It is an antioxidant, and it is thought to be more stable and has a longer shelf life than Vitamin E. However, according to dermatologist Leslie Baumann, Tocopherol Acetate is not as easily absorbed by the skin as Tocopherol and thus does not have the same incredible photoprotective effects.

See also:
Antioxidant
Vitamin E

Ref:
Leslie Baumann, MD, Cosmetic Dermatology, 2nd edition