| abstract |
Use in optical systems as liquids to transmit light at wave lengths lower than 250 nm, in particular at 157 nm, of perfluoropolyethers having the following formula:n nX 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 (I)n nwherein:n the repeating units —CF 2 O—, —CF 2 CF 2 O—, —CF 2 CF 2 CF 2 O—, —CF 2 CF 2 CF 2 CF 2 O— are statistically distributed along the chain; —X 1 and —X 2 are perfluoroalkyl chain end groups equal to or different from each other, having formula —(CF 2 ) z CF 3 wherein z is 0 or an integer from 1 to 3; n, m, p, q are 0 or integers comprised between 1 and 100, with 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 atoms (O/C) is higher than 0.33;n nwherein the chlorine atoms, determined by 19 F-NMR are substantially absent. |