Controlling Polymer Melt Viscoelasticity via Photo-Reversible Hydrogen Bonding

In polymers, subtle variations in stereochemistry can drive profound differences in chain conformation, packing, and overall material performance. Typically, stereochemical effects are programmed during synthesis, and post-polymerization modulation remains challenging due to the high energy barriers associated with alkene isomerization. Incorporating photoresponsive azobenzene units provides a dynamic alternative, as these moieties undergo reversible trans–cis isomerization under light stimuli, producing planar-nonplanar geometric changes that directly influence chain packing and mechanical response. Here, we present a systematic study correlating azobenzene isomer populations with the thermomechanical properties of main-chain thia-Michael polymers. By controlling trans–cis isomer ratios through light exposure, we quantitatively relate isomer distribution to changes in glass transition temperature and mechanical behavior. Moreover, we show that incorporation of intermolecular hydrogen bonding amplifies photo-induced mechanical modulation. Collectively, these findings establish reversible stereochemical encoding as a robust strategy for designing tunable, light-responsive polymer materials.