Confinement of polymers in nano-spaces can induce unique molecular dynamics and properties. Here we show molecular weight fractionation by the confinement of single polymer chains of poly(ethylene oxide) (PEO) in the one-dimensional (1D) channels of crystalline pillar[5]arene. Pillar[5]arene crystals are activated by heating under reduced pressure. The activated crystals are immersed in melted PEO, causing the crystals to selectively take up PEO with high mass fraction. The high mass fractionation is caused by the greater number of attractive CH/π interactions between PEO C-H groups and the π-electron-rich 1D channel of the pillar[5]arene with increasing PEO chain length. The molecular motion of the confined PEO (PEO chain thickness of ~3.7 Å) in the 1D channel of pillar[5]arenes (diameter of ~4.7 Å) is highly restricted compared with that of neat PEO.

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.

Polyrotaxanes constructed from hydrogen‐bonding pillar[5]arene rings and poly(ethylene oxide) chains were synthesized. A polyrotaxane with a high‐molecular‐weight poly(ethylene oxide) chain showed temperature‐dependent shape memory properties, because of the topological confinement and cross‐linked hydrogen bonds. The hydrogen bond networks constructed from pillar[5]arene rings and poly(ethylene oxide) chains are illustrated as music notes and staff notation, respectively. More information can be found in the Full Paper by T. Ogoshi et al. on page 6435.

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. Specifically, 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 confinement and cross-linking by hydrogen bonds.

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