Direct measurement of the carbon dioxide-induced glass transition depression in a family of substituted polycarbonates

Abstract

We present a method for the direct measurement of the glass transition temperature of compressed gas–polymer systems. The technique utilizes a Setaram C80D microcalorimeter equipped with high-pressure cells. Pressurizing the cells and running in scanning mode allows direct determination of the glass transition temperature. To validate the method, Tg measurements of the CO2–poly(methyl methacrylate) system as a function of gas phase pressure were made. The results compare favorably with literature values. However, the effects of foaming appear to interfere with Tg measurement at the highest gas pressures. The CO2-induced Tg depression of a series of polycarbonates was also measured. The magnitude of the Tg depression increases with decreasing glass transition temperature, reflecting an increase in intrinsic chain mobility, as evidenced by the glass transition temperature. The data correlate well with the Chow model. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1441–1449, 1998