N-acetyl-4-nitro-1-naphthylamine as sensitizer of N, N-dimethylaniline for photoinitiated radical polymerization

Abstract

Photophysical, photochemical behaviour of N-acetyl-4-nitro-1-napthylamine (ANNA) in the presence of N, N-dimethylaniline (DMA) was analyzed to establish the influence of the nature of this nitroaromatic initiator on the photosensitized generation of free radicals during photoinitiated polymerization of lauryl acrylate (LA) monomer. Steady-state (365 nm) photolysis was studied providing experimental evidence of a photosensitization process of DMA through excitation energy transfer from ANNA. The dependence of the consumption rate of both reactants on the irradiation time reveals that up to 87 molecules of DMA are consumed for each ANNA molecule photoreduced in spite of the low photoreduction quantum yield of ANNA induced by DMA. The efficiency of the ANNA/DMA system as photoinitiator was studied by following the polymerization kinetics of LA monomer by Differential Scanning Photo-Calorimetry (Photo-DSC). The photosensitization of DMA, working concurrently to the photoreduction reaction, induces a polymerization efficiency up to 5 times higher than that reached with other nitroaromatic initiators.