Novel benzophenone derivatives for low intensity visible light polymerization and multi-color 3D printing

Abstract

Four novel benzophenone photoinitiators were synthesized by one-step reaction, including (4-(dimethylamino)phenyl)(10-ethyl-10H-phenothiazin-3-yl)methanone (PEPM), (4-(dimethylamino)phenyl)(10-phenyl-10H-phenothiazin-3-yl)methanone (PPPM), (10-allyl-10H-phenothiazin-3-yl)(4-(dimethylamino)phenyl)methanone (PAPM) and (4-(dimethylamino)phenyl)(10-(hex-5-en-1-yl)-10H-phenothiazin-3-yl)methanone (PHPM). Compared with benzophenone (BP), the absorption spectra of PIs are red-shifted to the visible light range, with a high molar absorption coefficient and wide absorption range from 365 nm to 475 nm. Surprisingly, under the irradiation of low intensity LED@405 nm (5 mW/cm2) and LED@440 nm (5 mW/cm2), PIs can initiate free radical polymerization and undergo rapid polymerization of PEGDA 400. Among them, the double bond conversion rate (DC) of PPPM reaches a stable value (98 %) within 20 s, which is much higher than that of BP (65 %). In addition, the curing depth of PPPM reaches 8.1 cm under the irradiation of LED@440 nm. Besides, PPPM can still perform multi-color 3D printing with 3 s/slice after adding different color (black, red, blue and yellow) dyes. At the same time, we explored the photopolymerization mechanism of the photoinitiator through photodegradation and ESR tests.