Norbornenyl-based amphiphilic ABA-triblock azobenzene copolymers: Synthesis, photoresponsive and self-assembly properties

A series of well-defined ABA-triblock copolymers P(NB-P(t)BA)(x)-b-P(NB-PFP)(y)-b-P(NB-P(t)BA)(x) were synthesized by living ring-opening metathesis polymerization (ROMP) of norbornenyl-poly(tert-butyl acrylate) (NB-P(t)BA), norbomenyl-pentafluomphenyl (NB-PFP) and NB-P(t)RA in a sequential manner by the use of Grubbs' third generation catalyst (G(3)). The corresponding amphiphilic ABA-triblock azobenzene copolymers P(NB-PAA)(x)-b-P (NB-Azo)(y)-b-P(NB-PAA)(x) were obtained in high yields after subsequent post-polymerization modifications, including the reaction of active esters with amine-functionalized azobenzene to introduce the azobenzene unit, and the hydrolysis reaction to remove the tert-butyl groups. Under alternating UV and visible light illumination, the light response behaviors of the polymers were demonstrated by UV-Vis spectroscopy, and the reversible changes were observed as a result of the reversible trans-cis photoisomerization of azobenzene mesogens. These amphiphilic copolymers can also spontaneously self-assemble into spherical nanoparticles in an aqueous medium, and the hydrodynamic diameter increases as the hydrophobic NB-Azo content increases.