Mechanistic Insight into the Photocontrolled Cationic Polymerization of Vinyl Ethers,Journal of the American Chemical Society

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Mechanistic Insight into the Photocontrolled Cationic Polymerization of Vinyl Ethers
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2017-10-18 00:00:00 , DOI: 10.1021/jacs.7b09539
Quentin Michaudel ₁ , Timothée Chauviré ₁ , Veronika Kottisch ₁ , Michael J. Supej ₁ , Katherine J. Stawiasz ₁ , Luxi Shen ₁ , Warren R. Zipfel ₁ , Héctor D. Abruña ₁ , Jack H. Freed ₁ , Brett P. Fors ₁

Affiliation

The mechanism of the recently reported photocontrolled cationic polymerization of vinyl ethers was investigated using a variety of catalysts and chain-transfer agents (CTAs) as well as diverse spectroscopic and electrochemical analytical techniques. Our study revealed a complex activation step characterized by one-electron oxidation of the CTA. This oxidation is followed by mesolytic cleavage of the resulting radical cation species, which leads to the generation of a reactive cation—this species initiates the polymerization of the vinyl ether monomer—and a dithiocarbamate radical that is likely in equilibrium with the corresponding thiuram disulfide dimer. Reversible addition–fragmentation type degenerative chain transfer contributes to the narrow dispersities and control over chain growth observed under these conditions. Finally, the deactivation step is contingent upon the oxidation of the reduced photocatalyst by the dithiocarbamate radical concomitant with the production of a dithiocarbamate anion that caps the polymer chain end. The fine-tuning of the electronic properties and redox potentials of the photocatalyst in both the excited and the ground states is necessary to obtain a photocontrolled system rather than simply a photoinitiated system. The elucidation of the elementary steps of this process will aid the design of new catalytic systems and their real-world applications.

中文翻译：

乙烯基醚的光控阳离子聚合的机理研究

使用多种催化剂和链转移剂（CTA）以及各种光谱学和电化学分析技术，研究了最近报道的乙烯基醚的光控阳离子聚合反应的机理。我们的研究揭示了一个复杂的活化步骤，其特征在于CTA的单电子氧化。这种氧化反应之后，是对所得自由基阳离子物质的介观裂解，这导致了反应性阳离子的产生（该物种引发了乙烯基醚单体的聚合），以及可能与相应的秋兰姆二硫化二聚体处于平衡状态的二硫代氨基甲酸酯基团。。在这些条件下观察到，可逆的加成-断裂型简并链转移导致了窄的分散性和对链增长的控制。最后，失活步骤取决于二硫代氨基甲酸酯基对还原的光催化剂的氧化作用，并伴随产生封盖聚合物链端的二硫代氨基甲酸酯阴离子。光催化剂在激发态和基态下的电子性质和氧化还原电势的微调对于获得光控系统而不是光引发系统都是必需的。阐明该过程的基本步骤将有助于设计新的催化体系及其实际应用。光催化剂在激发态和基态下的电子性质和氧化还原电势的微调对于获得光控系统而不是光引发系统都是必需的。阐明该过程的基本步骤将有助于设计新的催化体系及其实际应用。光催化剂在激发态和基态下的电子性质和氧化还原电势的微调对于获得光控系统而不是光引发系统都是必需的。阐明该过程的基本步骤将有助于设计新的催化体系及其实际应用。

更新日期：2017-10-19

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