Memory effect in isothermal melt-crystallization of poly(p-phenylene sulfide) single crystals grown from dilute solution

A structurally well-characterized starting material was considered crucial to understand the influence of the sample treatment in the melt on polymer crystallization kinetics. In the present work, we have studied the isothermal melt-crystallization of poly(p-phenylene sulfide) (PPS) as a function of the thermal history of the sample (dwell temperature and time in the melt state), employing single crystals of the polymer grown from dilute solution as the starting material. The kinetics of the process was followed by differential scanning calorimetry and the data were described in terms of the Avrami theory. It was shown that the structure of the sample and its thermal history affects the mechanism and the rate of the transformation strongly. As the severity of the melt treatment increases, the nucleation mechanism changes from athermal (n=3) to thermal (n=4) and the kinetics of the crystallization does not reach a plateau even when the predetermined nuclei are destroyed completely, indicating an influence of the thermal history on the nucleation rate N˙ and/or crystal growth rate G. This parameter seems to be influenced by the melt treatment. An analysis of the melting behavior of the so-crystallized polymer shows that a large dwell temperature in the melt state produces more imperfect crystals.