Advances in the field of microelectronics have contributed to component miniaturization and therefore have augmented the power densities, resulting in thermal management concerns. High power densities generate an excess amount of heat, which leads to increases in device operating temperature, reduced performance and surges in hardware failure. Traditionally, heat sinks have been used to conduct excess amount of generated heat away and keep the component’s temperature to below the critical level in order to prevent the device from permanent damage. In particular, they are often sensitive to thermal cracking and are of limited utility in small and thin packages [1]. Due to this challenge, discovering new multifunctional materials with outstanding thermal conductivity is becoming more important.

Thermally conductive polymer composites can be considered as new alternatives to electronic packaging materials, which are usually based on epoxy. Higher thermal conductivity can usually be obtained by adding larger amounts of filler. However, the addition of filler compromises low density, good processibility, flexibility and, in some cases, electrical insulating properties of polymer-based materials. Therefore, it is important to find a way to achieve high thermal conductivity by adding less filler. In this context, this thesis research aims to develop new, conformable thermally conductive polymer composites. Thermoplastic polyurethane (TPU)- hexagonal boron nitride (hBN) composites fabricated by batch foaming were studied as a case example. In particular, foaming has been proposed in this thesis as a potential route to induce filler alignment along the cell wall, and thereby to establish a thermally conductive network in the material system. However, there is a critical level of cell expansion to perfectly align the fillers around the expanded cells. Further expansion would break the thermally conductive network and decrease TPU foam's thermal conductivity (k_eff). Therefore, an understanding of foam morphology is critical to the rational design of improved thermally conductive TPU foams. First of all, a comprehensive experimental study was conducted to identify the foaming behaviors of TPU foams in order to identify appropriate processing windows that would offer flexibility to develop multifunctional TPU composite and nanocomposite foams. TPU foams were fabricated by batch foaming and characterized. The effect of the foaming process (i.e. saturation temperature and saturation pressure) on pore structure (i.e. cell size and cell population density) was investigated. The results of this research demonstrated that by CO₂ foaming it was possible to produce TPU foams at relatively low temperatures (60°C). The results indicated that the cell size and cell density range are significantly wider at lower saturation pressures to varying foaming temperatures. While TPU foams usually yield extremely high cell population density and small cell size, by applying the appropriate foaming conditions, we prepared foams with a wide range of cell sizes, from 21 to 170 µm, and cell population density from 105 to 108 pore/cm³. Secondly, these conditions have been used to investigate the foaming-assisted filler alignment in TPU composite and nanocomposite foams for tailoring the thermal conductivity. Foamed samples at lower saturation temperatures (i.e. 20 and 40°C) yielded higher thermal conductivity than solid counterparts.