Foldable hard coating materials based on reaction-controlled polysilsesquioxane resin for flexible electronic devices.

• The new synthesis route of siloxane-based materials is presented. • The key factor of hardness and modulus of hard coating material is both Mw and PDI. • The hard coating layer is studied with nanoindentation analysis. • 2-step sol-gel synthesized hard coating improved surface hardness by 32 %. Flexible but still hard coating materials have been paid attention for applications in flexible electronic devices, as efforts to substitute glasses. However, there have been little approaches to find out control parameters determining their flexibility and hardness. Here, we present reaction-controlled polysilsesquioxane (PSQ) resins with improved flexibility and hardness. In this study, the effects of various reaction conditions on the molecular weight of the PSQ resins are investigated in terms of reaction time, and absence of byproducts, accompanying the analysis of mechanical properties of the corresponding films using nanoindentation. With the reaction-controlled PSQ resins by removing byproducts such as alcohols, the molecular weight could be increased up to 44 % compared to PSQ containing the byproducts. The surface hardness and modulus of hard coating films are also enhanced by 32 % and 13 % compared to that from original PSQ resin, respectively. Finally, we demonstrate folding reliability for 100 k bending cycles at various bending radii of 6 to 1 mm that shows improved warpage property with less irreversible deformation upon the folding test. [ABSTRACT FROM AUTHOR]