Electron paramagnetic resonance spin probe study of carbon dioxide-induced polymer plasticization

Abstract

Steady-state electron paramagnetic resonance (EPR) spectroscopy using nitroxide spin probes has been used to investigate the plasticization of poly(vinyl acetate) and poly(ethyl methacrylate) by carbon dioxide. By varying the CO 2 pressure at constant ambient temperature, the glass transition for each polymer could be depressed to 25°C. This effect has been quantified by a parameter P 50G, obtained by plotting the EPR spectral width as a function of CO 2 pressure. Certain spin probes showed free volume distribution effects, manifested in the EPR spectra as "double peaks." Possible reasons for this phenomenon are presented and discussed, and the efficacy of CO 2 as a plasticizer is clearly demonstrated by direct comparison with di-n-butyl phthalate. © 2005 Wiley Periodicals, Inc.