Molecular redesign of expanded polystyrene to allow use of carbon dioxide as a foaming agent. I. Reversible binding of CO₂

Environmental concerns, associated with the production of expanded plastics using hydrocarbon blowing agents, have spurred interest in environmentally‐friendly technology by which cellular materials, particularly expanded polystyrene, can be produced. Consequently, we have explored the possibility of using styrene‐based, amino‐functional copolymers to generate expandable systems, which would rely solely on CO 2 as a blowing agent. Carbon dioxide is an attractive foaming agent in that it can be readily extracted from the air, is nonflammable, and exhibits low toxicity. Using a styrenic copolymer, functionalized with ethylenediamine (EDA), the results of this study show that aminated polymers are capable of reversibly binding weakly acidic gases, CO 2 in particular. While the reaction products (polymer‐bound zwitterions) are stable under ambient conditions, decarboxylation can be thermally induced cleanly and easily. Work underway in our laboratory shows that microporous, as well as nonporous EDA‐functional copolymers, are effective, thermally‐reversible sorbents for acid gases. Furthermore, preliminary results show that these materials may also find potential applications in facilitated transport membrane technology.