A novel biopolymeric photoinitiator based on chitosan and thioxanthone derivative: Synthesis, characterization and efficiency in photopolymerization

• A novel biopolymeric photoinitiator (TXICh) was synthetized from chitosan.
• TXICh structure was characterized by 1D and 2D NMR experiments.
• Excited state is responsible for producing radicals, which initiate polymerization.
• TXICh showed ability and efficiency of to act as radical photoinitiator.

A novel biopolymeric photoinitiator was synthetized from N-phthaloyl chitosan. The 10-oxo-10H-dibenzene thiopyran-3-4-dicarboximide/chitosan (TXICh) structure was characterized by 1D (1H and 13C) and 2D (1H 1H COSY, 1H 13C HSQC and 1H 13C HMBC) NMR experiments. TXICh showed absorption in a wide region of the visible, with bands at 385, 450 and 540 nm. Fluorescence measurements showed three emitting states with lifetimes of 3, 0.612 and 0.021 ns. Transient lifetimes of the same magnitude were found for TXICh by femtosecond time-resolved pump-probe transient absorption spectroscopy. TXICh triplet formation was observed by flash photolysis. This excited state is responsible for producing radicals, which initiate photopolymerization. The efficiency of TXICh as a biopolymeric photoinitiator was checked by photopolymerization kinetics of TEGDMA using photocalorimetry (photo-DSC). The ability and efficiency of TXICh to act as photoinitiator radical in different wavelengths was confirmed.

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