Hydrophilic-hydrophobic phase transition of photoresponsive linear and macrocyclic poly(2-isopropyl-2-oxazoline)s

A series of macrocyclic and linear poly(2-isopropyl oxazoline)s containing a photoresponsive azobenzene moiety (Az-PiPOxs) were synthesized by Cu(i)-catalyzed cycloaddition reaction between azide-functionalized azobenzene and alkyne-bearing poly(2-isopropyl oxazoline)s. Upon temperature elevation, both macrocyclic and linear Az-PiPOx exhibited a sharp hydrophilic-to-hydrophobic phase transition: the initially clear solution became turbid at specific temperatures. The photoisomerization of the azobenzene moiety resulted in the large change of the thermal transition temperature of the polymers. cis isomers exhibited a higher thermal transition temperature than trans isomers. Thus, the phase transition can be controlled by 365 and 254 nm UV irradiation.