Mechanism silane coupling agent

Jones, F.R., Interfacial aspects of glass fibre reinforced plastics. In Jones, F.R. (Ed.), Interfacial Phenomena in Composite Materials. Butterworths, London, 1989, pp. 25-32. Chaudhury, M.K., Gentle, T.M. and Plueddemann, E., Adhesion mechanism of poly(vinyl chloride) to silane primed metal surfaces. J. Adhes. Sci. Technol, 1(1), 29-38 (1987). Gellman, A.J., Naasz, B.M., Schmidt, R.G., Chaudhury, M.K, and Gentle, T.M., Secondary neutral mass spectrometry studies of germanium-silane coupling agent-polymer interphases. J. Adhes. Sci. Technol., 4(7), 597-601 (1990). 

Although acid-base effects can be important in adhesion our studies indicate that bonding to metals through silane coupling agents is not by an acid-base mechanism, but probably through Si-O-M oxane bonds. As with glass, the hydrolysis and formation of oxane bonds are true equilibria, but the individual equilibrium constants are not known. 

Mechanisms of Silane Coupling Agents and Interfacial Studies... 

Our interest in silane coupling agents and in the preparation of silicates has led us to study the mechanisms involved in the various reactions. In a previous paper, we investigated the kinetics and mechanism of the alcoholysis of TMOS [13]. This present work studies the effects of changing the substituents on a para-substituted phenyl attached directly to the alkoxysilane. The alkoxysilane silanes used have only one alkoxy group present to eliminate complications from a competing second or third alcoholysis reaction. The resulting Hammett plot yields additional information on the mechanism of this reaction. 

The substrate/silane interphase and the silane/matrix interphase are equally important in considering the mechanism of reinforcement by silane coupling agents in composites. The mineral oxide/silane interphase is more well defined than a metal/silane or a silane/matrix interphase. For example, in the case of a metal substrate, surface oxides may dissolve into the silane layer or form a complex. In the case of the silane/matrix interphase, a diffuse boundary layer may exist due to dispersion of physisorbed silanes in the matrix phase or penetration of the matrix resin into chemisorbed silane layers. Many features of the interaction of a silane coupling agent with a polymer matrix are specific to the system, and thus the chemistry of the silane/matrix interphase must be characterized and defined for each system. 

Many different silane coupling agents are available for improving the adhesion between polymers and metals or fillers and fibers [1]. Although organofunctional silanes have been reported to be very effective in such adhesion applications, the exact mechanism by which they function has not been determined conclusively in certain cases. Several techniques have been used to characterize silane films formed on various substrates, such as glass, aluminum, and steel. Some of these methods are XPS [2, 3], FUR [4], IETS [5, 6], NMR [7], and Raman spectroscopy [8]. 

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