The efficiency of photoinitiators in ionic liquids

• Absorption properties of photoinitiators differ in ILs and in organic solvents.
• Ionic liquids can influence the cleavage reaction of photoinitiators.
• The photolysis quantum yield can drop drastically in ionic liquids.
• Effectiveness of a photoinitiator depends on the structure of the IL used.

In this work, efficiency of initiation of the photopolymerization in ionic liquids (ILs) by four Type I photoinitiators (PIs) was investigated. The influence of the ILs on the initiation process was determined by investigation of the polymerization kinetics and by spectroscopic and photolysis studies. The polymerization initiated by three of the tested PIs proceeded faster in ionic liquids, whereas the efficiency of the photoinitiator depended strongly on the structure of the ionic liquid. In one case, (2-methyl-4′-(methylthio)-2-morpholinopropiophenone), there was a significant reduction in the reaction rate, which resulted from a drastic decrease in the quantum yield of photolysis of this photoinitiator in ionic liquids. The results obtained suggest that for every composition containing an ionic liquid, the photoinitiator should be matched individually.

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