Shackling Photoisomerization-Driven Self-Assembly of Azobenzene-Containing Ionic Alternating Metathesis Copolymers

Metathesis polycondensation between several kinds of α,ω-dienes and diacrylates containing an imidazolium cation or azobenzene moiety was performed under traditional conditions to afford photoresponsive ionomers with diverse chain structures, which were further tailored to explore the effects of connection sequences of monomers and noncovalent interactions of polymer chains on photoisomerization properties and self-assembly behavior. As proved by 1H NMR spectra, chain segments composed of two monomers are alternately or randomly distributed in the copolymers. The special alternating units and electrostatic forces endowed the alternating ionomers with shackling trans→cis isomerization transitions upon exposure to UV-light irradiation; simultaneously, driven ionomers self-assemble into unique nanosheets and nanospheres. Interestingly, three layers of nanosheets stacked in a three-dimensional direction to form large irregular nanosheets after UV-light irradiation, which differed from the significant deformation of the spherical nanostructures. Moreover, the nanosheet architecture remained unchanged even in different solvents; only the length displayed a distinct enlargement in the one-dimensional direction as the concentration increased. This work not only provided a facile and practical approach for constructing azo-containing metathesis ionomers but also expanded the optical properties and self-assembly morphologies.