Network Reorganization of Dynamic Covalent Polymer Gels with Exchangeable Diarylbibenzofuranone at Ambient Temperature

Reversible bonds and interactions have been utilized to build stimuli-responsive and reorganizable polymer networks that show recydability, plasticity, and self-healing. In addition, reorganization of polymer gels at ambient temperature, such as room or body temperature, is expected to lead to several biomedical applications. Although these stimuli-responsive properties originate from the reorganization of the polymer networks, not such microscopic structural changes but instead only macroscopic properties have been the focus of previous work. In the present work, the reorganization of gel networks with diarylbibenzofuranone (DABBF)-based dynamic covalent linkages in response to the ambient temperature was systematically investigated from the perspective of both macroscopic and microscopic changes. The gels continued to swell in suitable solvents above room temperature but attained equilibrium swelling in nonsolvents or below room temperature because of the equilibrium of DABBF linkages, as supported by electron paramagnetic resonance measurements. Small-angle X-ray scattering measurements revealed the mesh sizes of the gels to be expanded and the network structures reorganized under control at ambient temperature.