In free-radically cured adhesives such as acrylates (BMI as well, but not to
the same extent), oxygen is known to inhibit polymerization. In the bulk of the
material, once the finite level of oxygen is depleted, the polymerization process
will initiate.
At the adhesive fillet’s surface, however, depleted oxygen is continuously
replenished by oxygen molecules in the atmosphere. The end result can lead to
variations in cure and cured properties between the center of the die and outer
perimeter