an integer of 1 to about 10 (preferably 1 to about 3), q is an integer of 1 to about 20, and X is selected from the group consisting of hydrogen and fluorine; Rf b is a linear or branched, perfluorinated or partially-fluorinated alkylene group having from 1 to about 10 carbon atoms (preferably, from about 2 to about 6 carbon atoms) and optionally containing one or more catenary ether oxygen atoms;