Quiescent crystallization and melting behavior of high temperature polymers

The quiescent isothermal crystallization and melting behavior of three members of the so called high temperature family has been studied. Poly(aryl ether ether ketone) [PEEK] an aromatic semi-crystalline polymer with the highest thermal properties among the three has shown step-like crystallization and melting behavior and so has poly(ethylene terephthalate) [PET]. Poly(ethylene naphthalene 2,6 dicarboxylate) [PEN] also displayed the same characteristics but not so clearly. In individual characterization through infrared analyses, differential scanning calorimetry and detection and recording of the amount of depolarized light during the process of bulk crystallization, PEEK has been observed to nucleate through three mechanisms. In addition, the general steps of the process of bulk crystallization have been controlled to demonstrate that there are three parallel stages of growth in bulk of these crystals. In a group characterization the molecular level of the process of crystallization has been studied. From the results, it was concluded that the regimes version of secondary nucleation theory does not give a straightforward explanation of the experimental facts. It is demonstrated, however, that a single regime type of behavior (III) for these polymers would be favored if experimental facts and calculations of this work, together with conceptual considerations, were applied. Finally, it is demonstrated that the process of crystallization develops through a step-like mechanism and that of melting is shown to occur in a reverse manner with three melting endotherms being manifest by such behavior.