Multiple melting behavior of poly(butylene succinate). I. Thermal analysis of melt-crystallized samples

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights of 1.1 x 10(5), 1.8 x 10(5), and 2.5 x 10(5), were cooled from the melt (150 degreesC) at various cooling rates (CRs) ranging from 0.2 to 50 K min(-1). The peak crystallization temperature (T-c) of the DSC curve in the cooling process decreased almost linearly with the logarithm of the CR. DSC melting curves for the melt-crystallized samples were obtained at 10 K min(-1). Double endothermic peaks, a high-temperature peak H and a low-temperature peak L, and an exothermic peak located between them appeared. Peak L decreased with increasing CR, whereas peak H increased. An endothermic shoulder peak appeared at the lower temperature of peak H. The CR dependence of the peak melting temperatures [T-m(L) and T-m(H)], recrystallization temperature (T-re), and heat of fusion (DeltaH) was obtained. Their fitting curves were obtained as functions of log(CR). T-m(L), T-re, and DeltaH decreased almost linearly with log(CR), whereas Tra(H) was almost constant. Peak H decreased with the molecular weight, whereas peak L increased. It was suggested that the rate of the recrystallization decreased with the molecular weight. T-m(L), T-m(H), T-re, and T-c for the lowest molecular weight sample were lower than those for the others. In contrast, DeltaH for the highest molecular weight sample was lower than that for the others. If the molecular weight dependence of the melting temperature for PBSu is similar to that for polyethylene, the results for the molecular weight dependence of PBSu can be explained. (C) 2002 Wiley Periodicals, Inc.