Polymer–CO2 systems exhibiting retrograde behavior and formation of nanofoams

The sorption of compressed gases in polymers causing a reduction in the glass transition temperature (T_g) is well established. There is, however, limited information on polymer–gas systems with favorable interactions, producing a unique retrograde behavior. This paper reports on using a combination of established techniques of in situ gravimetric and stepwise heat capacity (C_p) measurements using high‐pressure differential scanning calorimetry (DSC) to demonstrate the occurrence of this behavior in acrylonitrile–butadiene–styrene copolymer (ABS)–CO₂ and syndiotactic poly(methyl methacrylate) (sPMMA)–CO₂ systems. The solubility and diffusion coefficient of CO₂ in the range 0 to 65 °C and pressures up to 5.5 MPa were determined, which resulted in a heat of sorption of ? 15.5 and ? 15 kJ mol^?1, and an activation energy for diffusion of 28.3 and 32.1 kJ mol^?1 in the two systems, respectively. The fundamental kinetic data and the changes in C_p of the polymer–gas systems were used to determine the plasticization glass transition temperature profile, its relationship to the amount of gas dissolved in the polymer, and hence the formation of nano‐morphologies. Copyright © 2006 Society of Chemical Industry