A compound of formula (I): ##STR00001## wherein k is 1 or 2; Y is --CH.sub.2CH(CF.sub.3).sub.2 or --(CH.sub.2).sub.nC.sub.F; X is hydrogen, --(CH.sub.2).sub.nR.sub.f, or --C(O)[CF(A)].sub.p-B--R.sub.f, wherein B is a covalent bond, --O-- or --(CH.sub.2).sub.m--; A is --F or --CF.sub.3; and each R.sub.f is independently C.sub.1 to C.sub.6 perfluorinated alkyl, optionally interrupted by one or more oxygens; R.sub.o is R.sub.o.sup.1 or is an alkyl having from about 10 to about 100 carbon atoms, interrupted or substituted by one or more hydrophilic groups; R is hydrogen or a C.sub.1 to C.sub.4 alkyl; and R.sub.o.sup.1 is an aliphatic group of from about 10 to about 100 carbon atoms, interrupted by about from about 5 to about 50 ether oxygens; provided that 1) when Y is --(CH.sub.2).sub.nR.sub.f, R.sub.o is R.sub.o.sup.1; 2) when X is hydrogen, Y is --CH.sub.2CH(CF.sub.3).sub.2; and 3) when X is --(CH.sub.2).sub.nR.sub.f and Y is --(CH.sub.2).sub.nR.sub.f, R.sub.o is R.sub.o.sup.1.