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Abstract
An exploratory investigation into the implementation of visible light mediated reversible deactivation radical polymerization (RDRP) in an aqueous dispersed system is conducted. Visible light mediated Radical Addition-Fragmentation chain Transfer (RAFT) polymerizations provide an energy efficient route to the controlled synthesis of polymers. In contrast to conventional approaches, reactions proceed at room temperature, requiring only exposure to low energy visible wavelengths. Free of harmful radical initiators, this energy efficient synthetic approach can further be enhanced by implementation in an aqueous dispersed system. Doing so affords environmentally-friendly solvent-free conditions that exemplify the green credentials of this technology. However, the turbidity of dispersed polymerization systems is a potential impediment to the successful application of this technology. The use of miniemulsions as a model dispersed system would be a true test to the capabilities of visible light mediated RAFT processes.
Utilizing the Photoinduced Electron/Energy Transfer – Reversible Addition-Fragmentation chain Transfer (PET-RAFT) process, the initial study demonstrated that the implementation of visible light mediated polymerizations in an aqueous dispersed system is indeed feasible and warranted further investigation. Due to the poor solubility of available photocatalysts, the visible light mediated RAFT iniferter process was investigated as an alternative. Operating without the aid of a catalyst, the RAFT iniferter process surprisingly provided faster rates of polymerization. A crucial discovery was made during this work; surface-activity of the RAFT agent induces an exit and ‘frustrated’ re-entry phenomenon that delays nucleation and causes inhibition of the polymerization process.
A simple modification afforded suppression of surface-activity and a corresponding improvement was observed in the polymerization kinetics. The value of this approach was further verified by the superior livingness that was demonstrated in comparison to the surface-active iniferter. These promising results confirm the capability of visible light to mediate polymerization processes despite the turbidity and mark the first steps towards the development of greener polymerization technologies.