Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1398307 | European Polymer Journal | 2012 | 8 Pages |
Radical homopolymerizations of tetrafluoroethylene (TFE) in supercritical carbon dioxide (sc-CO2) initiated by bis(perfluoro-2-n-propoxypropionyl) peroxide (BPPP) were conducted. Low molecular weight polytetrafluoroethylenes (PTFEs) which are widely used in diverse fields with stable end groups were successfully obtained. PTFEs were characterized by solid-state 19F NMR and FT-IR spectroscopy. From rational assignment of the characteristic signals, an overall reaction mechanism explaining the homopolymerization processes is proposed. The carboxyl radicals resulted from thermal decomposition of BPPP were completely decarboxylated to n-C3F7OCF(CF3) before reacting with TFE. Additionally, a small amount of n-C3F7OCF(CF3) rearranged into n-C3F7 with decreased rearrangement fraction from 0.11 to 0.04 when the reaction temperature was lowered from 35 to 5 °C. Initiation rate constants (kd) were slightly increased with elevated pressure. The initiation activation energy derived from kd is 90.3 kJ mol−1, which is much lower than those of the other systems where nonfluorinated diacyl peroxides are used. Such mechanism and kinetics insights into the homopolymerizations of TFE in sc-CO2 will be instructive for the syntheses of fluoropolymers with desired properties in future.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The overall mechanism for TFE homopolymerization initiated by BPPP was presented. ► The carboxyl radical completely decarboxylated before reacting with TFE. ► A small fraction of n-C3F7OCF(CF3) radicals rearranged into n-C3F7 radicals. ► The initiation activation energy for BPPP is very low.