This dissertation addresses the crystallization, melting and morphological characteristics of selected high temperature poly(arylene ether) based polymers. The first part deals with the studies carried out on a series of biphenol and hydroquinone based novel poly(ether ether sulfide)s which were investigated with respect to their crystallization and morphological behavior. The biphenol based poly(ether ether sulfide)s (T_g = ca. 142 °C, T_m = ca. 347 °C, T_m° = 371 °C), and the hydroquinone based poly(ether ether sulfide)s (T_g =ca. 100 °C, T_m = ca. 243 °C, T_m° = 292 °C) were studied to evaluate the crystallization characteristics and to compare the observed behavior with that displayed by commercial polymers like PEEK and PPS. Isothermal melt crystallization kinetic studies of the sulfides were carried out and analyzed using the Avrami formulation. The results were used to compare the behavior of the polymers at different crystallization temperatures and for the different molecular weights. Non-isothermal crystallization kinetics of the same polymers were investigated from the melt; in all cases, the Ozawa analysis could not describe the evolution of crystallinity. The non-isothermal data were hence analyzed using the conventional form of the Avrami equation, which yielded good fits to the data. The Avrami parameters obtained in this analysis do not, however, have the same physical significance as in the case of isothermal crystallization. Still, this approach is shown to be useful as a means of comparing the rates of crystallization. Spherulitic growth rate and morphological studies were carried out on the hydroquinone based poly(ether ether sulfide)s. At all crystallization temperatures, distinct populations of two kinds of spherulites were formed, with a population of coarse textured spherulites exhibiting a higher growth rate (Type II) than a population of fine textured spherulites (Type I). The morphology of these spherulites have been studied here using a variety of techniques, in conjunction with growth rate studies under a variety of conditions, in order to explain the occurrence of such phenomena. The differences in the growth rate and morphology have been attributed to differences in film thickness; the causes behind such effects, however, still remain unclear.

The second part of this dissertation involves the study of a series of high performance polyimides. Semicrystalline polyimides based on an all para-linked diamine, 1,4-bis(4-aminophenoxy)benzene (TPEQ diamine) and oxydiphthalic dianhydride (ODPA), endcapped with phthalic anhydride (PA) (T_g = ca. 230 °C, T_m = ca. 420 °C), and based on a PA endcapped meta-linked diamine, 1,3-bis(4-aminophenoxy)benzene (TPER diamine) and 3,3’, 4,4’-biphenyltetracarboxylic dianhydride (BPDA), (T_g = ca. 215 °C, T_m = ca. 395 °C) were investigated. The thermal stability of these polymers above T_m was investigated by studying the effect of time and temperature in the melt on the crystallization, melting and rheological! behavior of these polymers. The TPER polyimide was shown to display exceptional thermal stability as evidenced by the fact that residence in the melt at temperatures as high as 430 °C for times up to 30 min did not result in any loss of crystallizability or degree of crystallinity of the sample. The nature of the endgroups was found to play a critical role in determining the thermal stability of these polyimides under extreme conditions. In this investigation, the thermal stability of these polyimides has been compared to that of a commercial polyimide “New TPI”. The TPER based polyimide displayed considerably superior stability and crystallizability characteristics compared to New TPI.

The last section of this dissertation deals with the structural changes accompanying cold-crystallization in New TPI, as a function of crystallization temperature and time. The changes in the glass transition, melting behavior and morphology accompanying the crystallization process were followed by a combination of thermal analysis, dynamic relaxation methods, and x-ray scattering. Increasing crystallization temperatures caused a decrease in the glass transition temperature, an increase in the degree of crystallinity, and increases in both the average lamellar and amorphous layer thicknesses. Increasing crystallization time at a given crystallization temperature produced an increase in T_g, an increase in the degree of crystallinity, and a decrease in the average lamellar thickness. The results have been rationalized based on secondary crystallization occurring in the polymer leading to the formation of a bimodal distribution of lamellar thicknesses.