Main‐chain Macromolecular Hydrazone Photoswitches

Abstract

Hydrazones—consisting of a dynamic imine bond and an acidic NH proton—have recently emerged as versatile photoswitches underpinned by their ability to form thermally bistable isomers, (Z) and (E), respectively. Herein, we introduce two photoresponsive homopolymers containing structurally different hydrazones as main‐chain repeating units, synthesized via head‐to‐tail Acyclic Diene METathesis (ADMET) polymerization. Their key difference lies in the hydrazone design, specifically the location of the aliphatic arm connecting the rotor of the hydrazone photoswitch to the aliphatic polymer backbone. Critically, we demonstrate that their main photoresponsive property, i.e., their hydrodynamic volume, changes in opposite directions upon photoisomerization (λ=410 nm) in dilute solution. Further, the polymers—independent of the design of the individual hydrazone monomer—feature a photoswitchable glass transition temperature (Tg) by close to 10 °C. The herein established design strategy allows to photochemically manipulate macromolecular properties by simple structural changes.

Photo- and halochromism of spiropyran-based main-chain polymers

“…The substitution-site dependence of M n in ADMET polymerization is also observed in hydrazone-based main-chain polymers. 38 …”

Access to Main-Chain Photoswitching Polymers via Hydroxyl-yne Click Polymerization

“…We have previously demonstrated the feasibility of head-to-tail Acyclic Diene METathesis (ADMET) polymerization for the realization of responsive polymers having photoswitching moieties as main-chain active groups. , Macromolecular structures obtained via ADMET were further post-modified based on the formation of the internal acrylate bonds in their polymer backbone . However, the use of costly Hoveyda-Grubbs second generation (HG-II) catalysts potentially limits the application scope of this technique.…”