Formation of a Polypseudorotaxane via Self-Assembly of γ-Cyclodextrin with Poly(N-isopropylacrylamide)

A polypseudorotaxane (PPR) comprising ?-cyclodextrin (?-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 a-, beta-, and ?-CDs. It can fit into the cavity of ?-CD to give rise to a PPR, but cannot pass through a-CD and beta-CD under the same conditions. The ratio of the number of ?-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 ?-CD molecule. This finding opens new avenues to PPR-based supramolecular polymers to be used as solid, stimuli-responsive materials.