Features of the supercritical CO2-assisted immobilization of fluorinated tetraphenylporphyrins into tetrafluoroethylene copolymers

Abstract

The immobilization of fluorinated tetraphenylporphyrins (FTPPs) into tetrafluoroethylene copolymers (fluoroplast F-42 and MF-4SK, a perfluorinated sulfonic acid cation exchanger in H⁺-form) is conducted in supercritical CO₂ (scCO₂). The effects the conditions of immobilization (the temperature and pressure of scCO₂, reaction time, and the addition of cosolvents) and the structure of the carrier polymer have on the content of porphyrin in these polymers is studied. The porphyrin-loaded polymer systems are shown to exhibit photosensitizing activity in anthracene and cholesterol oxidation in scCO₂. Under conditions of photocatalysis, chemical and functional stability is a feature of only MF-4SK polymer systems; this is attributed to the formation of protonated forms of the porphyrins and their interaction with SO₃⁻-groups of the polymer (an ion exchange process), which prevents leaching of the FTPP from the polymer matrix. The photocatalytic process actually occurs inside the matrix of the perfluorinated copolymer, with the protonated form of the porphyrin acting as a photosensitizer. The rate constant of anthracene photooxidation in the presence of FTPP-loaded MF-4SK films in scCO₂ is found to pass through a maximum as a function of the porphyrin content and the polymer film thickness. The use of such catalytic systems for cholesterol photooxidation in scCO₂ is shown to produce a virtual monoproduct (yield, ~10%): 6-formyl-B-norcholestane-3,5-diol, a compound with high biological activity.