US Patent 7186787 Linear perfluoropolyethers having an improved thermooxidative stability

Linear perfluoropolyethers of formula:T-O(CF2O)n(CF2CF2O)m(CF2CF2CF2O)r(CF2CF2CF2CF2O)s-T1  (I)wherein n, m, r, s are integers such that the polymer number average molecular weight is comprised between 700 and 100,000 and the n/(n+m+r+s) ratio ranges from 0.05 to 0.40, and respective preparation process by addition of a peroxidic perfluoropolyether of formula (III):T4—O(CF2O)n′(CF2CF2O)m′(O)h-T5  (III)having a PO from 1.8 to 4, to a perfluoropolyether oil preheated at a temperature comprised between 150° C. and 250° C. and subsequent exhaustive fluorination of the obtained compound.