Effect of Terminal Alkyl Chains for Free Radical Photopolymerization Based on Triphenylamine Oxime Ester Visible‐Light Absorbing Type I Photoinitiators

Abstract

In order to investigate the photopolymerization properties of the alkyl chain length dependence Type I photoinitiators, in this study, a series of visible‐light‐absorbing triphenylamine oxime esters (Peko‐A‐D, and reference TP‐1M) containing various alkyl chain length in the periphery were synthesized. That is, an alkane segment contains isopropyl for Peko‐A, butyl for Peko‐B, undecane for Peko‐C, pentadecane for Peko‐D and methyl for TP‐1M, respectively. Except for Peko‐D, all of them have good organo‐solubility and can dissolve in testing monomer (trimethylolpropane triacrylate, TMPTA). All the oxime esters give from near UV to visible‐light absorption regions with maximum absorption peaks at around 360 nm and show rather red‐shifted compared to the commercial OXE‐01 compound. Accordingly, the photochemical reaction behavior was studied by cyclic voltammograms (CV), electron spin resonance (ESR) and steady‐state photolysis. In addition, the oxime esters based photoinitiating systems are studied through photo‐DSC experiment based on various light exposure wavelengths (UV lamp, LED@365 nm and LED@405 nm). Under different light source, the penetration affects the final double conversion efficiencies. As a result, all the oxime esters‐based formulation shows better double conversion efficiencies upon LED@405 nm as an irradiation source. Finally, the new oxime ester photoinitiating system was capable applied in direct laser write to generate 3D patterns using a laser diode @405 nm.

Recent advances on phenothiazine-based oxime esters as visible light photoinitiators of polymerization

“…[53] In order to get a sufficient absorption in the visible range, chromophores different from those used in benchmark photoinitiators have to be used or structurally modified in order to improve their absorptions in the visible range. Thus, anthraquinone, [62] coumarins, [55,[63][64][65][66] carbazole, [67][68][69][70][71][72][73][74][75] carbazole-fused coumarins, [14,76,77] pyrene, [78] anthracene, [78] naphthalene, [79] triphenylamine, [80][81][82][83][84] thioxanthone, [85] phenylthioether thiophene, [86,87] bis-chalcones, [88] fluorophenyl derivatives, [89] stilbene derivatives, [90] thiophene derivatives, [91] naphthoquinones, [92] naphthalimides [93] and chalcones [94] have notably been examined as chromophores for the design of oxime esters. Among potential structures, phenothiazine has recently been used for the design of Type II and Type I photoinitiators.…”