One step synthesis of low molecular weight perfluoropolyethers (PFPEs) by photo-oxidation of hexafluoropropylene (HFP)

A new single step process was developed to synthesize low molecular weight perfluoropolyethers (PFPEs) (1.5 cSt (cSt) to 4 cSt (cSt)) which can replace the conventional two steps industrial process. A new method (method 1) was discovered accidently during synthesizing medium molecular weight perfluoropolyethers by already established photo-polymerization method (method 2). To understand the mechanism, PFPEs obtained from method 1 and method 2 were analyzed by 19F-NMR spectroscopy, FTIR spectroscopy, TGA analyzer and gravimetrically. Properties of PFPEs obtained from both the methods were compared. Low viscosity PFPEs (1.5 cSt to 4 cSt) were obtained when method 1 was applied while medium viscosity (18 cSt-20 cSt) product was obtained from method 2. The average molecular weight of PFPEs obtained from method1 (686 Da) was found half of the PFPEs obtained from method 2 (1200 Da (Da)). Acid value (340 mg/gm) of PFPEs obtained from method 1 was almost three times higher than the acid value (100 mg/gm) of PFPEs obtained from method 2. Very low viscosity and a high acid value of the synthesized perfluoropolyethers obtained from method 1 in comparison to method 2 confirmed the presence of the high proportion of low molecular weight PFPEs in the product. After establishing the mechanism of method 1, the effect of process parameters such as reaction time, reaction temperature and reaction pressure on yield and viscosity was also studied in detail.