Perfluoropolyether(PFPE) was first studied in 1960s. It is a kind of special perfluoropolymer compound with average molecular weight ranging from 500 to 16000. There are only three elements in the molecule: C, F and O, the existing C-O and C-F bonds are highly stable. It has the features of excellent thermal resistance, oxidation resistance, radiation resistance, corrosion resistance and non-flammability, etc. It has been used as a very reliable lubricant in military, aerospace and nuclear industries for decades. Now perfluoropolyether(PFPE) is widely used in chemical industry, electronics, electrical appliances, machinery, nuclear industry, aerospace field.
According to the different monomers and polymerization methods, PFPE with different molecular structures of K, Y, Z and D types can be obtained.
The K-type structure is CF3CF2CF2O [CF(CF3)CF2O]nCF(CF3)COF. It is a series of branched polymer formed by the polymerization of hexafluoropropylene oxide (HFPO) under the catalysis of CsF.
The Y-type structure is CF3O (C3F6O)m(CF2O)nCF3. It is a polymer formed by photooxidation of hexafluoropropylene (HFP) under ultraviolet light. Its molecular weight is generally between 1000 and 10000.
The Z-type structure is CF3(C2F4O)m(CF2O)nCF3. It is a linear polymer formed by photooxidation of tetrafluoroethylene (TFE) under ultraviolet light. Its molecular weight is generally between 1000 and 100000.
The D-type structure is C3F7O(CF2CF2CF2O)mC2F5. It is a polymer obtained by direct fluorination of the polymer product of tetrafluorooxyheterocyclic butane.
At present, there are two main synthesis methods of perfluoropolyether: photocatalytic polymerization and anionic catalytic polymerization.
1) Photocatalytic Polymerization
It uses tetrafluoroethylene or hexafluoropropylene as raw materials, reacts with oxygen under ultraviolet irradiation at low temperature, and obtains polyethers with slightly different structures through oxidative polymerization. Taking tetrafluoroethylene as an example, besides acyl fluoride terminal group, there are unstable peroxide groups in the main chain of the crude product, which need to be eliminated by heating or illumination, and then stabilized by elemental fluorine. This method was commercialized in the 1960s. Its molecular structure is Y-type and Z-type.
2) Anionic Catalytic Polymerization
It uses Perfluoropropylene oxide(HFPO) as raw material, fluoride ion as catalyst in non-proton solvent, Perfluoropropylene oxide oligomer containing acyl fluoride terminal group can be obtained, and perfluoropolyether can be obtained by stabilization of its active acyl fluoride terminal group. This method was first commercialized in the 1970s. The main commodities are Krypton produced by DuPont Company in the United States and Demnum produced by Dajin Company in Japan (Dajin Company’s perfluoropolyether technology has been licensed by 12 national patents), and the molecular structure is K-type and D-type.