Journal Article

Solute Diffusion into Polymer Swollen by Supercritical CO2 by High-Pressure Electron Paramagnetic Resonance Spectroscopy and Chromatography

Melnikov, Mikhail Ya, Parenago, Olga O., Kostenko, Mikhail O., Gromov, Oleg I., Golubeva, Elena N., Minaev, Nikita V., Petrunin, Alexander V., Popova, Anastasia A.

2021

Overview

High-pressure electron paramagnetic resonance (EPR) was used to measure translational diffusion coefficients (Dtr) of a TEMPONE spin probe in poly(D,L-lactide) (PDLLA) and swollen in supercritical CO2. Dtr was measured on two scales: macroscopic scale (>1 μm), by measuring spin probe uptake by the sample; and microscopic scale (<10 nm), by using concentration-dependent spectrum broadening. Both methods yield similar translational diffusion coefficients (in the range 5–10 × 10−12 m2/s at 40–60 °C and 8–10 MPa). Swollen PDLLA was found to be homogeneous on the nanometer scale, although the TEMPONE spin probe in the polymer exhibited higher rotational mobility (τcorr = 6 × 10−11 s) than expected, based on its Dtr. To measure distribution coefficients of the solute between the swollen polymer and the supercritical medium, supercritical chromatography with sampling directly from the high-pressure vessel was used. A distinct difference between powder and bulk polymer samples was only observed at the start of the impregnation process.

• Publisher: MDPI AG,MDPI
• Subject: Carbon dioxide / Chromatography / Coefficients / Diffusion / Electron paramagnetic resonance / Equilibrium / Experiments / Kinetics / NMR / Nuclear magnetic resonance / Polymer blends / Polymers / Porous materials / Pressure vessels / Solvents