| abstract |
Use in optical systems as liquids to transmit light at wavenlengths lower than 250 nm, in particular at 157 nm, of perfluoropolyethersnhaving the following formula:n X 1 -O(CF 2 O) n (CF 2 CF 2 O) m (CF 2 CF 2 CF 2 O) p (CF 2 CF 2 CF 2 CF 2 O) q -X 2 nwherein:n the repeating units -CF 2 O-, -CF 2 CF 2 O-, -CF 2 CF 2 CF 2 O-,n-CF 2 CF 2 CF 2 CF 2 O- are statistically distributed along thenchain; -X 1 and -X 2 are perfluoroalkyl chain end groups equal tonor different from each other, having formula -(CF 2 ) z CF 3 n wherein z is 0 or an integer from 1 to 3;n n, m, p, q are 0 or integers comprised between 1 and 100,nwith the proviso that: at least one among n, m, p and q is different from zero; the ratio between the oxygen atoms and the carbon atomsn(O/C) is higher than 0.33; nwherein the chlorine atoms, determined by 19 F-NMR are substantiallynabsent. |