Facile Access to Well-Controlled Backbone-Degradable Multiblock and Statistical Copolymers from Living ROMP

Traditional ring-opening metathesis polymerization (ROMP) reactions exhibit wide functional group compatibility and precise con-trol over polymer architectures, albeit with nondegradable backbones. Recent progress has resulted in a series of degradable ROMP products with diverse cleavable functional groups that are derived from the corresponding monomers. However, the major-ity of the monomers display moderate to low ring strain, which restricts their living polymerization reactivity. In this study, a novel category of readily available 7-oxa-2,3-diazanorbornenes (ODAN) is presented, which exhibits the highest ring-strain (22.8 kcal/mol) compared to existing degradable ROMP monomers. This trait endows ODAN with the ability to perform living polymer-ization reactions, generating narrowly dispersed homopolymers, block copolymers, and statistical copolymers with various cyclic olefin comonomers, thereby enabling precise control over the distribution of degradable functional groups. Additionally, the re-sultant polymers comprise directly connected allyl hemiaminal ether and urethane units, which are hydrolyzed at controllable rates. Thus, these well-defined, structure-tunable, and backbone-degradable ROMP polymers are successfully applied as nano-etching materials and biodegradable drug delivery vehicles.