| Aromatic poly(ether ketone)s (PEKs), such as poly(ether ether ketone) (PEEK?), are a class of high performance engineering thermoplastics known for their excellent combination of chemical, physical and mechanical properties. This class of advanced materials has received considerable attention for their potential applications in aerospace, automobile, electronics, and other high technology fields.The study on the crystallization behavior of polymers is of importance for their wider use and the theory of polymer physics. For the conventional PEKs are semi-crystallized polymer materials, their crystallization behaviors, crystallinity and crystallization structure, etc. would afect their property and application to some degree. On the other hand, there is physical aging phenomenon happens for many kinds of polymeric materials, including PEKs, and it would effect some properties of polymers. Therefore, The aging has been an attractive subject in polymer field for long time. In the period of my Ph.D. degree, I focused on studying the crystallization and physical aging behaviors of PEKs. The multiple melting behaviors of PEEK? have received a great deal of attention. I have studied the melting behaviors of both melt and glass crystallized PEEK by alternating differential scanning calorimetry (ADSC), DSC and WAXD. The double melting phenomenon showed on the DSC heating curves of PEEK glass-crystallized at 180 and 220 oC for different times, confirmed that PEEK really exhibits the double melting behavior. WAXD patterns of PEEK samples, which showed two melting endotherms in DSC heating traces, are the same in terms of diffraction peaks. This indicates that only one crystal structure exists in samples, regardless of their melting behavior. The DSC curves at different heating rates of PEEK samples crystallized at 180 and 220oC for 13h, showed increasing low endotherm peak and decreasing high endotherm peak with the increasing heating rate, which proved the melt-recrystallization phenomenon occurred. On the other hand, there are low endothermic peak in the DSC heating traces of PEEK crystallized at 190, 210, 220, 310 and 320oC for only 0.5min. Above results proved that the double melting behavior is resulted from the melting of primary crystal and secondary crystal separately, and the secondary crystal proceeded recrystallization almost at the same time. We also measured both the glass-crystallized and melt-crystallized PEEK samples at different temperatures for different times. For the two kinds of samples, the results are similar. After the low endotherm, which is the melting of secondary crystals, melting and recrystallization in regions previously occupied by secondary crystal or by lower melting primary crystals, contribute to the broad exotherm seen in the nonreversing signal. This process occurs through the melting of primary crystals and continues to the final melting region. The broad reversing melting over the same range of the nonreversing exothermic signal supports the interpretation.So we think the PEEK for both of the two crystallization conditions exhibited secondary crystal melting in the low melting region, which is regarded as the low endothermic peak, followed by the melting of imperfect primary crystals superimposed with a large recrystallization contribution. Primary crystal melting broadly overlapped with the melting of recrystallized species and contributed to the broad highest endotherm, which is the high endothermic peak. We have successfully synthesized two high-performance poly(ether ether ketone)s, 6F-PEEK and m-TPEEK. They are promising materials as electronic and optical devices. In order to know the thermal stability of PEEK?, 6F-PEEK and m-TPEEK, we study their physical aging behaviors by MDSC. All the three kinds of film samples were aged at 20oC lower than their glass transition temperatures, separately. The data have been analyzed in terms of total, non-reversing heat flows and complex heat capacities. To all of these three kinds of materials, the experimental re...
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