Journal of Macromolecular Science R  , Part B: Physics, 49:470–478, 2010 Copyright © Taylor & Francis Group, LLC ISSN: 0022-2348 print / 1525-609X online DOI: 10.1080/00222340903583443 High-Pressure Analysis of the Multiple Melting Endotherms of Poly(ethylene succinate) and Poly(butylene succinate) DAVID R. ROHINDRA, KEIICHI KUBOYAMA, AND TOSHIAKI OUGIZAWA Department of Organic and Polymeric Materials, Graduate School of Engineering, Tokyo Instituteof Technology, O-okayama, Meguro-ku, Tokyo, Japan The origin of the multiple melting peaks in two linear polyesters, poly(ethylene succi- nate) (PES) and poly(butylene succinate) (PBS), of isothermally crystallized samples was investigated by differential scanning calorimetry (DSC) at atmospheric pressure and high-pressure differential thermal analysis (HP-DTA) at elevated pressures. In PES, the DSC melting curves showed three endothermic peaks at slow heating rates, which decreased to two with increasing heating rates. The HP-DTA curves showed that the area (qualitative) and peak height of the high-temperature peak decreased with increasing pressure and merged with the low-temperature peak at pressures above 450 MPa. This behavior supported the melting, recrystallization, and remelting model for the observed multiple melting endotherms. In PBS, the DSC melting curves were similar to those seen in PES. The HP-DTA curves were also similar to PES up to 400 MPa, but above this pressure the area and the peak height of the high-temperature peak and the temperature difference between the high- and low-temperature peaks re- mained unchanged. This observation suggested that the two peaks in PBS were due to the melting of two populations of crystals with different lamellar thickness originally present in the sample. The multiple melting behavior in isothermally crystallized PBS is proposed to incorporate both the melting of two populations of crystals and melting, recrystallization, and remelting. Keywords high-pressure DTA, isothermally crystallized, multiple melting peaks, poly(butylene succinate), poly(ethylene succinate) Introduction Multiple melting endotherms are often found in the heating scans of many semicrystalline polymers crystallized either isothermally from the melt at selective crystallization temper- atures or nonisothermally at slow cooling rates. [1–4] The origin of these complex multiple melting behaviors has been extensively studied and several models have been proposed to explain this phenomenon based on the polymer and its thermal history. The proposed models are (i) melting, recrystallization, and remelting during heating, (ii) presence of more Received 18 June 2009; accepted 23 June 2009. Address correspondence to Toshiaki Ougizawa, Department of Organic and Polymeric Materials, Graduate School of Engineering, Tokyo Institute of Technology, 2-12-1-S8-33, O-okayama, Meguro- ku, Tokyo 152-8552, Japan. E-mail: tougizawa@op.titech.ac.jp 470