Effect of polyhedral oligomeric silsesquioxane on water sorption and surface property of Bis-GMA/TEGDMa composites

2,2-Bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (Bis-GMA), one of the most important light-curable dimethacrylate resins, is widely used as dental restorative material. However, one problem of Bis-GMA is the high water sorption due to the hydrophilic hydroxyl (-OH) group, resulting in a short life in actual application. In this study, to overcome the drawback stated above, novel organic-inorganic dimethacrylate monomer containing polyhedral oligomeric silsesquioxanes (POSS), Bis-GMA-graft-POSS, is synthesized via the nucleophilic addition reaction of isocyanate functionalized POSS (IPOSS) and pendent hydroxyl group of Bis-GMA. Then the as-synthesized Bis-GMA-graft-POSS, of which hydroxyl group was substituted by hydrophobic POSS, is also introduced into the Bis-GMA/TEGDMA matrix to prepare a series of methacrylate-based hybrids for dental materials under visible light with camphorquinone and ethyl-4N,N-dimethy-laminobenzoae (EDMAB) as initiator and coinitiator, respectively. Compared to Bis-GMA/TEGDMA composites, water sorption of modified composites can be significantly reduced with the addition of Bis-GMA-graft-POSS. Moreover, the Bis-GMA/TEGDMA/POSS hybrids show hydrophobic surfaces, leading to much higher water contact angles than that of Bis-GMA/TEGDMA composites. The morphology of hybrids containing POSS was furthermore studied by X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS). The results show that POSS disperses in the matrix in noncrystalline form and tend to migrate to the surface of the modified composites that lead to the lower water sorption and higher water contact angles. These results are very useful for design of novel methacrylate monomers and clinical application.