Key words: supercritical carbon dioxide, subcritical carbon dioxide, poly-D,L-lactide, polymethylmethacrylate, electron spin resonance spectroscopy, 2,2,6,6-tetramethyl-piperidine-1-oxyl, spin probe, diffusion coefficient, spin-spin exchange interactions, distribution constant, supercritical fluid chromatography
The rotational and translational coefficients of the TEMPONE spin probe mobility were studied by ESR spectroscopy in the PLA and PMMA-based polymers plasticized with supercritical as well as subcritical carbon dioxide. Translational diffusion coefficients of TEMPONE in the PMMA-SC-CO2, system are 3 times inferior in comparison to PLA-SC-CO2 and the corresponding values are of 10-14 and 10-11 m2/s order of magnitude. The rotation activation energy of a value 22±5 kJ/mole was determined for the TEMPONE rotation in PLA-SC-CO2. It was found out that desorption of the radical exceeds TEMPONE diffusion into bulk PLA under subcritical conditions during the experimental period. Spectra of TEMPONE in PLA-SUB-CO2 turned out to be a superposition of two signals: a narrow one, which is similar to that of TEMPONE in PLA-SC-CO2, and a broad isotropic one caused by the TEMPONE paramagnetic particles accumulation in a polymer volume proximate to the surface. As local concentration decreases with time, the rotational anisotropy is exposed in the latter signal. The study gives an outlook on the SC-CO2 use as promising media to the polymer impregnation primarily taking into consideration both it’s and solutes’ higher mass diffusivity.
doi:10.34984/SCFTP.2023.18.1.005