As part of a continuing effort to effect the chemical modification of fluorocarbon polymers, we have been engaged in the examination of substitution reactions of poly(chlorotrifluoroethylene) (PCTFE). Previous efforts by ourselves and others have shown that two electron reduction processes generally proceed through elimination and on to other side reactions, while one electron processes can sometimes be trapped to afford a clean substitution of trapping agent for chloride, often to rather large degrees of functionalization.
We were intrigued by the prospect of using oxidative addition processes to effect substitution reactions on PCTFE. Examination of the literature indicated that perfluorocarbon ligands bound to transition metals were not particularly prone to elimination, but that oxidative addition to a carbon-chlorine bond (rather than the weaker bonds from carbon to iodine or bromine) was not well known. As a result, we undertook a study of the reactions of metal carbonyl complexes with PCTFE, in the forms of KelF 6061 (3M) and Neoflon M400H (Daikin).
Reaction of PCTFE with anionic metal carbonyls (Na2Fe(CO)4, etc.) leads to extensive elimination along the polymer backbone, as indicated by IR analysis as well as discoloration of the bulk material. Reaction with Group 6 metal carbonyl species (chromium hexacarbonyl, as well as the molybdenum and tungsten analogues) in DMF at 90C leads to formation of the acyl metal species, with subsequent addition of an external nucleophile and isolation of the acid derivative. PCTFE derivatized by carboxylic acid and amide functional groups are isolated with minimal side reaction.
All of the above species are characterized by FT-IR and elemental analysis. The carboxylate is additionally characterized by titrimetric analysis and scanning electron microscopy. A depth profile is reported by means of ATR-FT-IR and examination of attempts to trap the perfluoroalkyl metal species before carbonyl migration are outlined.
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