| Abstract | The sorption and diffusion of CO₂ in linear and branched polycarbonates were investigated using a high-temperature, high-pressure gravimetric technique. The branched structure does not affect gas solubility, but affects the gas diffusivity in the sub-Tg region, with CO₂ diffusing faster through the branched structure than the linear one. Both solubility and diffusivity depend linearly on pressure at temperatures above Tg, but demonstrate complicated pressure dependence at temperatures below Tg. In the sub-Tg region, volume change of the polymer matrix accompanying the gas dissolution was measured using a dilatometer. The plasticized Tgs obtained from dilation and solubility measurements agreed with those obtained directly by high-pressure DSC. In addition, a plasticization related densification phenomenon was observed in the sub-Tg region. The competing effects of dilation and densification suggest significant implications in terms of solid state processing of microcellular foams. |
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