Temperature sensitive supramolecular self assembly of per-6-PEO-β-cyclodextrin and α,ω-di-(adamantylethyl)poly(N-isopropylacrylamide) in water

Abstract

The host/guest interactions in water of a star polymer consisting of a β-cyclodextrin (β-CD) core bearing six poly(ethylene oxide) arms linked to the C₆ positions of β-CD (β-CD-PEO₇, M_n 5000 g mol⁻¹) and α,ω-di-(adamantylethyl)poly(N-isopropylacrylamide) (Ad-PNIPAM-12K, M_n 12 000 g mol⁻¹) were studied by 1D and 2D ¹H and ¹³C NMR spectroscopy, isothermal calorimetry (ITC), and light scattering (LS). In cold water (T < 26 °C) supramolecular “dumbbell” assemblies, consisting of PNIPAM chains with β-CD/Ad inclusion complexes at each end, formed via β-CD-insertion of the terminal Ads through the β-CD secondary face. Light scattering, microcalorimetry (DSC), and DOSY NMR studies indicated that mixed aqueous solutions of β-CD-PEO₇ and Ad-PNIPAM-12K undergo a reversible heat-induced phase transition at ∼32 °C, accompanied by a release of a fraction of the Ad-bound β-CD-PEO₇ into bulk solution and the formation of aggregated Ad-PNIPAM-12K stabilized by a β-CD-PEO₇ shell.