Photosensitization of N,N-dimethylaniline by N,N-dimethyl-4-nitroaniline as a new bimolecular photoinitiation system for polymerization

Photophysics, photochemical and polymerization activity of N,N-dimethyl-4-n itroaniline (DMNA) alone and in the presence of N,N-dimethylaniline (DMA) a s coinitiator were analyzed to elucidate the influence of the bifunctional character of this compound on the efficiency and mechanism of generating in itiating radicals. The presence of electron donor and acceptor groups in th e same molecule determines the capability of DMNA to initiate the polymeriz ation with higher efficiency and lower initiator consumption as compared wi th conventional bifunctional ketones. Detailed studies of the spectroscopy of both reactants were carried out providing experimental evidence of photo sensitization of DMA through excitation energy transfer from DMNA. The cons umption rate of both reactants reveals that up to 165 molecules of DMA are consumed for each DMNA molecule photoreduced in spite of the low photoreduc tion quantum yield of DMNA induced by DMA. The photosensitization of DMA, w orking concurrently to the photoreduction reaction, enhances the polymeriza tion efficiency as compared with other nitroaromatic initiators.