Inorganic-organic nanocomposite networks: Structure, curing reaction, properties, and hard coating performance

This study reports the first structure and morphology details of octakis(acryloyloxypropyl)-octasilsesquioxane (POSS-Acryl8), a reactive inorganic-organic hybrid molecule, before and after photochemically crosslinked. POSS-Acryl8 was confirmed as an oblate ellipsoidal nanoparticle consisting of inorganic cage core (0.774 nm diameter) and chemically-bonded organic shell (1.447 nm thickness). The core volume fraction is only 0.95% in a single molecule, but drastically increases up to 18.8% in the neat bulk state and 31.9% in the photocured film state; the individual inorganic cores are eventually encapsulated with the networked shells (0.176 nm thickness) chemically interconnected with the neighbors. Based on such the highly networked structure and inorganic core reinforcement, the photocured POSS-Acryl8 exhibited exceptionally high optical transparency, glass transition temperature, surface hardness, and abrasion resistances. Due to the superior properties, clear hard POSS-Acryl8 coatings solved completely inherently poor surface hardness and abrasion resistances of conventional polymer window substrates and, furthermore, serious drawbacks in the eraser and steel wool abrasion resistances of glass window substrate. In addition, POSS-Acryl8 was found miscible with pentaerythritolylethyl tetraacrylate (PEEO-Acryl4) and thereby enhanced substantially the surface hardness and abrasion resistances of PEEO-Acryl4 through nanocomposite network formations. It turns out that the photocurable inorganic-organic POSS-Acryl8 hybrid and its composites with fully organic PEEO-Acryl4 are so suitable for optically clear hard top coating applications in advanced telecommunication, defense, automobile, and smart home appliance (smart and foldable phones, display devices, sensor windows, etc.).