Organofunctional silanes as adhesion promoters: direct characterization of the polymer/silane interphase

Organofunetional silanes can be used as coupling agents to promote the adhesion of organic matrices to inorganic substrates. Silane coupling agents are of the general structure YSi(OR)3, where Y is an organofunctional group selected for bonding to organic polymers while (OR) is a hydrolyzable group on silicon which can react with surface hydroxyl groups on the substrate. One mechanism of adhesion promotion by silanes has been postulated to be the interdiffusion of the coupling agent and the polymer to form an interpenetrating network. This paper reviews some earlier results using X-ray photoelectron spectroscopy to probe the polymer/silane interphase region and gives new results obtained using the technique of sputtered neutral mass spectrometry (SNMS). It was demonstrated that SNMS had the sensitivity necessary to detect the polymer/coupling agent interphase. It was found that interdiffusion of the coupling agent with the polymer was maximized when the solubility parameters of the polymer and coupling agent were matched.