Photoresponsive amphiphilic block macrocycles bearing azobenzene side chains

Abstract

Topological molecular architectures play a crucial role in the self-assembly of amphiphilic block copolymers. Many characteristics of macromolecules originate from the special properties of the ends of molecules. Herein, we synthesized well-defined cyclic block copolymers bearing hydrophobic azobenzene and hydrophilic carboxyl moieties in their side-chains, cyclic-PBHME_m-b-PAA_n, via sequential atom transfer radical polymerization (ATRP) and intramolecular Cu(I)-catalyzed azide/alkyne cycloaddition (CuAAC) cyclization reaction followed by the selective hydrolysis of tert-butyl ester. The successful synthesis of the amphiphilic block copolymers was fully characterized via conventional gel permeation chromatography, triple detection gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Via investigating the properties of the cyclic polymer, we observed that the cyclic structure displayed faster photoisomerization in solution than its linear precursor. Moreover, the cyclic copolymer exhibits larger changes in the size and morphology of the self-assembled aggregates upon 365 nm light irradiation as compared to its linear counterpart. These interesting findings show that the topological cyclic architecture greatly affects the photoisomerization of azobenzene and copolymeric packing behavior in micellar aggregates.