Topology-Reset Execution: Repeatable Postcyclization Recyclization of Cyclic Polymers.

Repeatable topological transformation of polymers for the modulation of material functions is a challenge. We have developed a method for repeatedly resetting a cyclic macromolecular architecture to a linear architecture by photostimulation, namely, topology-reset execution (T-rex) based on the photochemistry of hexaarylbiimidazoles (HABIs). We synthesized cyclic poly(dimethylsiloxane)s (PDMSs) of various ring sizes with HABIs linked in the chains. UV irradiation of the cyclic PDMSs produced telechelic linear PDMSs with triphenylimidazolyl radical (TPIR) end groups. After termination of UV irradiation, end-to-end recyclization occurred by the recoupling of TPIRs. The cyclic PDMSs also responded to ultrasound, which decreased their molecular weight (MW) by site-specific cleavage of in-chain HABI moieties, and we are able to reset the MWs by subsequent phototriggered T-rex. Furthermore, T-rex enabled solvent-free switching of the rheological properties of the materials while retaining the liquid character of PDMS.