Double stimuli-responsive azobenzene containing poly(2-oxazoline)s: synthesis, light, and temperature-responsive behavior

Abstract

Amphiphilic polymer materials find a wide range of applications in medicine and diagnostics. Often such polymers are required to be able to adapt their properties depending on the surrounding conditions or external stimuli for targeted application in the body. In this work, we propose an approach for the synthesis of temperature and light-responsive copolymers by introducing azobenzene fragments in the side chain of poly(2-oxazoline)s. Three series of well-defined P(EtOx-co-AzBenOx) copolymers with molecular weights ranging from 6000 to 21 000 g mol⁻¹ and containing 6–21 mol% of azobenzene were synthesized via sequential hydrolysis/modification of poly(2-ethyl-2-oxazoline) homopolymers. The turbidimetry studies confirm the thermo-responsive behavior of the obtained copolymers, while spectroscopic studies confirmed the reversible isomerization of AzBenOx units under UV and visible light exposure. The presence of nanoparticles in aqueous solutions of the respective poly(2-oxazoline)s was confirmed by dynamic light scattering. Further DLS experiments revealed the changes in the size of these nanoparticles in response to UV irradiation.