This study was performed on cycloolefin materials. These polymers are more and more used in the cosmetic and pharmaceutical fields. Samples were subjected to an electron beam radio-sterilization. Different irradiation doses ranging from 25 to 150 kGy were used to study the irradiation effect on the structure and properties of the material. In this study, we were mainly interested in additive degradation, and in the modification of polymer thermomechanical properties, as elasticity, glass transition temperature, and swelling ability. Although the modification of the polymer chains was important, effect on thermomechanical properties was quite weak. (C) 2008 Wiley Periodicals, Inc.