Process development for the synthesis and stabilization of hexafluoropropylene HFP based perfluoropolyethers PFPES

Abstract

Hexafluoropropylene (HFP) based perfluoropolyethers (PFPEs) are a special class of liquid fluoropolymers. Based on average molecular weight, two types of PFPEs are available in the market; low molecular weight (340 u to 760 u) and medium molecular weight (800 u to 4100 u). Medium molecular weight PFPEs find application as a lubricant and low molecular weight PFPEs find application as a solvent and heat transfer fluid in different industries where conventional lubricants, solvents, and heat transfer fluids cannot be used. Industrially, medium molecular weight PFPEs are synthesized by photooxidation of hexafluoropropylene. Perfluoropolyethers synthesized by photo-oxidation of HFP contain acyl fluoride and carboxylic acid as end groups which are highly reactive and stabilization is needed to make them inert. Till now, only fluorination has been established as an effective technique to stabilize PFPEs having reactive end groups but fluorination is a very hazardous technique in terms of handling therefore in present research work feasibility of UV irradiation to stabilize PFPEs was studied in detail. Industrially, low molecular weight PFPEs are produced by cracking of medium/high molecular weight PFPEs in the presence of Lewis acids. Producing low molecular weight PFPEs involves two processes, synthesis of medium molecular weight PFPEs by photo-oxidation method and the cracking of medium molecular weight PFPEs which make production very costly. To bring down the cost of production of low molecular weight PFPEs is a very tough challenge but if they can be synthesized by a one-step process (photo-oxidation method) only and cracking step can be eliminated then cost of producing low molecular weight PFPEs can be reduced drastically. Within the aim of the present study, a single step process was developed which can make the production of low molecular weight PFPEs relatively economical and commercially viable. Photo-oxidation method is already reported in the literature but detailed study of effects of reaction parameters