HEATING RATE DEPENDENCE OF POLYMER MELTING POINTS

In the reported experiments, the melting points (T//m) of small quantities (ca. 0. 1 mg) of polyethylene (PE) single crystals in the dried state and in suspension were determined as a function of heating rate. Melting points were also obtained for large amounts (ca. 3 mg) of dried-down crystals. It has been reported previously that PE crystals of high molecular weight possess a single melting point and this T//m decreases with increasing heating rate. However, all samples in our study show multiple melting behavior. Moreover, suspension samples show little or no variation in the various peak temperatures with heating rate. There is some dependence of T//m on heating rate for small dry samples but the change of T//m is not nearly as great as previously reported. These small changes can be the result of the relatively poor resolution of small dry samples compared to suspension. Differences between the behavior reported here and those of other authors can be explained on the basis of the relative contributions to the various melting endotherms.