97  US 9,221,742 B2  98  hydrogen atom may be substituted by a fluorine atom. R $^{118 }$is  a straight or branched C $_{1 }$-C $_{10 }$alky 1 group in which at least one  hydrogen atom is substituted by a fluorine atom. Alterna› tively, R$^{117 }$and R$^{118 }$may bond together to form a non-aro› matic ring with the carbon atoms to which they are attached.  5  In this event, R 117 , R $^{112 }$and the carbon atoms to which they  are attached together represent a trivalent organic group of 2  to 12 carbon atoms in total. R $^{119 }$is a single bond or a C$_{1 }$-C$_{4 }$ alkylene. R $^{120 }$is each independently a single bond, ---0-, or  -CR$^{114}$R 114 -.  R$^{121 }$isastraightorbranchedC$_{1}$-C$_{4}$ alkylene  10  group, or may bond with R $^{115 }$within a common monomer to  form a C$_{3}$ -C$_{6 }$ non-aromatic ring with the carbon atom to  which they are attached. R $^{122 }$is 1,2-ethylene, 1,3-propylene,  or 1,4-butylene. Rf is a linear perfluoroalkyl group of 3 to 6  15  carbon atoms, typically 3H-perfluoropropyl, 4H-perfluo› robutyl, 5H-perfluoropentyl, or 6H-perfluorohexyl. X $^{2 }$is  each  independently  ----C(=O)---0-,  ---0-,  or  -C(=O)-R$^{123}$----C(=O)---0-.  R 123  is  a  straight,  branched or cyclic C$_{1 }$-C$_{10 }$alkylene group. The subscripts are 20  in the range:  0s(a’-1)<1, 0s(a’-2)<1, 0s(a’-3)<1,  0<(a’-l)+(a’-2)+(a’-3)<1,  0sb’<l, 0sc’<l, and  0<( a’-1 )+( a’-2)+(  a’-3 )+b’+c’s  1.  Exemplary units are shown below.  /  ’;==o  ~  HO  0  OH  (~)  /  ’j==o  C~CC;  F  OH 