Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer (COC)—including CO 2 solubility, diffusivity, cell nucleation, and foam morphology—were investigated in this article. COCs of low T g (78°C) and high T g (158°C) were studied. Solubilities are 20–50% higher in high T g COC than in the low T g COC across the saturation temperature range. Diffusivities are about 15% higher on average in high T g COC for temperatures up to 50°C. A much faster increase of diffusivity beyond 50°C is observed in low T g COC due to it being in the rubbery state. Under similar gas concentration, high T g COC starts foaming at a higher temperature. And the foam density decreases faster in low T g COC with foaming temperature. Also, high T g COC foams show about two orders of magnitude higher cell nucleation density than the low T g COC foams. The effect of saturation temperature on microcellular foaming can be viewed as the effect of CO 2 concentration. Nucleation density increases and cell size decreases exponentially with increasing CO 2 concentration. Uniform ultramicrocellular structure with an average cell size of 380 nm was created in high‐ T g COC. A novel hierarchical structure composed of microcells (2.5 μm) and nanocells (cell size 80 nm) on the cell wall was discovered in the very low‐density high‐ T g COC foams. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132 , 42226.