PHOTOOXIDATION OF FUNCTIONALIZED PERFLUORINATED POLYETHERS - II

Three functionalized perfluorinated polyethers (PFPE) were exposed to UV light (lambda > 300 nm) in air, and chemical changes recorded by FT IR and H-1, C-13, F-19 NMR spectrometry. One of the derivatives (ZTET) , end-capped by an hydrogenated ether segment and containing four hydr oxyl groups per molecule, was found to readily undergo photooxidation as shown by rapid development of carbonyl oxidation species and a corr esponding decrease in C-H character. The carbonyl products were assign ed to formate and ester groups respectively, which formation can be de scribed by hydroperoxidation of the functionalized chain ends followed by their photolysis. The formate group is produced as a result of bet a-scission of the secondary hydroperoxide gamma to the perfluorinated chain and is further transformed to a hydroxymethyl chain end group (Z DOL) stabilised by the shielding effect of the adjacent perfluoromethy lene group. The ester formation can be accounted for by oxidation of t he methylene group cr to the perfluorinated chain giving cr carboxylic group which then reacts with ZDOL. The final oxidation product of ZTE T is thus a polymer made of fluorinated polyether segments linked by a n ester bond. The modification of ZTET by urethane or ester end-caps, in order to simulate crosslinks that are present in an eventual isocya nate-cured polyurethane or polyester coating, strongly increased the p hotostability of the compound. This marked increase in stability was a ttributed to both chemical and physical modification of the structure. (C) 1998 Elsevier Science Limited. All rights reserved.