxylate), as a series of efficient Type I photoinitiators (PIs) for the free radical photopolymerization (FRP) of trimethylolpropane triacrylate (TMPTA) and ethoxylated trimethylolpropane triacrylate (ETPTA) under blue light-emitting diodes and sunlight irradiation. Computational molecular modeling was employed to predict the effect of OPIs structures on the photoinitiation properties. The predictions suggest that OP1 had a higher propensity for decarboxylation and therefore a better photoinitiation behavior. Compared to OP2, OP3, and commercial benchmark photoinitiator TPO, OP1 exhibits exceptional photoinitiation performance when exposed to LED@405 nm, LED@450 nm, and sunlight. OP1 undergoes decarboxylation to efficiently produce CO2 and free radicals, thereby initiating the photopolymerization reaction. Remarkably, OP1 is successfully applied in 3D printing, producing complete morphology with high-resolution structure, showcasing its potential for advanced manufacturing applications. The photochemical mechanism of OPIs is comprehensively elucidated using the monitoring of the CO2, steady state photolysis, UV-vis absorption spectroscopy, fluorescence spectroscopy, and electron spin resonance techniques. These experimental investigations are supported by data OP1 from the molecular modelling carried out. Additionally, thermal polymerization shows that OP1 had a high thermal initiation capability, and the composites are successfully prepared together with carbon fibers. The cytotoxicity of the synthesized oxime oxalate and TPO on human umbilical vein endothelial cells (HUVECs) results in a lower cytotoxicity for the oxalate than for TPO. Therefore, OP1, which has never been reported before, can be used as a highly efficient and low cytotoxic dual photo/thermal initiator. This research not only provides theoretical and practical insights into the design and development of new efficient Type I PIs, but also opens up new perspectives for curing applications that require scalability, cost-effectiveness, environmental sustainability, and green chemistry.