A dielectric relaxation study of plasticization of poly(ethyl methacrylate) by carbon dioxide

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Abstract
Plasticization of poly(ethyl methacrylate) (PEMA) by CO2 is investigated by dielectric relaxation spectroscopy. The dissipation factor of a dielectric cell containing the film and air gaps is measured as a function of frequency (1–10,000 kHz) and CO2 pressure (0–60 atm) over the temperature range 35–115°C. A maximum in the frequency dependence of the dissipation factor, which is attributed to the α relaxation of PEMA, shifts to higher frequency with increasing temperature, pressure, or concentration. The apparent activation energy of the isosteric relaxation decreases from 28 to 23 kcal/mol as the concentration is increased from 0 to 90 cm3 (STP)/cm3 (polym). The relaxation peak temperature at fixed frequency decreases with increasing concentration. The effect of hydrostatic pressure on the dielectric relaxation is estimated and compared with values for the PEMA‐He and PEMA‐Ar systems. The plasticizing effect of sorbed CO2 is discussed on the basis of the relaxation data.

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