Abstract
Poly(ethylene oxide)s (PEOs) are useful polymers with good water solubility, biological compatibility, and commercial availability. PEOs with various end groups were threaded into pillar[5]arene rings in a mixture of water and methanol to afford pseudopolyrotaxanes. 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 dethreading. 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 crosslinked hydrogen bonds.
Highlights
Topological supramolecules are materials assembled from geometrically confined or interlocked components instead of rigid covalent bond frameworks
P5OH was dissolved in a mixture of water and methanol [1/1 (v/v)], to which was added a solution of OH-terminated Poly(ethylene oxide)s (PEOs) PEO2k-OH in the same solvent system
We have developed versatile methods for the preparation of pseudopolyrotaxanes assembled from PEOs and P5OH, by employing a mixed solvent system of water and methanol
Summary
Topological supramolecules are materials assembled from geometrically confined or interlocked components instead of rigid covalent bond frameworks. The formation of pseudopolyrotaxane and polyrotaxane with PEO axles was accomplished by Harada and co-workers in the 1990s, using α-cyclodextrin (α-CD)[15−17] as the ring components (α-CDPEO-OH and α-CDPEO-NHAr in Fig. 1).[8−11,18,19] In these examples, the pseudopolyrotaxanes were collected as precipitates by mixing aqueous solution of α-CD and that of PEOs. Intermolecular hydrogen bonds between the α-CDs and hydrophobic–hydrophilic interactions between the hydrophobic ethylene groups of the PEOs and αCD cavity are the driving forces to form the pseudopolyrotaxane structure. Considering the great success of supramolecular polymer materials composed of PEOs and cyclodextrins,[24−30] alternative cyclic hosts for PEO axles are highly desirable for the further development of PEO-based hydrogels and other functional materials
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