The use of external stimuli, such as pH, pressure, and light, as tools in organic synthesis has vastly expanded the scope of accessible materials in polymer chemistry. Specifically, light serves as an inexpensive, abundant, and adaptable stimulus to induce chain growth. With the advent of photocontrol, chemists are now able to reversibly commence and halt chain growth. Until recently, this level of control had been mainly confined to radical processes. Only over the last few years, photocontrol has been expanded to polymerizations with cationic intermediates. Employing photocatalysts which are highly oxidizing in their excited state allowed us to successfully develop a novel cationic photocontrolled polymerization of vinyl ethers. The method exhibits living characteristics, good chain-end fidelity, and spatial and temporal control over chain growth – mediated by light. Utilizing a variety of analytical methods, such as UV-Vis spectroscopy, electron-spin resonance, and time-resolved fluorescence spectroscopy, enabled us to elucidate the mechanism of our photocontrolled cationic polymerization. Additionally, we found a strong link between the electrochemical properties of the photocatalysts and the degree of temporal control we can achieve. This allowed us to determine multiple cationic iridium complexes as superior photocatalysts with improved on-off behavior.<sup> </sup>Furthermore, we successfully coupled our photocontrolled cationic polymerization with photocontrolled radical RAFT-polymerization to synthesize copolymers of vinyl ethers and acrylates. By modulating the photocatalyst ratio, we were able to tune the block length of our copolymers and simply switch between polymerization mechanisms. Importantly, we demonstrate that light can not only start and stop polymerization, but selectively induce one polymerization mechanism over the other and thus serves as a very powerful external stimulus in polymer synthesis.

Photocontrolled cationic polymerization of vinyl ethers and its application in copolymer synthesis

256th National Meeting (2018)

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