Formation Mechanism of Polycatenane by Direct Catenation

Polycatenanes, a novel class of polymers consisting of interlocked macrocyclic monomers, have attracted significant attention. However, the mechanism of formation 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 (DP_n). Using the importance of sampling-based Monte Carlo algorithms, we have investigated the influence of the interaction strength ϵ between monomers and the cavity size l(σ) of a monomer on the termination probability q. Our findings reveal that stronger intermolecular interactions increase q, while a larger cavity size promotes higher-order catenation with a lower q. To achieve polycatenanes with higher DP_n, 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 polymers with sophisticated topologies and configurations.