Comparison of dynamic mechanical relaxation processes at cryogenic temperatures in polyesters

The relaxation behavior of poly (1,4-cyclohexylenedimethylene terephthalate) over the temperature range 4.2[ddot]-300[ddot]K is reported. The trans polymer shows a strong γ relaxation at 175[ddot]K (1 Hz) and a Δ relaxation at 45[ddot]K, whereas the γ and Δ peaks of the cis polymer are at 200[ddot] and 48[ddot]K, respectively. A copolymer of the two isomers shows a composite γ peak which is resolved into two components associated with the trans and cis glycols. A mechanism for the γ peak involving motions of short chain segments is proposed and discussed with reference to the analogous relaxation process in polyethylene terephthalate. The effects of crystallinity and orientation on the γ and Δ relaxations are also considered.