Metal-Free Cationic Polymerization of Vinyl Ethers with Strict Temporal Control by Employing an Organophotocatalyst.

By virtue of spatiotemporal control over the chain propagating, visible-light-regulated organocatalytic photoredox cationic polymerization provides an appealing approach for the construction of metal-free, well-defined polymers and materials. However, so far, organic photocatalysts capable of mediated cationic polymerization of vinyl ethers are quite limited, and the photocontrol or efficiency is often eroded due to the difficulty in achieving a good activation-deactivation balance, which is greatly dependent on the redox property of the catalyst. Here, we introduce a new type of organic photocatalysts, bisphosphonium salts, which show high performance in the photoregulated reversible addition-fragmentation chain transfer cationic polymerization of vinyl ethers and allow the synthesis of poly(vinyl ethers) with predictable molecular weights and narrow dispersities at low ppm catalyst loadings under visible light. In particular, the tunable redox potential and excellent stability endow the bisphosphonium salts strict temporal control, thus enabling the metal-free polymerization with a halt in a long dark period.