Abstract
The α,ω-dialkoxyfluoropolyethers (DA-FPEs) characterized by the structure RHO(CF2CF2O)n(CF2O)mRH have been developed as a new class of environmentally friendly hydrofluoroethers (HFEs) suitable as solvents, long-term refrigerants, cleaning fluids, and heat transfer fluids. Synthetic methodologies for DA-FPEs described here consist of radical-initiated oxypolymerization of olefin, peroxy-elimination reaction in peroxidic perfluoropolyethers (P-PFPEs) and further chemical modification of α,ω-diacylfluoride PFPE. The physical properties of selected α,ω-dimethoxyfluoropolyethers (DM-FPEs) have been evaluated and compared with analogous hydrofluoropolyethers (HFPEs) having -OCF2H as end-groups. Atmospheric implications and global warming potentials (GWPs) of selected DA-FPEs are also considered.
Highlights
RHO(CF2CF2O)n(CF2O)mRH have been developed as a new class of environmentally friendly hydrofluoroethers (HFEs) suitable as solvents, long-term refrigerants, cleaning fluids, and heat transfer fluids
Due to the presence of the above-mentioned alkoxy-groups as ending groups, they show good solvent properties with several organic liquids, such as ketones and alcohols [5]. All these appealing properties of DA-FPEs make them excellent candidates as CFC, perfluocarbons and halons substitutes in a number of applications, like foaming and fire extinguishing agents, cleaning agents for sophisticated electronic devices and heat transfer fluids [6,7,8]
Hydrofluoropolyethers DA-FPEs are prepared through the reaction of diacyl fluoride PFPEs (DAF-PFPEs) with electrophiles in the presence of a source of fluorine ions, generally, metal fluorides. This process comprises two steps (Figure 4): Firstly, in aprotic polar solvent, DAF-PFPEs react with fluoride ions released from metal fluorides to form metal perfluoroalkoxides
Summary
Oxidative polymerization of perfluoroolefinc monomers like tetrafluoroethylene (TFE) by molecular oxygen into P-PFPEs (A) described in Figure 1, is a well-known reaction [9]. The forming peroxidic polymer has the following general structure: TO-(CF2CF2O)p-(CF2O)r-(O)q-T’, comprising fluoroether repeating units (-CF2CF2O- and -CF2O-), interspersed peroxy units (-CF2CF2OO- and -CF2OO-) and perfluorinated alkyl groups, acyl fluoride or fluoroformate as chain end-groups (T, T’). This oxypolymerization can be activated either by high energy UV light or by employing elemental fluorine or perfluoroalkyl hypofluorites, especially CF3OF, as chemical initiators [9]. The chemical reduction is performed with reducing agents, such as hydrogen iodide or with molecular hydrogen in the presence of a noble metal catalyst (e.g., Palladium) [14]
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