The adhesion promotion mechanism of organofunctional silanes

Abstract

The adhesion promotion mechanism of organofunctional silanes has historically been attributed to the formation of an “interpenetrating polymer network” between a polymerized silane film and the polymer. This notion was investigated by formulating and testing two hypotheses. First, if the adhesion promotion is due to the formation of an interpenetrating polymer network, variation in the time-temperature profile of the bonding conditions should alter the extent of interdiffusion and thus interfacial strength. Second, if the adhesion promotion is due to compatibility and penetration of the silane organofunctional group, not the bulk silane film, variation in the structure of that group should change interfacial strength. Direct interfacial strength measurements using single-particle composites show that variation in the time-temperature profile of bond formation does not significantly affect interfacial strength. However, use of a series of aminofunctional silanes (with constant C : N ratio and identical surface energetics) revealed a relationship between length of the aminofunctional group and interfacial strength. These results suggest that the adhesion promotion for the system studied is controlled by compatibility and penetration of the silane organofunctional group. Whereas all of the interfaces studied here featured poly(vinyl butyral), the conclusions should apply to all amorphous polymeric materials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1025–1033, 1998