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A study has been made of the dynamic mechanical relaxation behavior of a 97% cis polypentenamer and its hydrogenated derivatives. The starting polypentenamer is wholly amorphous and derivatives were synthe­sized having melting points from -11 to 131 °C and degrees of crystallinity from 2 to 80%. Three relaxations are dis­cernible in the temperature range from -160 °C to the melting point and these are labeled a, {3, and 1' in order of de­creasing temperature. The a relaxation occurs only in the crystalline derivatives. In the derivatives of low crystallini­ty, it originates from motions accompanying melting; in derivatives of high crystallinity, …