It should be noted that side effects are possible when using adhesion promoters/coupling agents as additives in adhesives and coatings, usually beneficial but not invariably so.
Beneficial effects from the use of titanates include deagglomeration, improved wetting, improved corrosion resistance, increased hydrophobicity, electrical conductivity in conducting systems, and acid resistance. The overall rheology of filled systems may be changed by both titanates and silanes requiring products to be reformulated. Silanes, particularly amino silanes, may function as curing agents or accelerators in epoxide and urethane adhesives, thereby reducing the pot life of a mixed system. These side effects should be considered in the selection or rejection of an adhesion promoter even if adhesion is the primary concern.
In attempting to cover such a wide and diverse topic as adhesion promoters in a short chapter, the author is aware of many gaps in the information presented and the omission of many aspects of theoretical and practical interest; it is hoped that the references quoted will fill many of these gaps. It has been demonstrated that adhesion promoters/coupling agents have a major role to play in the development of adhesive technology, but only if due regard is paid to the importance of matching the promoter to the substrate and the polymer, pH effects, solution age, dosage, and film thickness. Plueddemann concludes that the performance of coupling agents may depend as much on the physical properties resulting from the method of application as on die chemistry involved.