The thermal stability of poly(methyl methacrylate) doped with 0.16 wt% copper naphthenate was examined by monitoring weight loss over time at 220°C. The addition of copper naphthenate decreased the thermal stability by about 2 orders of magnitude. Significant enhancement of the thermal stability was accomplished by extracting the copper ions from the polymer matrix. The extraction was performed in liquid carbon dioxide at room temperature and 2 500 psi with thenoyltrifluoroacetone employed as a carbon dioxide-soluble chelating agent. After the extraction process was completed, the thermal stability of the polymer/metal system was within about 0.6 orders of magnitude of the value for the neat polymer.