The photoinitiator of bifunctional α-hydroxy ketone with long-wavelength in photopolymerization under UV-LEDs

α-hydroxy ketone photoinitiators have been widely used in the photopolymerization industry, such as coating, ink and adhesive, for they have high initiating activity, good thermal stability, and yellowing resistance. However, few works have been reported in developing α-hydroxy ketone photoinitiators that match the absorption of long wavelength LEDs. In this work, a new bifunctional α-hydroxy ketone photoinitiator, (1,4-phenylene) bis (4-hydroxy-4-methylpent-1-en-3-one) (B-HMP), was synthesized and characterized. B-HMP exhibited excellent absorption among the wavelength of 300– 400 nm due to the introduction of unsaturated double bonds which could be employed to match 365/405 nm LEDs. From the results of electron spin resonance spin-trapping (EPR-ST) and steady-state photolysis investigations, the mechanism of the generation of radicals of B-HMP may be via not only the cleavage of CC bonds, but also intermolecular hydrogen abstraction. The efficiency of photopolymerization of B-HMP and triethanolamine (TEOA) was better than those of B-HMP alone because of the synergistic effect. Furthermore, the B-HMP/TEOA had a significantly yellowing resistance property.