Formation Mechanism of Polycatenane by Direct Catenation

Polycatenanes, a novel class of polymers consisting of interlocked macrocyclic monomers, have attracted significant attention. However, the formation mechanism of polycatenanes through direct catenation remains poorly understood. Herein we explore the structural diversity and unique chain termination mechanism inherent to polycatenanes. Unlike conventional linear polymers, a linear polycatenane exhibits a variety of topological configurations, with chain growth terminated upon the formation of completely interwoven structures. This intrinsic termination, characterized by the probability q, necessitates a modification of the classical Carothers equation to accurately determine the number-average degree of polymerization (DPn). Using importance sampling-based Monte Carlo algorithm, we have investigated the influence of interaction strength ϵ between monomers and cavity size l(σ) of a monomer on the termination probability q. Our findings reveal that stronger intermolecular interactions increase q, while larger cavity size promotes higher-order catenation with a lower q. To achieve polycatenanes with higher DPn, we propose two strategies—employing directional interactions and introducing steric hindrance—to prevent the formation of completely interwoven structures. These approaches, enable the synthesis of polycatenanes with sustained reactivity, offering new pathways for the design of polymer with sophisticated topologies and configurations.