Diffusion of the Tempone Spin Probe in Poly(Methyl Methacrylate) and Poly(D,L-Lactide) Plasticized with Sub- and Supercritical CO2

The rotational and translational mobility coefficients of the TEMPONE spin probe in polylactide (PLA) and poly(methyl methacrylate) (PMMA) plasticized with supercritical (SC) and subcritical (SUB) CO2 were studied by EPR spectroscopy. The translational diffusion coefficients of TEMPONE in the PMMA–SC-CO2 system are three orders of magnitude lower than those in PLA–SC-CO2 and are on the order of 10–14 and 10–11 m2/s, respectively. The activation energy of TEMPONE rotation in PLA–SC-CO2 is 22 ± 5 kJ/mol. When PLA is impregnated with the probe under subcritical conditions, desorption of the radical is predominant throughout the experiment. The spectrum of TEMPONE in PLA–SUB-CO2 is a superposition of a narrow signal similar to the spectrum of TEMPONE in PLA–SC-CO2 and a broad isotropic signal due to the magnetic concentration of TEMPONE probes in the surface layer of the polymer. A decrease in the local concentration with time is accompanied with the appearance of rotational anisotropy in the spectra of particles of the second type. The results obtained indicate the advantages of using SC-CO2 as a solvent for the impregnation of polymers, primarily due to high diffusion coefficients.