Aza-Michael Addition-Fragmentation Ring-Opening Polymerization

Cleaving the C(sp³)-N bonds in unstrained cyclic monomers for ring-opening polymerization remains a formidable challenge in polymer chemistry. Here, we report a novel strategy that integrates the cascade aza-Michael/retro-aza Michael reaction with a chain growth polymerization mechanism. For the first time, this approach cleaves the C(sp³)-N bond in less-strained cyclic monomers under ambient conditions, yielding cinnamate-containing polyamines with controlled molecular weight, narrow dispersity, and unexpected cis-stereoselectivity. A linear relationship between the number-average molecular weight and the conversion, high chain-end fidelity, and efficient chain extension proved excellent control over the polymerization process. In addition, density functional theory calculations were conducted to clarify the origin of the observed stereoselectivity. The versatility of this polymerization was further demonstrated through the copolymerization with aziridine monomers and the synthesis of sequence-controlled polymers. This protocol provides a new C-N cleavage pattern for ring-opening polymerization and would lead to a more useful synthetic pathway to polymers with main-chain functionalities.