Silsesquioxanes (SSO) were synthesized by the hydrolytic condensation of (3-glycidoxypropyl) trimethoxysilane (GPMS). Their structure was characterized by FTIR and NMR (H-1, C-13, Si-29), and the molar mass distribution was determined by UV-MALDI-TOF MS. Films were synthesized by adding the stoichiometric amount of ethylenediamine to SSO solutions in ethanol, dip-coating over glass substrates, and curing using an appropriate thermal cycle. The transmittance of the films was measured by UV-VIS-NIR scanning spectrophotometer (SSP); hardness and modulus were determined with the continuous stiffness measurement (CSM) technique of an instrumented-indentation testing (IIT) device. The effect of the substrate on the coating system was analyzed. (C) 2004 Kluwer Academic Publishers.