The thermal behavior of three aromatic polyesters in a homologous series, poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT) was studied under hydrostatic pressure up to 200 MPa by using a high pressure differential thermal analysis apparatus. Confining fluid high pressure dilatometer was used to establish the volume–temperature curves (in both solid and liquid regions) from which volume change on melting of these polyesters at atmospheric pressure was determined. Single endothermic peak was seen for PET and PTT, whereas PBT showed double peaks above 50 MPa. Pressure coefficient of melting temperature at atmospheric pressure (dTm/dp(0)), was obtained from the quadratic fit. The dTm/dp(0) for PTT was newly determined to be 0.445 KMPa1, whereas for PET and PBT were 0.503 and 0.455 KMPa1, respectively, comparable to reported values. The dTm/dp(0) exhibited the odd-even behavior corresponding to odd and even number of methylene groups in the repeat unit. Enthalpy and entropy of fusion had the most influence on this coefficient. Entropy related to conformational and volume change were evaluated and the former was found to have a significant impact on the value of dTm/dp(0).
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