Preparation of irrefrangible polyacrylamide hybrid hydrogels using water-dispersible cyclotetrasiloxane or polyhedral oligomeric silsesquioxane containing polymerizable groups as cross-linkers

Abstract

In this study, polyacrylamide (PAAm) hybrid hydrogels were prepared using water-dispersible single-structured cyclotetrasiloxane (CyTS-MNa) or polyhedral oligomeric silsesquioxane (POSS-MNa) containing polymerizable groups as cross-linkers, and the mechanical properties of the resulting hybrid hydrogels were evaluated. First, CyTS-MNa and POSS-MNa were prepared by the reaction of our previously reported cis–trans–cis cyclotetrasiloxane or polyhedral oligomeric silsesquioxane containing propylammonium trifluoromethanesulfonate groups with maleic anhydride, followed by neutralization with NaOH/methanol solution. The aqueous dispersions (1.0 wt%) of CyTS-MNa and POSS-MNa showed Tyndall effects. In addition, the dynamic light-scattering analysis performed on CyTS-MNa and POSS-MNa indicated that submicrometer aggregates were formed in water. Then, PAAm-CyTS-MNa and PAAm-POSS-MNa hybrid hydrogels were prepared by the free-radical polymerization of acrylamide (AAm) monomer in the presence of the resulting cross-linkers (CyTS-MNa and POSS-MNa), which can form aggregates in water, using potassium peroxodisulfate as an initiator in degassed water under an argon atmosphere at 65 °C. The hybrid hydrogels prepared using CyTS-MNa (feed molar ratio to AAm: 1.25%) and POSS-MNa (feed molar ratio to AAm: 0.625% and 1.25%) as cross-linkers exhibited a flexible nature (low elasticity) that resisted a strain of 97%.