Silane coupling agents chemical bonding theory

The examples summarized above are but indicative of the increasing body of evidence in support of the chemical bonding theory, and of the role of the silane organofunctional group in the formation of covalent bonds at the coupling agent/ matrix interphase by reaction or by co-polymerization with the formation of an interpenetrating polymer network. 

However, the chemical bonding theory cannot account for the increase in adhesion experienced between non-reactive matrices such as polyolefins and inorganic reinforcements in which chemical bonds will not be formed [4], This observation, among others, leads to an alternative proposal that an interphase composed of various constituents forms surrounding the reinforcement. This third phase in the composite is possibly formed through interdiffusion of physisorbed silane and matrix molecules in the interphase and perhaps via preferential adsorption of both matrix components as well as silane coupling agents on the reinforcement surface [5],... 

Chemical reaction theories propose that chemical reactions occur between the adhesive and the adherent forming primary chemical bonds. While it is unlikely that these theories are universally applicable to adhesives, chemical reactions may be present in some cases. Silanes, for example, are bifunctional molecules that are used as coupling agents [6]. One end of the molecule is intended to interact with a polymeric adhesive. The other end is intended to chemically react with atoms in the adherend s surface layer, such as oxygen in an oxide layer of a metal or the oxygen in a ceramic. 

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