Effect of methacryloxypropyl and phenyl functional groups on crosslinking and rheological and mechanical properties of ladder-like polysilsesquioxane hard coatings

The rheological and mechanical properties of photocurable ladder-like polysilsesquioxanes containing phenyl and methacryloxypropyl groups (LPMA) were investigated. LPMAs with various ratios of the two functional groups were synthesized through the hydrolysis and condensation reactions. The chemical structures of the synthesized LPMAs were confirmed using H1 NMR and FT-IR spectroscopy. The basic rheological properties of the LPMA solutions provided information about their flow properties prior to the curing stage, which was relevant for their application as a hard coating. The curing behaviors of the LPMA solutions under UV irradiation were scrutinized using real-time rheological measurements and rigid-body pendulum tests. These results were well correlated with the surface mechanical properties of the final cured LPMA films measured via nano indentation and scratch tests. The phenyl group was found to play a role in providing rigidity to the cured films, and the methacryloxypropyl group affected crosslinking performance. The physical properties of LPMA samples could be improved for application as a promising inorganic-organic hybrid coating by tuning the ratio of two functional groups.