LED and visible light-induced metal free ATRP using reducible dyes in the presence of amines

Solar energy is the basis of all changes in nature. Most typical chemical reactions such as photosynthesis is sum of a series of step reactions using solar energy. Such naturally occuring reactions give inspiration to the chemists to apply photochemical strategies on varios chemical synthesis. Photochemical synthesis holds significant advantages over the traditional routes such as thermal and spatial control and low-energy requirements. More recently, the choice of sustainable, low-energy demanding processes compare to the conventional strategies become dominant which seems to be reasonable due to the changing financial and ecological patterns of the world. The year 2015 was declared to be the "International Year of Light" by UNESCO, emphasizing the indispensable quality of light in scientific, cultural, medical and social platforms. Applications of the light energy to the polimer science spread to a broad scale resulting in an increasing number and quality of the efforts on the topic. However, the development and utilization of environmentally friendly, reusable and low-energy using light-induced processes is still below satisfactory levels from the point of view of both academic and industrial demands. In addition, synthesis of macromolecular structures with well-defined structures and functional groups, and controlled molecular weights has become an important research field for polymer scientists. Among the controlled radical polimerization methods, atom transfer radical polymerization (ATRP) is the most-widely used method as it has high tolerance towards many functional groups present in the initiator and monomer structure and is applicable to a wide range of monomers. The major drawback associated with the ATRP process is the requirement of the low oxidation state copper halide catalytsts, which are hard to remove from the polymers obtained. The residual inorganic materials in these polymers prevent the application of these materials espacially in bioapplications. In addition, these are thermal processes and application of photochemical strategies to overcome these advantages are insufficient. Thus, additional innovative research is required due to the insufficiency of adaptation of light into the present technologies and the existence of drawbacks in the proposed strategies. In the preparation of macromolecular structures, linear polymer and network structured polymers, based on epoxy systems, synthesis deserve special attention. In this respect, photochemical methodologies are widely used as they provide low-energy requirements and simpler experimentation procedures. Recently, it has been demonstrated that some controlled polymerization techniques can be performed in the absence of inorganic catalysts by the help of light energy. Moreover, it has been also shown that the industrially applied epoxy curing can be achieved by photochemical procedures. Limited number of the existing technologies in this field proves that the topic is open to new developments and innovations. A new photoinitiating system involving electron acceptor dyes, namely eosin Y and erythrosin B in conjunction with alkyl halides and amines for photo-induced ATRP of (meth)acrylates and vinyl monomers in the absence of inorganic catalysts is reported. The polymerizations could be efficiently activated by the photomediated redox processes producing polymers with controlled chain end functionality and narrow molecular weight distribution. The dye/amine system was shown to be efficient under various colors of LED and industrially available visible light irradiation. The livingness nature of the polymerization was proved by GC analyses and the irradiation dependency of polymerization was confirmed by light on/off experiments.