Cyclic olefin copolymer foam: A promising thermal insulation material.

• Superior thermal insulating cyclic olefin copolymer (COC) foams are generated. • Attenuation of thermal radiation with COC norbornene (NB) groups has been reported. • The effect of the COC NB content on cellular structures is investigated. • Supercritical fluid aided COC foams with tunable cellular structures are created. In the effort to alleviate climate change and energy consumption issues, thermally insulating polymeric foams can improve energy-management efficiency. To limit the transmission of infrared (IR) radiation through such foams, strong IR-shielding carbon particles are often incorporated to improve thermal insulation performance by blocking IR radiation. However, carbon particles can also dramatically increase solid phase conduction, which counteract efforts to further decrease thermal conductivity. Herein, we report a superior thermal insulation (~28.5 mW·m−1K−1) microcellular foam from ethylene-norbornene (NB) based cyclic olefin copolymers (COCs). Unlike the traditional carbon-filled approach, the incorporation of more NB segments (content from 33, 36, 51 and 58 mol %) in the COC structure greatly improved its ability to block thermal radiation without increasing its solid thermal conductivity. Using the supercritical CO 2 and n-butane as physical blowing agents, we fabricated COC foams with tunable morphology. The void fraction of the foams ranged from 50 to 92%, and they demonstrated a high degree of closed cell content (>98%). In COC foams with given cellular structures (e.g. void fraction of 90%, cell size of 100–200 μm and cell density of ~107 cells/cc), their total thermal conductivity decreases from 49.6 to 37.9 mW·m−1K−1 with increasing NB content from 33 to 58%, which is attributed to high-NB COC's strong ability to attenuate thermal radiation. Subsequently, a highly expanded COC microcellular foam with superior thermal conductivity was successfully developed by tuning both NB content and cellular structure. As a proof of concept, the incorporation of NB segments in COC foams can offer an effective way to shield thermal radiation, opening a new perspective in the development of thermal insulation foams. [ABSTRACT FROM AUTHOR]