Spiro-Confined Brønsted Acid Catalyst for Stereoselective Cationic Polymerization of Vinyl Ethers

The polymerization-targeted design of catalysts is critical to the development of high-performance polymer materials. Herein, we introduced a class of strong Brønsted acid catalysts, spiro N, N ′ - bis(triflyl)phosphoramidimidates (SPADIs), which possess a spiro-confinement and show high efficiency and high stereoselectivity in the cationic polymerization of vinyl ethers. Particularly, SPADIs exhibited good compatibility with a variety of degenerative chain transfer (DT) agents, thus enabling the synthesis of isotactic poly(vinyl ether)s with controlled molecular weights, high stereoselectivities (up to 91% m ), and various chain-end functional groups at a low catalyst loading (200 ppm). Single-crystal X-ray analysis and theoretical calculations indicate the SPADI catalyst possesses a deep and confined chiral pocket that could effectively extend the spiro backbone chirality to enhance the face-selectivity, and a preferred formation of the cyclic chelated intermediates in the propagating cationic chain ends. We anticipate that SPADI will find further application in both polymerization and organic reaction development in the future.