Effect of Copolymerization in the Dynamics of Poly(trimethylene terephthalate)

The structure-dynamics relationships in random copolymers of poly(trimethylene terephthalate) and poly(neopenthyl terephthalate) (PTT−PNT) have been investigated by means of X-ray scattering and dielectric loss spectroscopy experiments. The results show that the incorporation of neopenthyl terephthalate units into PTT chain decreases the ability to crystallize of the resulting copolymers as compared to that of PTT. The subglass dynamics of the copolymers is characterized by the existence of two processes, β1 and β2. We propose that the high frequency secondary relaxation β1 is associated with the most flexible part of the repeat unit, whereas the low frequency mode β2 has been assigned to the carbon of the ester groups linked to the aromatic ring. On the contrary the poly(neopenthyl terephthalate) (PNT), presents only one subglass process, that we hypothesize to have the same origin of the relaxation of β2 relaxation in PTT. The segmental dynamics for the amorphous specimens, characterized by the α-process, follows an expected molar ratio behavior. A particular effect characterized by a reduction of the segmental mobility induced by the presence of the counits is observed in the copolymers.