Dynamics in renewable sourced random poly(trimethylene 2,5-furanoate-co-trimethylene suberate) copolymers: isobaric fragility and compensation law in secondary relaxations

Abstract

This article presents an experimental study on the relaxation dynamics in a series of random copolymers with optimum gas barrier properties based on bio-friendly monomers. The relaxation response of poly(trimethylene 2,5-furanoate-co-trimethylene suberate) copolymers is examined in the glassy and viscoelastic regime via frequency-domain spectroscopies (dielectric and mechanical). We report lower values of dynamic fragility, a dimensionless index introduced in 1985 [Angell, Relaxations in Complex Systems ; Eds. K.Ngai and G.B. Wright, National Technical Information Service, US Department of commerce, Springield, VA, 1985, p. 1], in comparison to conventional polyesters used in industry, such as poly(ethylene terephthalate). We propose that this is consistent with their low permeability to gases. The sub-glass dynamics is complex and can be described by two local modes, β1 and β2, whereas for the homopolymer PTF and copolymer with the lowest suberate unit content we detect a single β relaxation. Our study also reveals that sub-Tg relaxations obey the so-called compensation law.