Segmental Motions and Associated Dynamic Mechanical Thermal Properties of a Series of Copolymers Based on Poly(hexamethylene terephthalate)and Poly(1,4-cyclohexylenedimethylene terephthalate)

摘要

The dynamic mechanical thermal properties of poly(hexamethylene terephthalate)(PHT),poly(1,4-cyclohexylenedimethylene terephthalate)(PCT)and their P(HT-co-CT)random copplymers in the amorphous state were examined as a function of temperature and frequency.All the samples exhibited two main relaxation processes in the plot of tan S versus temperature:the primary alpha-relaxation associated with the glass transition and the secondary beta-relaxation attributed to the local segmental motions of mostly cyclohexylene rings for PCT and to cooperative motions of methylene,carboxyl,and phenylene groups for PHT.Both alpha-and beta-relaxation temperatures increased with increasing CT content.The activation energy of the alpha-relaxation increased with increasing CT content,whereas that of the beta-relaxation decreased.The sub-glassy secondary beta-relaxation processes of PCT and PHT were investigated in terms of the cooperativity of main-chain segmental motions.