Divinylazobenzene-Q-Cage Silyloxy-Silsesquioxane-Based Reversible Photoactuatable Network Polymer Sponges

The development, analysis, characterization, and solvent preference of photoresponsive hybrid 4,4'-divinylazobenzene and octa-(dimethylsiloxy)-silsesquioxane (Q₈M₈ ^H) networks were investigated. The dynamic gel systems are formed through hydrosilylation chemistry and respond to visible and UV light, expanding and contracting to give them sponge-like properties. Their solvent preference and loading capabilities are analyzed and compared to an analogous system, and general characteristics are illustrated through UV-vis cycling, FTIR, TGA, DMA, and SEM imaging. Analysis using advanced spectroscopic methods, such as SAXS and USANS, to further understand the structural and polarity changes in these materials upon light irradiation has been unsuccessful due to the stochastic linking and reactivity of these systems. We find that using a shorter, more rigid azobenzene yields a photoresponsive sponge comparable to that of 4,4'-diallyloxyazobenzene, with a higher initial shrinkage response. SAXS spectroscopic analysis shows little overall change in structural size between static and UV-irradiated samples in their toluene-swollen states, but there are distinct changes in overall structural organization, as evidenced by the scattering profiles and, in limited cases, decreases in the water contact angles on dried gel surfaces, which are also consistent with swelling and UV-vis studies.