Thermally Responsive Poly(ethylene oxide)‐Based Polyrotaxanes Bearing Hydrogen‐Bonding Pillar[5]arene Rings**

Abstract

Poly(ethylene oxide)s (PEOs) are useful polymers with good water solubility, biological compatibility, and commercial availability. In this study, PEOs with various end groups were threaded into pillar[5]arene rings in a mixture of water and methanol to afford pseudopolyrotaxanes. Multiple hydrogen bonds between the pillar[5]arene rings and hydrophobic-hydrophilic interactions between the ethylene groups of the PEOs and the hydrophobic pillar[5]arenes are the driving forces to form the pseudopolyrotaxane structure. Corresponding polyrotaxanes were also constructed by capping COOH-terminated pseudopolyrotaxanes with bulky amines, in which multiple hydrogen bonds involving the pillar[5]arene OH groups were critically important to prevent de-threading. The number of threaded ring components could be rationally controlled in these materials, providing a simple and versatile method to tune the mechanical and thermal properties. Speci cally, a polyrotaxane with a high-molecular-weight axle became elastic upon heating above the melting point of PEOs and exhibited temperature-dependent shape memory property, because of the topological con nement and cross-linking by hydrogen bonds.

Mechanically interlocked polymers based on rotaxanes

“…114 Other non-ionic polymers can be used as the axles of pillar[ n ]arenes-based polyrotaxanes, such as poly( ε -caprolactone) (PCL) 115 and poly(ethylene oxide) (PEO). 116 Furthermore, adamantane units are commonly used as the end-capped groups. We believe that more novel topological materials can be designed based on the recognition property and further functionalization of pillar[ n ]arenes.…”

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

“…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][77][78][79][80][81][82] The intermittent energy ratchet operation mode afforded by successive threading and dethreading processes in molecular pumps inspired Stoddart and colleagues to envision the concept of active mechanisorption by using a pioneering approach to incorporate rotaxane-based molecular pumps into MOF nanosheets. In this example, a series of pumping cassettes (MPCG) were embedded into the surface of MOF nanosheets, promoting the out-of-equilibrium integration of macrocycles on their collecting threads.…”

“…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] …”

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes

“…Furthermore, owing to the multiple hydrogen bonds inside, PR3 exhibited thermoplastic behaviour and shape memory properties without further functionalization or crosslinking. 217 Pseudopolyrotaxanes between PEOs and perethylated pillar [5]arene were prepared through crystalline-state complexation (Fig. 48).…”

“…Furthermore, owing to the multiple hydrogen bonds inside, PR3 exhibited thermoplastic behaviour and shape memory properties without further functionalization or crosslinking. 217…”