Polymer-CO2 systems exhibiting retrograde behavior and formation of nanofoams

Abstract

The sorption of compressed gases in polymers causing a reduction in the glass transition temperature (Tg) 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 (Cp) 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 Cp 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. © 2006 Society of Chemical Industry.