One of global efforts to address the growing environmental concerns pertaining to energy consumption in automotive and aerospace industries is to replace conventional materials with lightweight alternatives. In this regard, development of industrially viable high-temperature polymeric foams is of significant interest. Generating microcellular structures with lightweight thermoplastics would not only provide weight reduction but also tailorable properties based on the cell architecture. Furthermore, utilizing environmentally benign physical blowing agents, for instance CO₂ and N₂, to develop such structures would additionally reduce the environmental footprint of manufacturing processes. Despite the economic and the environmental advantages of high temperature polymeric foams, the development is still at its inception. There is a limited number of studies on the foaming of high temperature polymers and the majority are based on the two-step batch foaming process, in which cell nucleation was induced thermally through rapid heating. Although the results may be meaningful, it is not applicable to continuous foaming processes that utilize pressure quench as a means of inducing thermal instability. In this regard, the present dissertation is dedicated to investigating various aspects of processing high-temperature sulfone polymer foams and making a transition from small scale batch to continuous processes.

The study commenced with fundamental research on the solution properties of sulfone polymers and CO₂. Empirical as well as theoretical determination of gas solubility and observation on plasticizing effects of CO₂ on the thermal behaviors of polysulfone (PSU) and polyethersulfone (PES) were conducted and discussed in relations to foaming. The one-step batch foaming process was employed to discern the effects of processing parameters on the foaming behaviors of PSU and PES. Uniform cellular structures exhibiting high cell densities ranging up to 10¹⁰ cells/cm³ were developed affirming that the pressure quench method was effective in producing high density foams. Subsequently, foam injection molding techniques were implemented for the continuous production of PSU foams. Impact and tensile properties of the foams were characterized and analyzed based on the parameters of cellular structures. Lastly, graphene nanoplatelet (GnP) was introduced in the processing of PES foams. The effectiveness of GnP as a cell nucleating agent, and the effects of cell structures on the electrical performance of the nanocomposites were investigated. Overall, the dissertation provides a comprehensive framework of high-temperature foam processing that focuses on process-structure-property relationships of sulfone polymer foams.