Solubility, Diffusivity, and Retrograde Vitrification in PMMA—CO ₂ , and Development of Sub-micron Cellular Structures

A magnetic suspension balance was used to measure solubility of CO ₂ in PMMA in the temperature range 0 to 167 ^° C and at pressures to 61.2 atm. CO ₂ dissolves to considerable extent in PMMA, reaching a value of about 30 wt% at 0 ^° C and 34 atm. Diffusion coefficients, derived from the sorption kinetics, were analyzed to extract glass transition temperature of the PMMA-CO ₂ system over the pressure range of 0 to about 60 atm. The results confirm the existence of retrograde vitrification in this system previously observed by creep compliance and high-pressure thermal analysis techniques. A fundamental understanding of the polymer-gas interactions has led to the development of novel, sub-micron cellular structures.