Effect of Host–Guest Interactions on the Cloud Points of Neutral Thermosensitive Homopolymers: Poly(N-n-propylmethacrylamide) and Polymers with Similar Structures

We investigated effect of cyclodextrins (CDs) on the cloud point of several thermosensitive polymers that are not ionizable. α-CD increased the cloud point of the poly(N-n-propylmethacrylamide) (PnPMAm) aqueous solution; by contrast, β-CD or γ-CD did not affect the cloud point of the PnPMAm solution. The cloud point of the PnPMAm solution increased gradually with an increase in the concentration of α-CD. Furthermore, we compared the effect of the CDs on the cloud points of four polymers with similar structures. As for poly(N-isopropylacrylamide) (PiPAAm), neither α-CD nor β-CD affected its cloud point. On the basis of the effect of the differently sized CDs on the cloud point of five polymers and the corresponding NOESY NMR data, we inferred that steric hindrance by the main chain of PiPAAm might be responsible for the bulky CD being unable to form a complex with the short isopropyl group.