Multiple melting behavior of poly(butylene-2,6-naphthalate)

Multiple melting behaviors of poly(butylene-2,6-naphthalate) (PBN) prepared by various crystallization conditions were studied by differential scanning calorimetry at a heating rate of 10°C/min. It is found that the crystallization rate of PBN is so rapid that the glass transition temperature cannot be detected by simply heating the quenched sample. Two melting peaks are generally perceptible in a heating scan for isothermally crystallized samples that can be properly explained by the model proposed by Zhou and Clough (Polym Engng Sci 28 (1988) 65). The low-temperature melting peak can be ascribed to the melting of primary and secondary crystals generated during the crystallization or annealing process, while the high-temperature melting peak comes from the significant contribution of the melting of recrystallized species formed during heating. The step-crystallization was performed to clarify the relationship between the melting behavior and crystal modifications of PBN. In this study, it is found that the melting behavior of PBN is independent of the crystal forms and dominated by the crystal lamellar thickness and the perfection of crystals, which are dependent upon the thermal history. Finally, an equilibrium melting temperature of 276°C is obtained for the neat PBN, which is lower than that published in the literature.