Fast and Reversible Photoresponsive Self-Assembly Behavior of Rosin-Based Amphiphilic Polymers

Designing stimulus-responsive amphiphilic polymers with a fast photoresponsive self-assembly behavior remains a challenge. Two series of rosin-terminated and azobenzene-terminated amphiphilic polymers (PAMn and PMAn) with fast and reversible photoresponsive properties were prepared using rosin-based azobenzene groups and polyethylene glycol, respectively. Under 5-10 s of UV irradiation, the polymers showed trans-to-cis isomerization and reached a photosteady state. For the PAMn polymer, the absorbance of the absorption peak at 325 nm recovered to more than 95% of the initial value under visible light for 5- 10 s, whereas that of the PMAn polymer recovered completely. Notably, the PAMn and PMAn polymers initially self-assembled to vesicles or spherical micelles, and various morphological changes were achieved by manipulating UV irradiation time, with the initial morphology again recovered under dark conditions or visible-light irradiation. Remarkably, vesicles of the PAM34 and PMA34 polymers presented an intermediate open-vesicle state before being completely deformed under UV irradiation because of the existence of a pi-pi interaction. Finally, the ability of PAM34 and PMA34 polymer vesicles to perform the controlled release and reversible loading of a fluorescent probe was evaluated.