For the first time, It was demonstrated that a low-density nanoporous medium with a cell density in the order of 0.96*10¹⁶ and the average cell size of ~70nm, out of isotactic polypropylene could be successfully prepared. This was accomplished by the introduction of a complex nano-fibrillar network into the matrix to alter the crystallization kinetics and to manipulate the nanostructure of polypropylene. Importantly, this recyclable medium had a remarkably 8-fold lower thermal conductivity compared to its solid counterpart owing to the diminution of the heat conduction through the solid fraction as well as the trapped air inside the nanopores with the Knudsen effect.

In the same context, polycarbonate is a special polymer that is not only strong but also it shows very unique characteristics that make it a promising candidate for the nanocellular foam fabrication. Among amorphous polymer, PC is the one that can be crystallized with the assistance of CO₂, and the nanocrystals can be harvested as the cell nucleating agent to increase the cell density. Moreover, in this study, it is shown that the solubility of CO₂ in PC increases dramatically at a very low temperature (e.g., up to -40°C), where PC undergoes a transition from a solid to a rubbery state due to swelling and plasticization, so-called the retrograde vitrification behavior.

In this study, a theoretical model based on Henry’s law, Arrhenius equation, and Doolittle equation was developed to predict how the glass transition temperature depresses in the PC/CO₂ system at a different pressure. The experimentally measured solubility data were used to determine the coefficient of the model and to quantify the retrograde vitrification behavior of the PC/CO₂ system. To validate this model, the lower glass transition temperatures of PC/CO₂ , at a few different pressures, were measured by using a high-pressure DSC. The results were in agreement with the theoretically predicted data. Furthermore, I demonstrated the rubbery state below the lower glass transitions by inducing foaming and crystallization in the theoretically predicted rubbery region.