(573g) Synthesis and Characterization of Ladder-like Polysilsesquioxanes for Hard Coating Films

Organic-inorganic hybrid materials that combine the advantages of the inorganic material (e.g., rigidity, mechanical property) and the organic material (e.g., flexibility, dielectric, and processability) have been widely used as protective hard coating films for mobile phones, touch panels, optical lenses and automobiles. Recently, ladder-like polysilsesquioxane (LPSQ) is regarded as one of promising candidates for the hard coating material due to its good mechanical properties and good solubility in a wide range of organic solvents. In this work, a series of LPSQs containing the UV-curable methacryloxy propyl (MA) group and different organic functional (R) groups (propyl, hexyl, cyclohexyl, phenyl or naphthyl) were synthesized in order to understand the effect of the organic functional groups on their film properties. All the LPSQ hard coating films prepared by a UV curing process exhibited the excellent optical transparency with transmittance higher than 90% in the visible light range. Importantly, the mechanical properties of the LPSQ films are determined predominantly by the chain rigidity of the organic functional groups although they can also be affected by the chain packing density to some extent. Hence, the LPSQ film containing the naphthyl group exhibited the highest hardness, elastic modulus and scratch resistance, which was attributed to its increased chain rigidity endowed by the high degree of aromaticity. This study suggests the key factor when designing mechanically durable, scratch resistant hard coating films is the chain rigidity of the film network.