Silyl Peroxide-Some Chemical and Physical Effects on Adhesion Promotion

Silyl peroxides have previously been shown to promote the adhesion in a broad range of polymer/substrate and polymer/polymer systems. A correlation between the chemical composition of silyl peroxides and their ability to bond clearly exists. Their effectiveness is usually enhanced with increasing number of reactive sites. Whilemany reactive functional groups are useful, the presence of at least one peroxy group appears to be a necessity. Silyl peroxides are heat-activated. Strength of joints made of silyl peroxides are shown to depend on the extent of their dissociation which can be accelerated or retarded with known radical accelerators or retarders, respectively. Adhesion is believed to result from a sequence of silyl peroxide initiated, free radical reactions taking place during the curing step. This hypothesis is consistent with the kinetic behavior of the silyl peroxides. Internal reflection infrared study reveals that the areas immediately surrounding the interface are diffused layers of siloxanes and the substrate molecules. The possibility of chemical linking of the silyl peroxide fragments to the polymeric phase(s) is suggested. Silyl peroxide promoted joints exhibit good hydrolytic and thermal stabilities. However, the measured adhesive strength is also affected by the morphology of the polymer employed in the system. Results of a quenching study are presented.