Triggering the Thermosensitive Properties of Hydrophobically Modified Poly(<i>N</i>‐isopropylacrylamide) by Complexation with Cyclodextrin Polymers

Abstract

Abstract Summary: Hydrophobically modified poly( N ‐isopropylacrylamide) (PNIPAM) containing either an adamantyl or a dodecyl group were prepared and characterized. Self‐association in aqueous solutions was evidenced by fluorescence measurements using pyrene as a probe. The lower critical solution temperatures (LCST) were determined from cloud point measurements. They strongly depended on the hydrophobic group and the substitution level. The association between hydrophobically modified PNIPAM and β ‐cyclodextrin (monomers and polymers) was investigated by cloud point and viscosity measurements. The presence of β ‐cyclodextrin monomers generally shifted the LCST to a higher temperature, the complexation increasing the solubility of PNIPAM chains. β ‐Cyclodextrin polymers mixed with hydrophobically modified PNIPAM generated supramolecular assemblies. This was evidenced by viscosity measurements of the mixtures at temperatures lower than the LCST. Moreover, depending on the substitution level of the PNIPAM, the LCST was increased (1% hydrophobic groups) or decreased (4% hydrophobic groups) by more than 10 °C upon β ‐cyclodextrin polymer addition. Transmission variations of different mixtures of PNIPAM‐C12 with cyclodextrin compounds vs temperature. image Transmission variations of different mixtures of PNIPAM‐C12 with cyclodextrin compounds vs temperature.