Precision Synthesis of Polyrotaxanes Using Cascade Metathesis Polymerization

Mechanically interlocked polymers (MIPs), such as polyrotaxanes (PRs) and polycatenanes, represent intriguing synthetic macromolecules distinguished by their unique architectures and topology. These MIPs, characterized by their mechanical bonds and movable component parts, have been extensively utilized across various contemporary fields of chemistry, presenting opportunities for the design of functional materials with enhanced mechanical properties. However, the precision synthesis of MIPs, specifically PRs, with controlled molecular weights and narrow dispersity remains a significant challenge, hindering the progression of well-defined mechanically interlocked materials that exhibit a clear structure-property relationship. Herein, we disclose the controlled chain-growth synthesis of main-chain PRs through cascade metathesis polymerization by employing a catenane-based monomer. A series of PRs with targeted molecular weights, narrow dispersities, and tunable mechanical properties was successfully prepared by adjusting the monomer-to-catalyst feed ratio. The "livingness" of this polymerization was validated through kinetic studies, and the detailed structural characteristics of the synthesized PRs were supported by ¹H NMR spectroscopy and mass spectrometry. Both block and statistical copolymers were produced in a controlled manner through the copolymerization of the catenane-based monomer with other monomers that can undergo ring-opening metathesis polymerization (ROMP), allowing for easy access to PRs featuring different architectures and, most importantly, tunable ring densities. This work significantly advances beyond the majority of previously reported studies concerning the controlled synthesis of PRs, paving the way for the rational design and synthesis of mechanically interlocked materials with desired functionalities.