Synthetic Strategy for Mechanically Interlocked Cyclic Polymers via the Ring-Expansion Polymerization of Macrocycles with a Bis(hindered amino)disulfide Linker

Abstract

Mechanically interlocked polymers that contain rotaxane and catenane structures have attracted much attention on account of their unique properties arising from the restricted mobility of their interlocked structure and their robustness which are comparable to those of covalent bonds. Among these polymers, mechanically interlocked cyclic polymers (MICPs) exhibit great potential as a novel type of polymer with a large movable area of the interlocked structure. However, synthetic routes to MICPs are not well developed, and it is still challenging to create MICPs. The present study has resulted in an effective method for the synthesis of MICPs from the combination of the ring-expansion polymerization (REP) of cyclic disulfide monomers with supramolecular interactions. Macrocyclic monomers (MMs) that consist of a bis(hindered amino)disulfide (BiTEMPS) linker and a supramolecular moiety, such as naphthalenediimide (NDI) and dialkoxynaphthalene (DAN), capable of forming a strong 1/1 charge-transfer complex, were synthesized as the monomers for the subsequent REP. These MMs were used in a heat-induced REP in the bulk state, which led to their swift polymerization via an intermolecular exchange reaction of BiTEMPS. The change in mechanical properties during the polymerization was monitored by rheological measurements of the increase of the storage modulus, G′. Importantly, the bulk copolymerization of the MMs containing NDI and DAN increased the hydrodynamic volume of the resulting copolymers, which is due to the spatial entanglement of the polymer chains. The change in the physical properties of the resulting polymers stands in sharp contrast to that observed in polymers with a linear topology made from the same monomers, thus supporting the formation of MICPs. The results provide guidelines for the successful design of MICPs, that is, a combination of the dynamic nature of the MMs and supramolecular interactions. Given that the present method is highly versatile, it can be expected to be applicable to various molecular skeletons and supramolecular systems.

Polycatenanes: synthesis, characterization, and physical understanding

“…81 Recent efforts have detailed the ring expansion polymerization of cyclic disulfides, bearing an additional supramolecular moiety on each ring to make a charge transfer complex between rings, thus promoting catenation. 82 The synergy of supramolecular interactions coupled with reversible bonds seems an attractive methodology for the formation of these materials, particularly in systems where the supramolecular interactions, and thus material properties can be modulated by external stimuli.…”

The Role of Dethreading Process in Pseudorotaxanes and Rotaxanes towards Advanced Applications: Recent Examples

“…Indeed, this strategy has allowed to transfer the inherent dynamic of the counterparts of rotaxanes from solution to the solid state, leading to macroscopic implementations. In this scenario, metal‐organic frameworks (MOFs) and polymers have turned out to be ideal and tailorable scaffolds in order to integrate rotaxanated compounds in solid‐state ordered materials [76–82] …”

Ring-chain equilibria of dynamic macrocycles with a bis(hindered amino)disulfide linker

“…We previously developed a ROP system utilizing the dynamic covalent chemistry [28][29][30] of bis(2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS). [31][32][33][34][35] The BiTEMPS structure can exchange its disulfide bonds above 80 °C via the generation of relatively stable sulfide radicals (Scheme 1a), providing a dynamic polymer system. [36][37][38][39] Macrocyclic monomers (MMs) with desired structures and one BiTEMPS unit can be synthesized via selective and efficient cyclodepolymerization 31 of linear polymers containing BiTEMPS units in their repeating units, i.e., ring-chain equilibria with low concentrations.…”

“…, ring-chain equilibria with low concentrations. Isolated MMs can be polymerized by heating in highly concentrated conditions, whereupon they are converted to cyclic polymers (CPs), 32 mechanically interlocked CPs (MICPs), 33 or end-defined LPs 34 (Scheme 1b). The resulting polymers may be recycled by heating without any catalysts because they contain a dynamic amino disulfide bond in their repeating units.…”