Photocontrolled Hydrogen Bonding in Main-Chain Azobenzene Polymers

Incorporating azobenzene into polymer backbones enables reversible, light-driven modulation of macroscopic properties through trans – cis photoisomerization. Despite substantial work in this area, properties accessible at intermediate isomer populations remain underexplored, particularly in main-chain architectures. Here, structurally analogous azobenzene-containing polymers with and without urethane hydrogen-bonding motifs were synthesized. FTIR spectroscopy shows trans – cis isomerization disrupts hydrogen bonding in urethane groups, accompanied by suppressed crystallinity and a ≈30 °C decrease in T g . This change is well-described by a modified Fox model, suggesting isomerization acts to tune local interactions in analogy to random copolymers. By contrast, the non-hydrogen-bonding analogue required higher cis enrichment for photoinduced melting and showed little change in T g . Shear rheology reveals a change in dynamic moduli over ≈3 orders of magnitude as isomerization alters interchain associations, segmental mobility, and solidification. Collectively, these results establish targeted isomer populations and intermolecular interactions as a strategy for postpolymerization modulation of thermomechanical properties.