Molecular dynamics of poly(butylene tert-butyl isophthalate) and its copolymers with poly(butylene terephthalate) as revealed by broadband dielectric spectroscopy

The dynamic behaviour of a set of copolyesters made of 1,4-butanediol, terephthalic acid and 5-tert-butyl isophthalic acid, as well as the two parent homopolymers was studied. Although the insertion of the tert-butyl isophthalate units in the main chain of poly(butylene terephthalate) modified the glass transition, the β relaxation did not change dramatically. By using broadband dielectric spectroscopy we have obtained a detailed picture of the dynamic behaviour of these systems. In all cases, a strong correlation between the α relaxation and the β relaxation above T_g was observed in accordance with recent proposals based on the coupling model.