AbstractThe effects of moisture and rather large doses of reactor radiation (∼4 × 1011ergs/gm) on the dynamic properties of polymerized epoxy resins have been investigated over the temperature range of 80°‐450°K and at frequencies from 200 to 1400 cps. Data are presented for both unfilled and aluminum‐filled systems of a bisphenol A based epoxy, (Epon 828) cured with metaphenylenediamine. Moisture absorption (0.88%) causes a shift of the main glass transition near 440°K to lower temperatures (∼25 degrees for unfilled epoxy). This is similar to the plasticizing action of small molecules absorbed in other polymers such as nylon 6‐6. Irradiation to a dose of 4 × 1011ergs/gm (4 × 109rads) causes a shift to lower temperatures (∼50 degrees) of the onset of the main transition, and, in addition, results in both a shift to lower temperatures and a decrease in maximum height of the damping peak near 250°K. Chain scission, in a loosening of the structure and the breaking up of the partially flexible connecting groups, may be responsible for these