Photoresponsive Gels Based on Cyclic/Linear Polymers: Efficient Synthesis and Property Difference
Cyclic architectures of polymers have shown unique properties or improved performance due to the lack of chain ends. Herein, we describe the first example of azobenzene-induced photoresponsive gels based on cyclic polymers made by azide–alkyne and boronic acid-diol “click” reaction. The properties of cyclic gels with different cyclic polymer sizes were investigated by comparing with those of linear ones made by the polymeric linear precursors. It was observed that the cyclic topology exerted larger influence on the properties of the gels. And more significant influences of topology were found from the cyclic gel with smaller cyclic polymer size. Rheological measurements revealed that the cyclic gels have higher storage modulus (G′) and loss modulus (G″) than the linear counterparts, indicating that the former is stiffer than the latter. The gel-to-sol transition and photo-healing of the gels induced by azobenzene were observed by irradiation with UV/Vis light. Nevertheless, the cyclic gel with the smaller cyclic polymer size showed a dull photo-responsive behavior due to the restrictions of transform of trans-cis isomer of azobenzene moieties imposed by cyclic topology. The results in this work showed that network mesh space, intramolecular and intermolecular interactions induced by macrocyclic architecture finally endow the functional cyclic gels unique properties.