Pyrrolidone based one-component photoinitiator for improving the storage stability of photocurable materials to sunlight via two beams of light excitation

Abstract

The use of a light emitting diode (LED) light photoinitiator endows photopolymerization with comfortable irradiation conditions since LED owns advantages such as longer lifespan and no ozone generation. However, photoinitiator for LED irradiation (LED photoinitiator) was much more easily excited by outdoor sunlight compared to UV photoinitiator. As a result, photocurable materials containing LED photoinitiator exhibits poor storage stability to sunlight because sunlight in the visible light region exhibits wider absorption wavelength and higher penetrating ability than UV light. In this research, pyrrolidone one-component LED photoinitiator with chalcone structure(E)-1-(4-(dimethylamino)phenyl)-3-(1H-pyrrol-2-yl)prop-2-en-1-one(E-DNPO) was synthesized, and its cis isomer Z-DNPO was also obtained from the photoequilibrium state of E/Z-DNPO. All the characterization including photolysis experiments, real-time 1H NMR spectra and photopolymerization kinetics verified that cis isomer Z-DNPO cannot be stimulated by sunlight as intramolecular hydrogen bonding N-H···O = C hinders the carbonyl group from capturing hydrogen via donors to launch the polymerization. However, Z-DNPO can recover its initiating ability to polymerize different monomers upon LED@365 nm as it transforms into E-DNPO under the irradiation of LED@465 nm beforehand. This initiating system with controllable photoactivity via two beams of light excitation, directly improving the storage stability of photocurable materials, thereby making the uses, preparation and application of photocurable materials more convenient.