Effects of hydroxypropyl cyclodextrins on phase transition temperatures of poly(n-isopropylacrylamide) and poly(n-isopropylacrylamide-co-octadecylacrylate)

摘要

The phase transition temperatures (PTTs) of poly(N-isopropylacrylamide) (PNIPAM) decreased with increasing concentration of hydroxypropyl cyclodextrins (HPCDs), possibly due to the ability of the cyclodextrin (CD) cavity to facilitate the hydrophobic interact of PNIPAM chains. The capability to decrease the PTT was in the order of HPcCD>HPbCD>HPaCD. However, the PTTs of hydrophobically modified PNIPAM (HmPNIPAM), poly(N-isopropylacrylamideco- octadecylacrylate), increased with the concentration of HPCDs in a lower concentration range (0-4.0% or 0-8.0%), but it decreased with the concentration in a higher range (4.0-32.0% or 8.0-32.0%). In the lower HPCD concentration range, the interaction of the CD cavity with ODA residues may be prevailing and it will interfere with the hydrophobic interaction of octadecylacrylate residue, leading to an increase in the PTT. In the higher HPCD concentration range, the interaction of the CD cavity with PNIPAM segments may be dominant and it would promote the hydrophobic interaction of the segments, resulting in a decrease in the PTT.