ABSTRACT: A dynamic mechanical study has been carried out on· a polypentenamer and its hydrogenated de­rivatives. The temperature range was from -160 to 130° and frequencies of 3.5, 11, and 110 Hz were employed. The starting polypentenamer was amorphous and the completely hydrogenated derivative resembled linear poly­ethylene with a melting point of 130° and a degree of crystallinity of 85%. Three relaxation regions were found in the temperature and frequency range investigated and these are labeled a, {:J, and -y in order of decreasing tem­perature. The a relaxation (5-115°, 3.5 Hz) is absent in the amorphous polymers and those of low crystallinity. It is composite in nature, consisting of three partially merged peaks. Two of these peaks may correspond to the in­terlamellar slip motion a􀁯d the intracrystalline motion concluded to be responsible for the -y relaxation in poly­ethylene. The f3 relaxation ( -75 to 0°, 3.5 Hz) arises from microbrownian segmental motion in the amorphous phase accompanying the glass transition. The -y relaxation ( ca. -115°, 3.5 Hz) is a secondary relaxation consisting of at least two components associated with the amorphous phase and the crystalline phase. The amorphous component appears to involve local reorientation of three or more backbone CH2 units and the crystalline component may in­volve the motion of chain ends present as defects within the crystal.