Medium to low density thermoplastic nanofoams have previously been produced using nanoparticles as nucleating center. Here we show that by designing the molecular structure of the polymer matrix to achieve high CO2 solubility while controlling the glass transition temperature, it is possible to produce nanofoams with cell nucleation densities as high as 1016/cm3 without introducing nucleation aids. This was achieved by maximizing foam expansion without uncontrolled cell ripening for a series of acrylic copolymers, which were foamed under a set of standard conditions. To predict the role of foaming conditions on foam characteristics, a theoretical foaming model was built to simulate cell nucleation, growth and foam stabilization. Experimental or predicted properties of the polymer/carbon dioxide mixture were used as inputs. Despite simplifying assumptions, such as the use of classical nucleation equations, the semi-quantitative model provides insight into the foam expansion behavior and validates experimental observations.
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