Formation of a polypseudorotaxane via self-assembly of γ-cyclodextrin with poly(N-isopropylacrylamide)

A polypseudorotaxane (PPR) comprising γ-cyclodextrin (γ-CD) as host molecules and poly(N-isopropylacrylamide) (PNIPAM) as a guest polymer is prepared via self-assembly in aqueous solution. Due to the bulky pendant isopropylamide group, PNIPAM exhibits size-selectivity toward self-assembly with α-, β-, and γ-CDs. It can fit into the cavity of γ-CD to give rise to a PPR, but cannot pass through α-CD and β-CD under the same conditions. The ratio of the number of γ-CD molecules to entrapped NIPAM repeat units is kept at 1:2.2 or 1:2.4, determined by ¹H NMR spectroscopy and TGA analysis, respectively, indicating that there are more than 2 but less than 3 NIPAM repeat units included by one γ-CD molecule. This finding opens new avenues to PPR-based supramolecular polymers to be used as solid, stimuli-responsive materials.