Anaerobic adhesives and sealants have been developed primarily in industrial laboratories, and most of the published literature are patents. A number of papers have been published within the last two decades which discuss the reaction mechanisms of anaerobic adhesive cure [10-20].

A. Oxygen Inhibition

The polymerization mechanism of anaerobic adhesives is similar to that of other free — radical initiation systems except for the special ways in which the inhibiting effect of oxygen is used to delay the polymerization, and in the chemical activation that occurs at the metal surface.

The reaction rate of oxygen with free radicals is very high and the peroxy radical formed is a relatively poor initiator. When the supply of oxygen is used up within a thin

bond line, the propagation step can provide rapid development of adhesive strength. Although there is little disagreement about the importance of oxygen in the propagation step, the greatest interest and study has been directed to the initiation step in the process described above. The role of the bonding surfaces and the effect of different types of accelerators account for most of the literature on the cure mechanism of anaerobic adhesives.

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