Synthesis, thermal characterization, and tensile properties of alipharomatic polyesters derived from 1,3-propanediol and terephthalic, isophthalic, and 2,6-naphthalenedicarboxylic acid

In this work, three alipharomatic polyesters-poly(propylene terephthalate) (PPT), poly(propylene isophthalate) (PPI), and poly(propylene naphthalate) (PPN)-were prepared and studied with the aliphatic diol 1,3-propanediol and the corresponding aromatic diacids. Their synthesis was performed by the two-stage melt polycondensation method in a glass batch reactor. The thermal characterization of these polyesters was carried out with different thermal techniques such as simultaneous thermogravimetry/differential thermal analysis, thermomechanical analysis (TMA), and dynamic thermomechanical analysis. From the recorded values for the glass-transition temperature (T-g) and melting temperature with all the aforementioned techniques, it could be said that they were in good agreement. According to the thermogravimetric results, PPT and PPI showed about the same thermal stability, whereas PPN seemed to be somewhere more thermostable. Remarkably, a transition existed immediately after Tg that was realized by the first derivative of TMA, and it was characterized as a midrange transition. For all polyesters, the average coefficient of linear thermal expansion was calculated with TMA. The secondary relaxations T-beta and T-gamma, recorded with dynamic mechanical thermal analysis, were mainly affected by the kinds of monomers. Concerning the mechanical properties, PPN had the highest tensile strength at break, whereas PPT had the highest elongation at break. (c) 2005 Wiley Periodicals, Inc.