Benzophenone-Functionalized Oligo(Amido Amine)/Iodonium Salt Systems as Visible Light Photoinitiators

Two water soluble oligomeric photoinitiators (OAA-B and OAA-BP) were synthesized by first preparing an oligo(amido amine) (OAA) via aza-Michael addition reaction of N,N'-methylene bisacrylamide and 1,4-diaminobutane, then carrying out another aza-Michael addition reaction between OAA and 4-benzoylphenyl acrylate for OAA-B and also diethyl vinylphosphonate for OAA-BP. Photopolymerization kinetics of 2-hydroxyethyl methacrylate (HEMA) and HEMA: poly(ethylene glycol) diacrylate (PEGDA, M-n = 575) mixture initiated by these photoinitiators were monitored by real-time FTIR spectrophotometer and photo-DSC. These photoinitiators together with bis-(4-tert-butylphenyl)-iodonium hexafluorophosphate (Iod) have high polymerization efficiencies under UV and unexpectedly visible light exposure. The efficiency of the photoinitiators is based on two separate mechanisms, oxidative interaction between benzophenone group and Iod and charge transfer complex (CTC) formation between Iod and amines in OAA; verified by absorption, steady state photolysis, electron spin resonance and laser flash photolysis. The CTC formation mechanism was also studied by molecular modeling studies; and both mechanisms generating aryl radicals.