Radical homopolymerization of tetrafluoroethylene initiated by perfluorodiacyl peroxide in supercritical carbon dioxide: Reaction mechanism and initiation kinetics

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• 作者：Anhou Xu ; Hong Li ; Wang Zhang Yuan ; Bing Geng ; Shuxiang Zhang ; Heng Zhang ; Li Wang ; Yongming Zhang
• 关键词：Perfluorodiacyl peroxide ; Polytetrafluoroethylene (Ptfe) ; Supercritical carbon dioxide ; Reaction mechanism
• 刊名：European Polymer Journal
• 出版年：2012
• 出版时间：August, 2012
• 年：2012
• 卷：48
• 期：8
• 页码：1431-1438
• 全文大小：623 K

文摘

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 ¡ãC. Initiation rate constants (k_d) were slightly increased with elevated pressure. The initiation activation energy derived from k_d 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.}