160  159  US 9,703,193 B2  Herein Re $^{1 }$is each independently hydrogen, fluorine, methyl  or trifluoromethyl. Re 2  is each independently hydrogen or a  straight, branched or cyclic C$_{1 }$-C$_{20 }$ alkyl or fluoroalkyl  group, or two  Re $^{2 }$in a common monomer may bond together  to form a ring with the carbon atom to which they are  attached, and in this event, they together represent a straight,  branched or cyclic C$_{2}$ -C$_{20 }$alkylene or fluoroalkylene group.  Re 3  is fluorine or hydrogen, or Re 3  may bond with Re 4  to  form a non-aromatic ring of 3 to 10 carbon atoms in total  with the carbon atom to which they are attached.  Re 4  is a  straight, branched or cyclic C$_{1 }$-C$_{6 }$ alkylene group in which  at least one hydrogen atom may be substituted by a fluorine  atom. Res is a straight or branched C$_{1 }$-Ci, alkyl group in  which at least one hydrogen atom is substituted by a fluorine  atom. Alternatively, Re 4  and Res may bond together to form  a non-aromatic ring with the carbon atoms to which they are  attached. In this event, Re 4 ,  Res and the carbon atoms to  which they are attached together represent a trivalent  organic group of3 to 12 carbon atoms in total. Re $^{6 }$is a single  bond or a C$_{1 }$-C$_{4 }$ alkylene. Re$^{7 }$is each independently a single  bond, ---0-, or ----CRe$^{1}$Re 1 -. Re 8  is a straight C$_{1}$-C$_{4 }$ or  branched C$_{1 }$-C$_{4 }$ alkylene group, or may bond with Rs 2  within a common unit to form a C$_{3}$-C$_{6 }$ non-aromatic ring  with the carbon atom to which they are attached. Re 9  is a  C$_{1 }$-C$_{30 }$ divalent hydrocarbon group which may contain a  heteroatom. Re$^{10 }$is a linear perfluoroalkyl group of 3 to 6  carbon atoms, typically 3H-perfluoropropyl, 4H-perfluo› robutyl, 5H-perfluoropentyl or 6H-perfluorohexyl.  Le is each  independently ----C(=O)---0-, ---0-, or ----C(=O)› Re11----C(=O)---0-. Re 11  is a straight, branched or cyclic  C$_{1 }$-C$_{10 }$ alkylene group. The subscripts are in the range:  0s(a’-l)sl, 0s(a’-2)sl, 0s(a’-3)sl, 0sb’sl, 0sc’sl, and  0<( a’-1 )+( a’-2)+(  a’-3 )+b’+c’s  1.  Examples of these units are shown below. Herein Ra $^{1 }$is as  defined above.  OH 