The aim of this study is to develop coatings on polymer substrates with a combined increase in oxygen barrier performance and toughness, based on SiOx coatings modified with multifunctional organo-silane polymers of controlled polarity and reactivity. As a first step, the formation mechanism of the amino-silane/SiOx interphase was determined using various analytical techniques (DSC, FTIR, ICP, AFM, XPS and XRF). Then the resulting oxygen permeability and cohesive properties of the nanocomposite barrier coating were investigated by means of tensile tests carried out in-situ in a scanning electron microscope and a permeation cell, respectively. It was found that the results and their analysis led to a better understanding of the role of the interfacial and/or interphasial properties in both the mechanical and permeation behavior of such nanocomposites.