The Study Of Complicated Thermodynamics Properties For Polymers By Repeat Step-Scan DSC Method

With the development of differential analysis technique and the improvement of Differential Scanning Calorimetry(DSC),people become more interested in the study of basis thermodynamics.Being inspired from the study of PE560Da,we developed a new method of repeat Step-Scan DSC,and made some preliminary investigation about POE of different comonomer concentration by step-scan DSC. We discovered a new phenomenon about reversible melting ,with separation of three curves, which is more regular than the results obtained from TMDSC, and not controlled by the parameters of DSC.And its repeatability is 100% within the rang of error.There is no separation of three curves before melting , but the area of the first heating curve increases rapidly in the melting range, where the thermodynamic Cp of the first heating run is practically largely irreversible. The cooling run and the subsequent heating curve are almost identical in the melting region. This is suggested that the second heating run is fully reversible. At the end of the melt, three curves overlap again. The irreversible part arises from crystallization behavior, correlated to the degree of crystallinity, as increasing with it.Combination of the crystal structure and the results of repeat Step-Scan DSC for POE-new, we can found that the melt of fringed-micellar crystal is reversible. The melting endothermic peak area ratio of the second heating curve and the first heating curve is increasing with the comonomer content.In order to study the nature of the new phenomenon,we investigated HDPE and EP-blocks by the same method.The result was that HDPE also has reversible melting peak.It is suggested that reversible melting is not the unique feature of POE. Before repeat Step-Scan DSC,we made different heat treating for HDPE, and found that ,to some extent, different crystallization condition and thermal history have different impact forirreversible melting and reversible melting. A1, one of EP-blocks, has two melt endothermic peaks. The one at high temperature arises from PP segment crystallization, which has apparent reversible melting peak. The other one is from PE segment crystallization, which has separation of three curves, but the reversible melting peak is very small. The other one of EP-blocks, A2, has only one melting endothermic peak that is from PE segment crystallization. And it has the obvious reversible melting peak with the separation of three curves.In addition,so as to investigate the universality of the new phenomenon, we also studied Hg, paraffin, n-tridecane and H₂O/PAA.